Difference between revisions of "Lazarus Database Overview"

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(See also)
(Using the SQLdb components)
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=== Using the SQLdb components ===
+
=== Using the SQLdb components with TSQLIte3Connection ===
  
To use these components we will replace the TQLite3Dataset from the previous example with a combination of three components from the SQLdb tab: TSQLite3Connection, TSQLTransaction and TSQLQuery (the TSQLQuery is the one that is now acting as our TDataset, in the simplest case it just represents one of our tables). For the sake of simplicity I assume you already have an existing sqlite database file and don't need to create a new one one now. You should have a look at this [[SqlDBHowto|SqlDBHowto]] which also has some useful information about the SQLdb components.  
+
To use these components we will replace the TQLite3Dataset from the previous example with a combination of three components from the SQLdb tab: TSQLite3Connection, TSQLTransaction and TSQLQuery (the TSQLQuery is the one that is now acting as our TDataset, in the simplest case it just represents one of our tables). For the sake of simplicity I assume you already have an existing sqlite database file and don't need to create a new one one now. You should also have a look at this [[SqlDBHowto|SqlDBHowto]] which also has some useful information about the SQLdb components.  
  
 
The three components are connected with each other as usual: In the TSQLQuery set the properties Database and Transaction, in the TSQLTransaction set the property Database. There is not much to do in the Transaction and Connection components, most interesting stuff will be done in the TSQLQuery. Configure the components as follows:
 
The three components are connected with each other as usual: In the TSQLQuery set the properties Database and Transaction, in the TSQLTransaction set the property Database. There is not much to do in the Transaction and Connection components, most interesting stuff will be done in the TSQLQuery. Configure the components as follows:
  
 
TSQLite3Connection:
 
TSQLite3Connection:
* DatabaseName: Set this property to the file name (absolute path!) of your sqlite file. Unfortunately you cannot simply use a relative path that works unchanged at designtime and at runtime. You should make sure that at application start the correct path to the file is always set programmatically, no matter what it contained at designtime.
+
* DatabaseName: Set this property to the file name (absolute path!) of your SQLite file. Unfortunately you cannot simply use a relative path that works unchanged at designtime and at runtime. You should make sure that at application start the correct path to the file is always set programmatically, no matter what it contained at designtime.
  
 
TSQLQuery:
 
TSQLQuery:
 
* SQL: Set it to some simple select query on one of your tables. For example if you have a table 'foo' and want this Dataset to represent this table then just use the following: <code>SELECT * FROM foo</code>
 
* SQL: Set it to some simple select query on one of your tables. For example if you have a table 'foo' and want this Dataset to represent this table then just use the following: <code>SELECT * FROM foo</code>
  
* Active: Set this to True from within the IDE to test whether it is all set up correctly. This will also automatically activate the tranaction and the connection objects. If you receive an error then either the DatabaseName of the connection is not correct or the SQL query is wrong (remember: I assumed for simplicity that you already have an existing sqlite database with tables in it). Later if we are done adding the fields (see below) set them all to inactive again, we don't want the IDE to lock the SQLIte database (single user!) when testing the application.
+
* Active: Set this to True from within the IDE to test whether it is all set up correctly. This will also automatically activate the transaction and the connection objects. If you receive an error then either the DatabaseName of the connection is not correct or the SQL query is wrong (remember: I assumed for simplicity that you already have an existing SQLite database with tables in it). Later if we are done adding the fields (see below) set them all to inactive again, we don't want the IDE to lock the SQLite database (single user!) when testing the application.
  
 
* Now we can add Fields to our TSQLQuery. While the components are still set to active do a right click and "edit fields...". Click the "+" button and add fields. It will list all fields your SQL query returned. Add every field you will need, you can also add lookup fields here, in this case just make sure you have already defined all needed fields in the other datasets before you start adding lookup fields that refer to them. If your table has many columns and you don't need them all you can just leave them away, you can also make your SQL a bit more specific.  
 
* Now we can add Fields to our TSQLQuery. While the components are still set to active do a right click and "edit fields...". Click the "+" button and add fields. It will list all fields your SQL query returned. Add every field you will need, you can also add lookup fields here, in this case just make sure you have already defined all needed fields in the other datasets before you start adding lookup fields that refer to them. If your table has many columns and you don't need them all you can just leave them away, you can also make your SQL a bit more specific.  
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* In your code you need to call SQLQuery.ApplyUpdates and SQLTransaction.Commit, TSQLQuery.AfterPost and AfterInsert events are a good place for this when using it with data aware controls but of course you can also postpone these calls to a later time. If you don't call them it will not update the database.
 
* In your code you need to call SQLQuery.ApplyUpdates and SQLTransaction.Commit, TSQLQuery.AfterPost and AfterInsert events are a good place for this when using it with data aware controls but of course you can also postpone these calls to a later time. If you don't call them it will not update the database.
  
* "Database is locked": SQLite is an embedded single user database. Once you are done defining all the fields of your query objects set all objects at design time to inactive again before you run your Application. Use the Form's OnCreate event to set the path and activate the objects at runtime. If you have more than one TSQLQuery and have lookup fields defined then be sure to activate them in the correct order. Most of the things you set in the TSQLQuery from within the IDE don't require them to be active at design time, the only exception is defining the fields where it needs to read the table design, so inactive at design time should be the nomal state.
+
* "Database is locked": SQLite is an embedded single user database. Once you are done defining all the fields of your query objects set all objects at design time to inactive again before you run your Application. Use the Form's OnCreate event to set the path and activate the objects at runtime. If you have more than one TSQLQuery and have lookup fields defined then be sure to activate them in the correct order. Most of the things you set in the TSQLQuery from within the IDE don't require them to be active at design time, the only exception is defining the fields where it needs to read the table design, so inactive at design time should be the normal state.
  
* Yor tables should all have a primary key and you must make sure that the corresponding field has pfInKey and nothing else in its PoviderFlags (these flags control how and where the field is used when automatically constructing the update and delete queries).
+
* Your tables should all have a primary key and you must make sure that the corresponding field has pfInKey and nothing else in its PoviderFlags (these flags control how and where the field is used when automatically constructing the update and delete queries).
  
 
* If you are using lookup fields  
 
* If you are using lookup fields  
** make sure the ProviderFlags for the lookup field is completely empty so it won't attempt to use it's name in an update query. The lookup field itself is not a data field, it only acts on the value of another field, the corresponding key field, and only this key field will later be used in the update queries. You can set the key field to hidden because usually you dont want to see it in your DBGrid but it needs to be defined.
+
** make sure the ProviderFlags for the lookup field is completely empty so it won't attempt to use it's name in an update query. The lookup field itself is not a data field, it only acts on the value of another field, the corresponding key field, and only this key field will later be used in the update queries. You can set the key field to hidden because usually you don't want to see it in your DBGrid but it needs to be defined.
 
** LookupCache must be set to True. At the time of this writing for some reason the lookup field will not display anything otherwise (but still work) and strangely the exact opposite is the case when working with the TSQLite3Dataset or other TXXXDataset components, here it must be set to False. I'm not yet sure whether this is intended behavior or a bug.
 
** LookupCache must be set to True. At the time of this writing for some reason the lookup field will not display anything otherwise (but still work) and strangely the exact opposite is the case when working with the TSQLite3Dataset or other TXXXDataset components, here it must be set to False. I'm not yet sure whether this is intended behavior or a bug.
  
 
* Usually with simple tables you won't need to set any of the InsertSQL, UpdateSQL and DeleteSQL properties, just leave them empty. If you have the ProviderFlags of all your fields set correctly it should be able to create the needed SQL on the fly. An example for an update query would be <code>UPDATE foo SET bar=:bar,baz=:baz WHERE id=:id;</code> The placeholders start with : and refer to the Name properties of the TField objects. You need to set these queries manually when your dataset is composed of more complex SQL from multiple tables where it cannot figure out on its own how to correctly update the underlying data.
 
* Usually with simple tables you won't need to set any of the InsertSQL, UpdateSQL and DeleteSQL properties, just leave them empty. If you have the ProviderFlags of all your fields set correctly it should be able to create the needed SQL on the fly. An example for an update query would be <code>UPDATE foo SET bar=:bar,baz=:baz WHERE id=:id;</code> The placeholders start with : and refer to the Name properties of the TField objects. You need to set these queries manually when your dataset is composed of more complex SQL from multiple tables where it cannot figure out on its own how to correctly update the underlying data.
 +
 +
After the above is all set up correctly you should now be able to use the TSQLQuery like any other TDataset, either by manipulating it's data programmatically or by placing a TDatasouce on the Form, connecting it to the TSQLQuery and then using data contols like TDBGrid etc.
  
 
== Lazarus and MSSQL ==
 
== Lazarus and MSSQL ==

Revision as of 15:00, 5 November 2011

Template:Translate

Overview

This tutorial is about getting Lazarus to work with a variety of existing databases.

Lazarus supports several databases out-of-the-box, however the developer must install the adequate packages for each one. You can access the database through code or by dropping components on a form. The data-aware components represent fields and are connected by setting the DataSource property to point to a TDataSource. The Datasource represents a table and is connected to the database components (examples: TPSQLDatabase, TSQLiteDataSet) by setting the DataSet property. The data-aware components are located on the "Data Controls" tab. The Datasource and the database controls are located on the "Data Access" tab.

Lazarus and MySQL

Get MySQL working in Linux or Windows

Follow the instructions in the MySQL User Manual. Make sure that the mysqld daemon runs reliably, and that all potential users (including root, mysql, yourself and anybody else that may need it) have as many privileges as they need, from as many hosts as may be needed (including 'localhost', the local host's name, any other hosts on your network) as far as is consistent with security. It is preferable that all users including root have passwords. Test the action of the database system using the examples given in the manual, and check that all users really do have reliable access.

Get MySQL working for FPC in text mode

There is a directory with an example program in $(fpcsrcdir)/packages/base/mysql/. You can find the fpc source directory in Lazarus: Environment menu -> Environment Options -> Paths tab -> FPC source directory. Possible paths for the mysql directory are /usr/share/fpcsrc/packages/base/mysql/ (rpm install) or C:\lazarus\fpcsrc\packages\base\mysql\ (windows). This directory also contains the units mysql.pp, mysql_com.pp and mysql_version.pp. Before running the test script, you need to create a database called testdb: do this by logging into the mysql monitor (as root with full privileges) and issuing the following SQL statement <sql>CREATE DATABASE testdb;</sql> then make sure that all relevant users have appropriate access privileges to it <sql>GRANT ALL ON testdb TO johnny-user IDENTIFIED BY 'johnnyspassword';</sql> There is a script called mkdb which you should now try to run:

sh ./mkdb

This will probably fail, as the system will not allow an anonymous user to access the database. So change the script using an editor so that the line invoking mysql reads:

mysql -u root -p  ${1-testdb} << EOF >/dev/null

and try running it again, entering your password when prompted. With luck you might have managed to create the test database: test it (while logged in to the mysql monitor) by issuing the mysql statement <sql>select * from FPdev;</sql> You should see a table listing the ID, username and email address of some of the FPC developers.

Now try to run the test program testdb.pp (this may need to be compiled, and will almost certainly fail on the first attempt!!).

I found that the program could not connect to mysql for several reasons:

  • My system (SuSE Linux v9.0) installs mysql v4.0.15, not the version3 for which the package was designed.
  • The program needs to have user names and passwords to get access to the database.
  • The compiler needs to know where to find the mysql libraries (IF YOU HAVEN'T INSTALLED THE MYSQL DEVELOPMENT LIBRARIES, DO SO NOW!)

I created a copy of testdb.pp called trydb.pp, rather than editing the original - this means that the original files still get fixed in subsequent CVS updates. I also copied the files found in the subdirectory mysql/ver40/ into the main mysql/ subdirectory, renaming them mysql_v4.pp, mysql_com_v4.pp and mysql_version_v4.pp, being sure to rename the units within each file correspondingly. I changed the uses statement in trydb.pp to <delphi>uses mysql_v4</delphi> and the statement in mysql_v4.pp to

<delphi>uses mysql_com_v4</delphi>

I added a line to /etc/fpc.cfg to point to my libraries:

-Fl/lib;/usr/lib

The following step might not be necessary if the devel-libraries are installed as the links will be created for you, but it never hurts to check. I had to find the real name of the mysqlclint library in the /usr/lib directory and in my case I had to issue the shell command:

ln -s libmysqlclient.so.12.0.0 lmysqlclient

to make a symbolic link allowing FPC to find the library. For good measure I also created the link

ln -s libmysqlclient.so.12.0.0 mysqlclient

and placed similar links in various other directories: not strictly necessary, but just in case ...! Some users might need to add the following link:

ln -s libmysqlclient.so.12.0.0 libmysqlclient.so

I modified trydb.pp to include user details, initially by adding host, user and password as constants:

<delphi>const

 host : Pchar= 'localhost';
 user : Pchar= 'myusername';
 passwd: Pchar = 'mypassword';</delphi>

I also found that I couldn't connect to mysql using the mysql_connect() call, but had to use mysql_real_connect() which has many more parameters. To complicate things further, the number of parameters seems to have changed between version3 (where there are seven) and version4 (where there are eight). Before using mysql_real_connect I had to use mysql_init() which is not found in the original mysql.pp but is found in mysql_v4.pp.

Note added in July 2011: There have been several updates to the version of MySQL, and the current release in most distributions is version 5.1. Several pages in the wiki refer to version 5.0, and there are statements in several places that version 5.1 doesn't work, or that you still need to use the 5.0 libraries. However, recent SVN versions of FPC and Lazarus contain all the proper connections for MySQL 5.1.

So the code for connection to the database is now:

<delphi>{ a few extra variables} var

 alloc : PMYSQL;
 

{main program fragment}

begin

 if paramcount=1 then
 begin
   Dummy:=Paramstr(1)+#0;
   DataBase:=@Dummy[1];
 end;
 
 Writeln('Allocating Space...');
 alloc := mysql_init(PMYSQL(@qmysql));
 Write('Connecting to MySQL...');
 sock := mysql_real_connect(alloc, host, user, passwd, database, 0, nil, 0);
 if sock=Nil then
 begin
   Writeln(stderr,'Couldnt connect to MySQL.');
   Writeln(stderr, 'Error was: ', mysql_error(@qmysql));
   halt(1);
 end;
 Writeln('Done.');
 Writeln('Connection data:');
{$ifdef Unix}
 writeln('Mysql_port      : ',mysql_port);
 writeln('Mysql_unix_port : ',mysql_unix_port);
{$endif}
 writeln('Host info       : ',mysql_get_host_info(sock));
 writeln('Server info     : ',mysql_stat(sock));
 writeln('Client info     : ',mysql_get_client_info);
 
 Writeln('Selecting Database ',DataBase,'...');
 if mysql_select_db(sock, DataBase) < 0 then
 begin
   Writeln(stderr,'Couldnt select database ',Database);
   Writeln(stderr,mysql_error(sock));
   halt(1);
 end;
{... as original contents of testdb.pp}</delphi>

Now - ready to start compiling trydb.pp?

 fpc trydb

success! Now run it:

 ./trydb

whoopee! I got the listing of the FPC developers!

A few extra refinements: make the entry of user details and the mysql commands interactive, using variables rather than constants, and allow several SQL commands to be entered, until we issue the quit command: see the full program listing, where user details are entered from the console, and the program goes into a loop where SQL commands are entered from the console (without the terminal semicolon) and the responses are printed out, until 'quit' is entered from the keyboard.

See Sample Console Listing.

Connecting to MySQL from a Lazarus Application

This tutorial shows how to connect Lazarus to the MySQL database, and execute simple queries, using only the basic Lazarus components; it uses no Data Aware components, but illustrates the principles of interfacing with the database.

Create a new project in Lazarus:

Project -> New Project -> Application

A new automatically generated Form will appear.

Enlarge the form to fill about half of the screen, then re-name the form and its caption to 'TryMySQL'.

From the Standard Component tab place three Edit Boxes on the upper left side of the Form, and immediately above each box place a label. Change the names and captions to 'Host' (and HostLLabel,HostEdit), 'UserName' (and UserLabel, UserEdit) and 'Password' (with PasswdLabel and PasswdEdit). Alternatively you could use LabelledEdit components from the Additional tab.

Select the Passwd Edit box and find the PasswordChar property: change this to * or some other character, so that when you type in a password the characters do not appear on your screen but are echoed by a series of *s. Make sure that the Text property of each edit box is blank.

Now place another Edit box and label at the top of the right side of your form. Change the label to 'Enter SQL Command' and name it CommandEdit.

Place three Buttons on the form: two on the left under the Edit boxes, and one on the right under the command box.

Label the buttons on the left 'Connect to Database' (ConnectButton)and 'Exit' (ExitButton) and the one on the right 'Send Query' (QueryButton).

Place a large Memo Box labelled and named 'Results' (ResultMemo) on the lower right, to fill most of the available space. Find its ScrollBars property and select ssAutoBoth so that scroll bars appear automatically if text fills the space. Make the WordWrap property True.

Place a Status Bar (from the Common Controls tab) at the bottom of the Form, and make its SimpleText property 'TryMySQL'.

A screenshot of the Form can be seen here: Mysql Example Screenshot

Now we need to write some event handlers.

The three Edit boxes on the left are for entry of hostname, username and password. When these have been entered satisfactorily, the Connect Button is clicked. The OnCLick event handler for this button is based on part of the text-mode FPC program above.

The responses from the database cannot now be written using the Pascal write or writeln statements: rather, the replies have to be converted into strings and displayed in the Memo box. Whereas the Pascal write and writeln statements are capable of performing a lot of type conversion 'on the fly', the use of a memo box for text output necessitates the explicit conversion of data types to the correct form of string, so Pchar variables have to be converted to strings using StrPas, and integers have to be converted with IntToStr.

Strings are displayed in the Memo box using

<delphi>procedure ShowString(S : string); (* display a string in a Memo box *) begin

 trymysqlForm1.ResultsMemo.Lines.Add(S)

end;</delphi>

The ConnectButton event handler thus becomes:

<delphi>procedure TtrymysqlForm1.ConnectButtonClick(Sender: TObject); (* Connect to MySQL using user data from Text entry boxes on Main Form *) var strg: string;

begin

 dummy1 :=  trymysqlForm1.HostEdit.text+#0;
 host := @dummy1[1];
 dummy2 := trymysqlForm1.UserEdit.text+#0;
 user := @dummy2[1] ;
 dummy3 := trymysqlForm1.PasswdEdit.text+#0;
 passwd := @dummy3[1] ;
 alloc := mysql_init(PMYSQL(@qmysql));
 sock :=  mysql_real_connect(alloc, host, user, passwd, database, 0, nil, 0);
 if sock=Nil then
   begin
     strg :='Couldnt connect to MySQL.'; showstring (strg);
     Strg :='Error was: '+ StrPas(mysql_error(@qmysql)); showstring (strg);
   end
   else
   begin
     trymysqlForm1.statusBar1.simpletext := 'Connected to MySQL';
     strg := 'Now choosing database : ' + database; showstring (strg);
{$ifdef Unix}
     strg :='Mysql_port      : '+ IntToStr(mysql_port); showstring (strg);
     strg :='Mysql_unix_port : ' + StrPas(mysql_unix_port); showstring (strg);
{$endif}
     Strg :='Host info       : ' + StrPas(mysql_get_host_info(sock));
     showstring (strg);
     Strg :='Server info     : ' + StrPas(mysql_stat(sock)); showstring (strg);
     Strg :='Client info     : ' + Strpas(mysql_get_client_info);  showstring (strg);
 
     trymysqlForm1.statusbar1.simpletext := 'Selecting Database ' + DataBase +'...';
     if mysql_select_db(sock,DataBase) < 0 then
     begin
       strg :='Couldnt select database '+ Database; ShowString (strg);
       Strg := mysql_error(sock); ShowString (strg);
     end
   end;

end;</delphi>

The Text Box on the right allows entry of a SQL statement, without a terminal semicolon; when you are satisfied with its content or syntax, the SendQuery button is pressed, and the query is processed, with results being written in the ResultsMemo box.

The SendQuery event handler is again based on the FPC text-mode version, except that once again explicit type-conversion has to be done before strings are displayed in the box.

A difference from the text-mode FPC program is that if an error condition is detected, the program does not halt and MySQL is not closed; instead, control is returned to the main form and an opportunity is given to correct the entry before the command is re-submitted. The application finally exits (with closure of MySQL) when the Exit Button is clicked.

The code for SendQuery follows:

<delphi>procedure TtrymysqlForm1.QueryButtonClick(Sender: TObject); var

 dumquery, strg: string;

begin

 dumquery := TrymysqlForm1.CommandEdit.text;
 dumquery := dumquery+#0;
 query := @dumquery[1];
 trymysqlForm1.statusbar1.simpletext := 'Executing query : '+ dumQuery +'...';
 strg := 'Executing query : ' + dumQuery; showstring (strg);
 if (mysql_query(sock,Query) < 0) then
 begin
   Strg :='Query failed '+ StrPas(mysql_error(sock)); showstring (strg);
 end
 else
 begin
   recbuf := mysql_store_result(sock);
   if RecBuf=Nil then
   begin
     Strg :='Query returned nil result.'; showstring (strg);
   end
   else
   begin
     strg :='Number of records returned  : ' + IntToStr(mysql_num_rows (recbuf));
     Showstring (strg);
     Strg :='Number of fields per record : ' + IntToStr(mysql_num_fields(recbuf));
     showstring (strg);
     rowbuf := mysql_fetch_row(recbuf);
     while (rowbuf <>nil) do
     begin
       Strg :='(Id: '+ rowbuf[0]+', Name: ' + rowbuf[1]+ ', Email : ' +
       rowbuf[2] +')';
       showstring(strg);
       rowbuf := mysql_fetch_row(recbuf);
     end;
   end;
 end;

end;</delphi>

Save your Project, and press Run -> Run

Download MYSQL Source Code

A full listing of the program is available here Sample Source Code

Lazarus, MySQL and UTF-8

The following may be required for other codepages/character sets as well

UTF-8 Unicode is a convenient multibyte character set encoding, that allows working with multilingual texts without requiring WideStrings. It is supported both by Lazarus SQLdb components and by MySQL since version 4.1 by choosing the appropriate character set.

However, simply setting this encoding as default for your tables and MySQL Connection component will result in incorrect storage and retrieval of utf-8 strings, when any accented/international character will show up as question mark (?). Apparently, the reason for this is that MySQL client library is compiled to expect Latin1 character set by default.

In order to enable proper communication between Lazarus, MySQL client library and MySQL server, additional two queries need to be executed each time a connection to the database is established: <sql>SET CHARACTER SET `utf8`</sql> and <sql>SET NAMES 'utf8'</sql> The first query will ensure your application receives strings in correct encoding, and the second tells MySQL not to convert strings it receives from your application.

Simple MySQL Demo Using the TMySQL50Connection Component

Here is code that functions as a quick demo to get up and running simply (tested on Win XP with Lighty2Go, though xampp would be just as suitable). libmysql.dll was put in the project and lazarus.exe directories (available from a directory in Lighty2Go or xampp - but ensure that you use the correct version of libmysql.dll to match the chosen TMySQL5xxConnection Component - for TMySQL50Connection use the version for MySQL 5.0 (1484kB) and this can connect fine to both MySQL 5.0 and MySQL 5.1 DBMSs. The 5.1 version of libmysql.dll will not function with TMySQL50Connection).

A component for connection to MySQL 5.1 is now found in the SVN versions of Lazarus trunk and FPC, which certainly functions without problems using MySQL 5.1 libraries in Linux.

There is no requirement to place any components on the form other than the three edit boxes, a memo box and a few buttons. You need to add mysqlXXconn and sqldb to the uses statement. The Lazarus component directory must be rw for the programmer. The mysql dbms here has a user 'root' with no password, and a database test1 with table tPerson which has three fields: personid (int), surname (varchar(40)) and dob (datetime). phpMyAdmin (in Lighty2Go) was used to create the db, table and fields and insert some sample data. Note that dates in phpMyAdmin should be entered YYYY-MM-DD, though the program created below will accept dates in the usual formats. The button btnTest must be clicked first as it creates the connection with the dbms. Note the line that applies updates - without this the changed or new data will not be written back to the db though they will be in memory and can be viewed using btnFirst and btnNext.

<delphi>unit unt_db; // Example based on: // http://www.lazarus.freepascal.org/index.php?name=PNphpBB2&file=viewtopic&t=5761 // from tpglemur on that forum {$mode objfpc}{$H+} interface uses

 Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs,
 mysql50conn, sqldb, StdCtrls;

type

 { TForm1 }
 TForm1 = class(TForm)
   btnTest: TButton;
   btnNext: TButton;
   btnFirst: TButton;
   btnNew: TButton;
   edtPersonID: TEdit;
   edtSurname: TEdit;
   edtDOB: TEdit;
   Memo1: TMemo;
   procedure btnFirstClick(Sender: TObject);
   procedure btnNewClick(Sender: TObject);
   procedure btnNextClick(Sender: TObject);
   procedure btnTestClick(Sender: TObject);
 private
   { private declarations }
   conn : TMySQL50Connection;
   query : TSQLQuery;
   transaction : TSQLTransaction;
   procedure Display;
 public
   { public declarations }
 end;

var

 Form1: TForm1;

implementation { TForm1 } procedure TForm1.btnTestClick(Sender: TObject); var

 S: String;

begin

 conn := TMySQL50Connection.Create(nil);
 query := TSQLQuery.Create(nil);
 transaction := TSQLTransaction.Create(nil);
 try
   try
     conn.HostName := '127.0.0.1';
     conn.UserName := 'root';
     conn.Password := ;
     conn.DatabaseName := 'test1';
     conn.Connected := True;
     conn.Transaction := transaction;
     query.DataBase := conn;
     //query.ParseSQL := true; //line not needed - this is the default anyway
     //query.ReadOnly := false; //line not needed - this is the default anyway
     query.SQL.Text := 'select * from tperson';
     query.Open;
     query.Last;
     S := IntToStr(query.RecordCount) + #13#10;
     query.First;
     while not query.EOF do
     begin
       S := S + query.FieldByName('surname').AsString + #13#10;
       query.Next;
     end;
   finally
     //query.Free;
     //conn.Free;
   end;
 except
   on E: Exception do
     ShowMessage(E.message);
 end;
 Memo1.Text:= S;

end;

procedure TForm1.Display; begin

 edtPersonID.Text := query.FieldByName('personid').AsString;
 edtSurname.Text := query.FieldByName('surname').AsString;
 edtDOB.Text := query.FieldByName('dob').AsString;

end;

procedure TForm1.btnFirstClick(Sender: TObject); begin

 query.First;
 Display;

end;

procedure TForm1.btnNewClick(Sender: TObject); begin

 query.Append;
 query.FieldValues['personid'] := edtPersonID.Text;
 query.FieldValues['surname'] := edtSurname.Text;
 query.FieldValues['dob'] := edtDOB.Text;
 query.Post;  
 query.ApplyUpdates; //to apply update
 //transaction.Commit; //line not needed

end;

procedure TForm1.btnNextClick(Sender: TObject); begin

 query.Next;
 Display;

end;

initialization

 {$I unt_db.lrs}

end.</delphi>

Here is a version using the TMySQL50Connection, TSQLQuery, TSQLTransaction, TDatasource and TDBGrid components that have been placed on the form:

<delphi>unit unt_mysql2; {$mode objfpc}{$H+} interface uses

 Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs,
 mysql50conn, sqldb, StdCtrls, db, DBGrids, DbCtrls;

type

 { TForm1 }
 TForm1 = class(TForm)
   btnConnect: TButton;
   btnSave: TButton;
   btnNext: TButton;
   btnPrior: TButton;
   Datasource1: TDatasource;
   DBGrid1: TDBGrid;
   Memo1: TMemo;
   MySQL50Connection1: TMySQL50Connection;
   SQLQuery1: TSQLQuery;
   SQLTransaction1: TSQLTransaction;
   procedure btnConnectClick(Sender: TObject);
   procedure btnNextClick(Sender: TObject);
   procedure btnPriorClick(Sender: TObject);
   procedure btnSaveClick(Sender: TObject);
   procedure FormClose(Sender: TObject; var CloseAction: TCloseAction);
   procedure FormCreate(Sender: TObject);
 private
   { private declarations }
 public
   { public declarations }
 end; 

var

 Form1: TForm1; 

implementation { TForm1 }

procedure TForm1.FormCreate(Sender: TObject); begin

 //Set properties of components:
 //(could be done in the Object Inspector)
 MySQL50Connection1.HostName := '127.0.0.1';
 MySQL50Connection1.UserName := 'root';
 MySQL50Connection1.Password := ;
 MySQL50Connection1.DatabaseName := 'test1';
 MySQL50Connection1.Transaction := SQLTransaction1;
 //SQLQuery1.ParseSQL := true; //line not needed - this is the default
 //SQLQuery1.ReadOnly := false; //line not needed - this is the default
 SQLQuery1.SQL.Text := 'select * from tperson';
 SQLQuery1.Transaction := SQLTransaction1;
 SQLQuery1.UpdateMode := upWhereChanged;
 Datasource1.Dataset := SQLQuery1;
 DBGrid1.DataSource := Datasource1;;

end;

procedure TForm1.btnConnectClick(Sender: TObject); var

S : string;

begin

 try
   MySQL50Connection1.Connected := true;
   SQLQuery1.Open;
   //Tests to see if all is OK:
   SQLQuery1.Last;
   S := IntToStr(SQLQuery1.RecordCount) + #13#10;
   SQLQuery1.First;
   while not SQLQuery1.EOF do
   begin
     S := S + SQLQuery1.FieldByName('surname').AsString + #13#10;
     SQLQuery1.Next;
   end;
 except
   on E: Exception do
     ShowMessage(E.message);
 end;
 Memo1.Text:= S;

end;

procedure TForm1.btnNextClick(Sender: TObject); begin

 SQLQuery1.Next;

end;

procedure TForm1.btnPriorClick(Sender: TObject); begin

 SQLQuery1.Prior;

end;

procedure TForm1.btnSaveClick(Sender: TObject); begin

 SQLQuery1.ApplyUpdates;

end;

procedure TForm1.FormClose(Sender: TObject; var CloseAction: TCloseAction); begin

 //Required or get EDatabase error on close:
 MySQL50Connection1.Connected := false;

end;

initialization

 {$I unt_mysql2.lrs}

end.</delphi>

Lazarus and PostgreSQL

This is a very short tutorial to get Lazarus 0.9.12 or later to connect to a PostgreSQL database, local or remote, using TPQConnection. This component is added to Lazarus when the package lazarus/components/sqldb/sqldblaz.lpk is installed.

After correct install, follow these steps:

  • Place a PQConnection from the SQLdb tab
  • Place a SQLQuery from the SQLdb tab
  • Place a SQLTransaction from the SQLdb tab
  • Place a DataSource from the DataAccess tab
  • Place a DBGrid from the DataControls tab
  • In the PQConnection fill in:
    • transaction property with the respective SQLTransaction object
    • Database name
    • HostName
    • UserName + password
  • Check that the SQLTransaction was automatically changed to point to the PQConnection
  • In the SQLQuery fill in:
    • transaction property with the respective object
    • database property with respective object
    • SQL (something like 'select * from anytable')
  • In the DataSource object fill in the DataSet property with the SQLQuery object
  • In the DBGrid fill in the datasource as the DataSource Object

Turn everything to connected and active and the DBGrid should be filled in design time. TDBText and TDBEdit seem to work but (for me) they only _show_ _data_.

To change contents in the database, I called the DB Engine direct with the following code:

<delphi>try

 sql:= 'UPDATE table SET setting=1';
 PQDataBase.Connected:=True;
 PQDataBase.ExecuteDirect('Begin Work;');
 PQDataBase.ExecuteDirect(sql);
 PQDataBase.ExecuteDirect('Commit Work;');
 PQDataBase.Connected:=False;

except

 on E : EDatabaseError do
   MemoLog.Append('DB ERROR:'+sql+chr(13)+chr(10)+E.ClassName+chr(13)+chr(10)+E.Message);
 on E : Exception do
   MemoLog.Append('ERROR:'+sql+chr(13)+chr(10)+E.ClassName+chr(13)+chr(10)+E.Message);

end;</delphi>

  • Notes:
    • Tested on windows, Lazarus 0.9.12 + PgSQL 8.3.1
    • Some tests in linux, Lazarus 0.9.12 and PgSQL 8.0.x


  • Instalation and errors:
    • In the tested version of Lazarus .12, fields of type "text" and "numeric" have bugs
    • I used with no problems char fixed size, int and float8
    • Sometimes restarting Lazarus solves stupid errors...
    • After some errors, the transactions remain active and should be deactivated mannually
    • Changes made in Lazarus are of course not visible until transaction commited
    • The integrated debugger seems buggy (at least in windows) - sometimes running outside of the IDE may help to find errors
    • In linux certain error messages are printed in the console -- run your program in the command line, sometimes there is some extra useful debugging info
    • Error: "Can not load Postgresql client. Is it installed (libpq.so) ?"
      • Add the path to seach libpq* from the PostgreSQL installation.
      • In linux add the path to the libpq.so file to the libraries section in your /etc/fpc.cfg file. For example : -Fl/usr/local/pgsql/lib
      • It may be necessary to create a symboloic link ln -s /usr/lib/pqsql.so.5 /usr/lib/pqsql.so
      • In windows, add these libs anywhere in the Path environment variable or project dir
      • I windows, I copied all the DLLs in my C:\Program Files\PostgreSQL\8.1\bin dir to another dir in the PATH
      • Or add this postgres\bin dir to the path

A good example about connecting Lazarus with PostgreSQL under Windows is easyDB.

Lazarus and SQLite

Using the TSQLite3Dataset

by Luiz Américo

WARNING: this section is about the sqlite components that are shipped with Free Pascal distribution (TSqliteDataset and TSqlite3Dataset). Free Pascal also provides access to sqlite through Sqldb (also in the default distribution), Zeos and SqlitePass components.

Visit the sqlite4fpc homepage to find the API reference and more tutorials.

Introduction

TSqliteDataset and TSqlite3Dataset are TDataset descendants that access, respectively, 2.8.x and 3.x.x sqlite databases. Below is a list of the principal advantages and disadvantages:

Advantages:

  • Flexible: programmers can choose to use or not to use the SQL language, allowing them to work with simple table layouts or any complex layout that SQL/sqlite allows
  • Automatic database update: no need to update the database manually with SQL statements, a single method take cares of it
  • Fast: it caches the data in memory, making browsing in the dataset fast
  • No server installation/configuration: just ship together with sqlite dynamic library

Disadvantages

  • Requires external file (sqlite library)

Requirements

  • For sqlite2 databases:
    • fpc 2.0.0
    • Lazarus 0.9.10
    • sqlite runtime library 2.8.15 or above*
  • Sqlite2 is not maintained anymore and the binary file cannot be found in the sqlite site
  • For sqlite3 databases:
    • fpc 2.0.2
    • Lazarus 0.9.11 (svn revision 8443 or above)
    • sqlite runtime library 3.2.1 or above (get from www.sqlite.org)

Before initiating a lazarus projects, ensure that:

  • the sqlite library is on the system PATH or in the executable directory
  • under Linux, put cmem as the first unit in uses clause of the main program
    • In Debian, Ubuntu and other Debian-like distros, in order to build Lazarus IDE you must install the packages libsqlite-dev/libsqlite3-dev, not only sqlite/sqlite3 (Also applies to OpenSuSe)

How To Use (Basic Usage)

Install the package found at /components/sqlite directory (see instructions here)

At design time set the following properties:

  • FileName: path of the sqlite file [required]
  • TableName: name of the table used in the sql statement [required]
  • Sql: a SQL select statement [optional]
  • SaveOnClose: The default value is false, which means that changes are not saved. One can change it to True. [optional]
  • Active: Needs to be set at design time or at program startup. [required]

Creating a Table (Dataset)

Double click in the component icon or use the 'Create Table' item of the popup menu that appears when clicking the right mouse button. A simple self-explaining table editor will be show.

Here is all field types supported by TSqliteDataset and TSqlite3Dataset:

  • Integer
  • AutoInc
  • String
  • Memo
  • Bool
  • Float
  • Word
  • DateTime
  • Date
  • Time
  • LargeInt
  • Currency

Retrieving the data

After creating the table or with a previously created Table, open the dataset with Open method. If the SQL property was not set then all records from all fields will be retrieved, the same if you set the SQL to:

<delphi>SQL := 'Select * from TABLENAME';</delphi>

Applying changes to the underlying datafile

To use the ApplyUpdates function, the dataset must contain at least one field that fills the requirements for a Primary Key (values must be UNIQUE and not NULL)

It's possible to do that in two ways:

  • Set PrimaryKey property to the name of a Primary Key field
  • Add an AutoInc field (This is easier since the TSqliteDataSet automatically handles it as a Primary Key)

If one of the two conditions is set then just call

<delphi>ApplyUpdates;</delphi>

PS1: If both conditions are set, the field corresponding to PrimaryKey is used to apply the updates.

PS2: Setting PrimaryKey to a field that is not a Primary Key will lead to loss of data if ApplyUpdates is called, so ensure that the chosen field contains not Null and Unique values before using it.

Remarks

  • Although it has been tested with 10000 records and worked fine, TSqliteDataset keeps all the data in memory, so remember to retrieve only the necessary data (principally with Memo Fields).
  • The same datafile (Filename property) can host several tables/datasets
  • Several datasets (different combinations of fields) can be created using the same table simultaneously
  • It's possible to filter the data using WHERE statements in the sql, closing and reopening the dataset (or calling RefetchData method). But in this case, the order and number of fields must remain the same
  • It's also possible to use complex SQL statements using aliases, joins, views in multiple tables (remember that they must reside in the same datafile), but in this case ApplyUpdates won't work. If someone wants to use complex queries and to apply the updates to the datafile, mail me and i will give some hints how to do that
  • Setting filename to a sqlite datafile not created by TSqliteDataset and opening it is allowed but some fields won't have the correct field type detected. These will be treated as string fields.

Generic examples can be found at fpc/fcl-db/src/sqlite SVN directory

Luiz Américo luizmed(at)oi(dot)com(dot)br TSQLite3Connection


Using the SQLdb components with TSQLIte3Connection

To use these components we will replace the TQLite3Dataset from the previous example with a combination of three components from the SQLdb tab: TSQLite3Connection, TSQLTransaction and TSQLQuery (the TSQLQuery is the one that is now acting as our TDataset, in the simplest case it just represents one of our tables). For the sake of simplicity I assume you already have an existing sqlite database file and don't need to create a new one one now. You should also have a look at this SqlDBHowto which also has some useful information about the SQLdb components.

The three components are connected with each other as usual: In the TSQLQuery set the properties Database and Transaction, in the TSQLTransaction set the property Database. There is not much to do in the Transaction and Connection components, most interesting stuff will be done in the TSQLQuery. Configure the components as follows:

TSQLite3Connection:

  • DatabaseName: Set this property to the file name (absolute path!) of your SQLite file. Unfortunately you cannot simply use a relative path that works unchanged at designtime and at runtime. You should make sure that at application start the correct path to the file is always set programmatically, no matter what it contained at designtime.

TSQLQuery:

  • SQL: Set it to some simple select query on one of your tables. For example if you have a table 'foo' and want this Dataset to represent this table then just use the following: SELECT * FROM foo
  • Active: Set this to True from within the IDE to test whether it is all set up correctly. This will also automatically activate the transaction and the connection objects. If you receive an error then either the DatabaseName of the connection is not correct or the SQL query is wrong (remember: I assumed for simplicity that you already have an existing SQLite database with tables in it). Later if we are done adding the fields (see below) set them all to inactive again, we don't want the IDE to lock the SQLite database (single user!) when testing the application.
  • Now we can add Fields to our TSQLQuery. While the components are still set to active do a right click and "edit fields...". Click the "+" button and add fields. It will list all fields your SQL query returned. Add every field you will need, you can also add lookup fields here, in this case just make sure you have already defined all needed fields in the other datasets before you start adding lookup fields that refer to them. If your table has many columns and you don't need them all you can just leave them away, you can also make your SQL a bit more specific.
  • In your code you need to call SQLQuery.ApplyUpdates and SQLTransaction.Commit, TSQLQuery.AfterPost and AfterInsert events are a good place for this when using it with data aware controls but of course you can also postpone these calls to a later time. If you don't call them it will not update the database.
  • "Database is locked": SQLite is an embedded single user database. Once you are done defining all the fields of your query objects set all objects at design time to inactive again before you run your Application. Use the Form's OnCreate event to set the path and activate the objects at runtime. If you have more than one TSQLQuery and have lookup fields defined then be sure to activate them in the correct order. Most of the things you set in the TSQLQuery from within the IDE don't require them to be active at design time, the only exception is defining the fields where it needs to read the table design, so inactive at design time should be the normal state.
  • Your tables should all have a primary key and you must make sure that the corresponding field has pfInKey and nothing else in its PoviderFlags (these flags control how and where the field is used when automatically constructing the update and delete queries).
  • If you are using lookup fields
    • make sure the ProviderFlags for the lookup field is completely empty so it won't attempt to use it's name in an update query. The lookup field itself is not a data field, it only acts on the value of another field, the corresponding key field, and only this key field will later be used in the update queries. You can set the key field to hidden because usually you don't want to see it in your DBGrid but it needs to be defined.
    • LookupCache must be set to True. At the time of this writing for some reason the lookup field will not display anything otherwise (but still work) and strangely the exact opposite is the case when working with the TSQLite3Dataset or other TXXXDataset components, here it must be set to False. I'm not yet sure whether this is intended behavior or a bug.
  • Usually with simple tables you won't need to set any of the InsertSQL, UpdateSQL and DeleteSQL properties, just leave them empty. If you have the ProviderFlags of all your fields set correctly it should be able to create the needed SQL on the fly. An example for an update query would be UPDATE foo SET bar=:bar,baz=:baz WHERE id=:id; The placeholders start with : and refer to the Name properties of the TField objects. You need to set these queries manually when your dataset is composed of more complex SQL from multiple tables where it cannot figure out on its own how to correctly update the underlying data.

After the above is all set up correctly you should now be able to use the TSQLQuery like any other TDataset, either by manipulating it's data programmatically or by placing a TDatasouce on the Form, connecting it to the TSQLQuery and then using data contols like TDBGrid etc.

Lazarus and MSSQL

It is working with Zeoslib (latest cvs), see the links on bottom of page.

Alternatively you can access MSSQL databases via ODBC - no need to install Zeoslib or any other additional libraries - just use the SQLdb component that is included (I tested this in Lazarus v0.9.26.2)

The example code below selects the rows from a table called 'journal_entries' and displays all the values of column 'journal_entry' in a Memo control called Memo1.

<delphi>procedure TForm1.Button1Click(Sender: TObject); var

 S: String;
 conn: TODBCConnection;
 query: TSQLQuery;
 transaction: TSQLTransaction;

begin

 conn := TODBCCOnnection.Create(nil);
 query := TSQLQuery.Create(nil);
 transaction := TSQLTransaction.Create(nil);
 try
   try
     conn.HostName := '127.0.0.1';
     conn.DatabaseName := 'diary'; {replace this with the name of your database}
     conn.Transaction := transaction;
     conn.UserName:= 'db_username';
     conn.Password:= ;
     query.DataBase := conn;
     { The following line is required, else you get "could not retrieve primary key metadata".
       I was really stuck on this until I found http://bugs.freepascal.org/view.php?id=13241 }
     query.UsePrimaryKeyAsKey:=false; 
     query.SQL.Text := 'select * from diary.dbo.journal_entries';
     query.Open; 
     S := ;
     while not query.EOF do
     begin
       S := S + query.FieldByName('journal_entry').AsString + #13#10;
       query.Next;
     end;
   finally
     query.Free;
     conn.Free;
   end;
 except
   on E: Exception do
     ShowMessage(E.message);
 end;
 Memo1.Text:= S;

end;</delphi>

Lazarus and Interbase / Firebird

Built-in support (SQLDB components)

See these tutorials/tips pages:

See also Install Packages. On this page is a first small example en explanation about how to connect to an IB or FB server.

Zeos

Firebird also works with the latest Zeos data access library (from cvs).

FBLib Firebird Library

FBLib is an open source library, for direct access to Firebird Relational Database from Borland Delphi, Kylix, Free Pascal and Lazarus.

Current Features include:

  • Direct Access to Firebird 1.0.x 1.5.x, 2.x Classic or SuperServer
  • Multi platform [Win32,Gnu/Linux,FreeBSD)
  • Automatic select client library 'fbclient' or 'gds32'
  • Query with params
  • Support SQL Dialect 1/3
  • LGPL License agreement
  • Extract Metadata
  • Simple Script Parser
  • Only 100-150 KB added into final EXE
  • Support BLOB Fields
  • Export Data to HTML SQL Script
  • Service manager (backup,restore,gfix...)
  • Events Alerter

You can download documentation on FBLib's website.

Here you can find a updated version. Or, use the svn: [1] (Tip by Guionardo)

Lazarus and dBase

Tony Maro

You might also want to visit the TDbf Tutorial page

FPC includes a simple database component that is similar in function to the Delphi TTable component called "TDbf" (TDbf Website) that supports a subset of features for dBase files. It is not installed by default, so you will first need to install the Lazarus package from the "lazarus/components/tdbf" directory and rebuild your Lazarus IDE. It will then appear next to the TDatasource in your component palette (Data Access tab).

The TDbf component has an advantage over other database components in that it doesn't require any sort of runtime database engine. However it's not the best option for large database applications.

It's very easy to use. Simply drop a TDbf on your form, set the runtime path to the directory that your database files will be in, set the table name, and link it to your TDatasource component.

Real functionality requires a bit more effort, however. If a table doesn't already exist, you'll need to create it programmatically, unless there's a compatible table designer I'm not familiar with. Note: Current version of OpenOffice/LibreOffice (3.x) contains OpenOffice Base, which can create dbf files in a somewhat user-friendly way.

Attempting to open a nonexistent table will generate an error. Tables can be created programmatically through the component after the runtime path and table name are set.

For instance, to create a table called "dvds" to store your DVD collection you would drop it on your form, set the runtime path, and set the table name to "dvds". The resulting file will be called "dvds.dbf".

In your code, insert the following:

<delphi>Dbf1.FilePathFull := '/path/to/my/database'; Dbf1.TableName := 'dvds'; With Dbf1.FieldDefs do begin

 Add('Name', ftString, 80, True);
 Add('Description', ftMemo, 0, False);
 Add('Rating', ftString, 5, False);

end; Dbf1.CreateTable;</delphi>

When this code is run, your DVD collection table will be created. After that, all data aware components linked through the TDatasource to this component will allow easy access to the data.

Adding an index is a little different from your typical TTable. It must be done after the database is open. You use the same method also to rebuild the indices. For instance:

<delphi>Dbf1.Exclusive := True; Dbf1.Open; Dbf1.AddIndex('dvdsname','Name',[ixPrimary, ixUnique, ixCaseInsensitive]); Dbf1.AddIndex('rating.ndx', 'Rating', [ixCaseInsensitive]); Dbf1.Close;</delphi>

The first (primary) index will be a file called "dvdsname.mdx" and the second will be a file named "rating.ndx" so in a multiple table database you must be careful not to use the same file name again.

Please see TDbf Tutorial page for more details, but hopefully this will get those old Delphi programmers up and running with databases in Lazarus!

Searching and Displaying a data set

Simon Batty

In this example I wanted to search a database of books for all the titles an author has listed and then display the list in a memo box <delphi>Dbf1.FilePathFull := '/home/somelocatio/database_location/'; // path to the database directory Dbf1.TableName := 'books.dbase'; // database file (including extension) DbF1.Open; memo1.Clear; // clear the memo box

Dbf1.FilterOptions := [foCaseInsensitive]; Df1.Filter := 'AU=' + QuotedStr('anauthor'); // AU is the field name containing the authors

Dbf1.Filtered := true; // This selects the filtered set Dbf1.First; // moves the the first filtered data while not dbf1.EOF do // prints the titles that match the author to the memo box begin

 memo1.Append(Dbf1.FieldByName('TI').AsString); // TI is the field name for titles
 dbf1.next;                                     // use .next here NOT .findnext!

end; Dbf1.Close;</delphi>

Note that you can use Ddf1.findfirst to get the first record in the filtered set, then use Dbf1.next to move though the data. I found that using Dbf1.Findnext just causes the program to hang.

This database was generated using TurboBD that came with the Kylix 1. I cannot get TurboBD tables to work with Lazarus, however you can download a command line tool from TurboDB's website that allows you to convert TurboDB table to other formats.

Using TSdfDataset and TFixedDataset

TSdfDataset and TFixedDataset are two simple datasets which offer a very simple textual storage format. These datasets are very convenient for small databases, because they are fully implemented as an object pascal unit, and thus require no external libraries, and because their textual format allows them to be easely edited with a text editor.

To start with this formats, a initial database file should be created. The format is very simple, so use a text editor to do this.

Bellow is a sample database for TSdfDataset. Note that the first line has the names of the fields and that we are using commas as separators:

ID,NAMEEN,NAMEPT,HEIGHT,WIDTH,PINS,DRAWINGCODE
1,resistor,resistor,1,1,1,LINE
2,capacitor,capacitor,1,1,1,LINE
3,transistor npn,transistor npn

And here is an example database for using with TFixedDataset. Each record occupies a fixed amount of space, and if the field is smaller then it, spaces should be used to fill the remaining size.

Name = 15 chars; Surname = 15 chars; Tell = 10 chars; e_mail = 20 chars;
Piet           Pompies                  piet@pompies.net

Using the datasets directly

Sometimes it is useful to create the dataset and work with it completely in code, and the following code will do exactly this. Note some peculiarities of TSdfDataset/TFixedDataset:

  • The lines in the database can have a maximum size of about 300. A fix is being researched.
  • It is necessary to add the field definitions. Some datasets are able to fill this information alone from the database file
  • One should set FirstLineAsSchema to true, to indicate that the first line includes the field names and positions
  • The Delimiter property holds the separator for the fields. It will not be possible to use this char in strings in the database. Similarly it will not be possible to have lineendings in the database because they mark the change between records. It's possible to overcome this by substituting the needed comma or line ending with another not often used char, like # for example. So that when showing the data on screen all # chars could be converted to line endings and the inverse when storing data back to the database. The ReplaceString routine is useful here.

<delphi> uses sdfdata, db;

constructor TComponentsDatabase.Create; var

 FDataset: TSdfDataset;

begin

 inherited Create;
 FDataset := TSdfDataset.Create(nil);
 FDataset.FileName := vConfigurations.ComponentsDBFile;
 // Not necessary with TSdfDataset

// FDataset.TableName := STR_DB_COMPONENTS_TABLE; // FDataset.PrimaryKey := STR_DB_COMPONENTS_ID;

 // Adds field definitions
 FDataset.FieldDefs.Add('ID', ftString);
 FDataset.FieldDefs.Add('NAMEEN', ftString);
 FDataset.FieldDefs.Add('NAMEPT', ftString);
 FDataset.FieldDefs.Add('HEIGHT', ftString);
 FDataset.FieldDefs.Add('WIDTH', ftString);
 FDataset.FieldDefs.Add('PINS', ftString);
 FDataset.FieldDefs.Add('DRAWINGCODE', ftString);
 // Necessary for TSdfDataset
 FDataset.Delimiter := ',';
 FDataset.FirstLineAsSchema := True;
 FDataset.Active := True;
 // Sets the initial record
 CurrentRecNo := 1;
 FDataset.First;

end;</delphi>

When using TSdfDataset directly be aware that RecNo, although it is implemented, does not work as a way to move through the dataset whether reading or writing records. The standard navigation routines like First, Next, Prior and Last work as expected, so you need to use them rather than RecNo. If you are used to using absolute record numbers to navigate around a database you can implement your own version of RecNo. Declare a global longint variable called CurrentRecNo which will hold the current RecNo value. Remember that this variable will have the same convention as RecNo, so the first record has number 1 (it is not zero-based). After activating the database initialize the database to the first record with TSdfDataset.First and set CurrentRecNo := 1

<delphi>{@@

 Moves to the desired record using TDataset.Next and TDataset.Prior
 This avoids using TDataset.RecNo which doesn't navigate reliably in any dataset.
 @param AID Indicates the record number. The first record has number 1

} procedure TComponentsDatabase.GoToRec(AID: Integer); begin

 // We are before the desired record, move forward
 if CurrentRecNo < AID then
 begin
   while (not FDataset.EOF) and (CurrentRecNo < AID) do
   begin
     FDataset.Next;
     FDataset.CursorPosChanged;
     Inc(CurrentRecNo);
   end;
 end
 // We are after the desired record, move back
 else if CurrentRecNo > AID  then
 begin
   while (CurrentRecNo >= 1) and (CurrentRecNo > AID) do
   begin
     FDataset.Prior;
     FDataset.CursorPosChanged;
     Dec(CurrentRecNo);
   end;
 end;

end;</delphi>

Using with data-aware controls

Lazarus and Advantage Database Server

This brief tutorial is intended to get you started using the Advantage TDataSet Descendent to access tables hosted by the Advantage Database Server.

Installing the Advantage TDataSet

Windows

If installing the Advantage TDataSet on Windows, you will need to download and install the Advantage Delphi Components (version 10.1 or greater). The install media can be obtained from the Advantage web site here.

Linux

If installing the Advantage TDataSet on Linux, you will need to complete a two-part installation. First, download and install the Advantage Client Engine for Linux (version 10.1). Second, download and extract the Linux TDataSet source tarball. Both downloads are available at the Advantage Developer Zone at http://devzone.advantagedatabase.com. (The Advantage Client Engine download is located in the "Product Download" section of the site, and the Linux TDataSet source is available in the Delphi Applications section of the CodeCentral page of the Advantage Developer Zone.)

Installing the Advantage Package

Once the TDataSet Descendant is installed, you'll want to move on to installing the package into Lazarus.

  1. From Lazarus, click on "Package", then "Open Package File (.lpk)..." and browse to the adsl.lpk file in the TDataSet installation directory (or in the directory you extracted the TDataSet source).
  2. In the package window, click the "Compile" button.
  3. Upon successful compilation, click the "Install" button, and select "Yes" to rebuild Lazarus.
  4. The Lazarus IDE should successfully compile and re-start with the Advantage components installed.

A simple Advantage project

Start a new project to start working with Advantage data.

  1. Drop a TAdsConnection object from the Advantage tab of the palette onto your form. (The TAdsConnection object is the left-most object on the Advantage tab.)
  2. In the Object Inspector, click the drop-down for the AliasName property, and select "ADTDemoData".
    • Alternately, you can select the ConnectPath property and enter (or browse to) the path to the Help\ADS_Data directory beneath your TDataSet (or acesdk on Linux) install directory.
  3. Expand the AdsServerTypes property, and change the "stADS_LOCAL" property to True.
    • If you have an Advantage Database server configured and running, you may set "stADS_REMOTE" to true instead.
  4. Drop a TAdsTable object on the form. (The TAdsTable object is immediately to the right of the TAdsConnection object on the tab, and it looks like a red table.)
  5. Set the AdsConnection Property for AdsTable1 to AdsConnection1 (the connection object you just dropped in step 1.)
  6. Scroll down to the "TableName" property, and use the drop-down box to select the biolife.adt table.
  7. Drop a TDataSource component on the form, and set its DataSet property to "AdsTable1".
  8. Drop a TDBGrid component on the form, and set its "DataSource" property to "Datasource1".
  9. At this point, you should be able to select the AdsTable1 object and set its "Active" property to "True".
  10. Finally, run the project. (Note that you may need to save the project before running it.)

Since the Advantage components descend from the TDataSet, you can use these components with any data-aware component that supports the TDataSet. This extremely simple example should demonstrate how simple it is to get started with Advantage.

See also

External links

  • Pascal Data Objects - a database API that worked for both FPC and Delphi and utilises native MySQL libraries for version 4.1 and 5.0 and Firebird SQL 1.5, and 2.0. It's inspired by PHP's PDO class.
  • Zeos+SQLite Tutorial - Good tutorial using screenshots and screencasts it explain how to use SQLite and Zeos, spanish (google translate does a good work in translating it to english)