fpjsondataset

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Databases portal

References:

Tutorials/practical articles:

Databases

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fpjsondataset is an fcl-db unit containing a dataset class for accessing JSON data as simple table structures.


TJSONDataSet

TJSONDataSet is a dataset class for using JSON arrays for data handling.

Note-icon.png

Note: TJSONDataSet is included in Free Pascal but not visible in Lazarus' component palette.


Example

  1. Create a new application project
  2. Place a DB Grid on the form (DBGrid1)
  3. Place a DataSource on the form (DataSource1)
  4. Connect DBGrid1.Datasource with DataSource1
  5. Create a JSON dataset via code
unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, Forms, Controls, Graphics, Dialogs, DBCtrls, DBGrids, DB,
  fpjson, fpjsondataset;

type

  TForm1 = class(TForm)
    DataSource1: TDataSource;
    DBGrid1: TDBGrid;
    procedure FormCreate(Sender: TObject);
  private
    JSONDataSet: TJSONDataSet;
  end;

var
  Form1: TForm1;

const
  // this is the sample JSON data used in the demo
  JSON_STRING = '['
    +'{"Author ID":"409-56-7008","Last Name":"Bennet","First Name":"Abraham","Active": False},'
    +'{"Author ID":"213-46-8915","Last Name":"Green","First Name":"Marjorie","Active": True}'
    +']';

implementation

{$R *.lfm}

procedure TForm1.FormCreate(Sender: TObject);
var
  data: TJSONArray;
begin
  // parse the JSON string
  data := GetJSON(JSON_STRING) as TJSONArray;
  // create a new TJSONDataSet
  JSONDataSet := TJSONDataSet.Create(Self);
  // you'll need to create the FieldDefs manually
  // ftString requires a length specified
  JSONDataSet.FieldDefs.Add('Author ID', ftString, 11, True);
  JSONDataSet.FieldDefs.Add('Last Name', ftString, 40);
  JSONDataSet.FieldDefs.Add('First Name', ftString, 20);
  JSONDataSet.FieldDefs.Add('Active', ftBoolean);
  // set OwnsData to True, and the JSON data will be destroyed when the dataset is destroyed
  JSONDataSet.OwnsData := True;
  // the JSON data is an array of objects
  JSONDataSet.RowType := rtJSONObject;
  // assign the JSON data to the dataset
  JSONDataSet.Rows := data;
  // activate the dataset
  JSONDataSet.Active := True;
  // assign the dataset to the datasource
  DataSource1.DataSet := JSONDataSet;
end;

end.