Pascal (Lazarus/Delphi)

Using Pre-defined JSON Templates

See more JSON Examples

Demonstrates how to predefine a JSON template, and then use it to emit JSON with variable substitutions.

Note: This example requires Chilkat v9.5.0.67 or greater.

Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Hashtable,
  Chilkat.JsonObject;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  json: TJsonObject;
  jsonTemplate: TJsonObject;
  jsonDonut: TJsonObject;
  donutValues: THashtable;
  omitEmpty: Boolean;

begin
  //  One way to create JSON is to do it in a straightforward manner:
  json := TJsonObject.Create;
  json.EmitCompact := False;
  json.UpdateString('id','0001');
  json.UpdateString('type','donut');
  json.UpdateString('name','Cake');
  json.UpdateString('image.url','images/0001.jpg');
  json.UpdateInt('image.width',200);
  json.UpdateInt('image.height',200);
  json.UpdateString('thumbnail.url','images/thumbnails/0001.jpg');
  json.UpdateInt('thumbnail.width',32);
  json.UpdateInt('thumbnail.height',32);
  WriteLn(json.Emit());

  //  The JSON created by the above code:

  //  	{ 
  //  	  "id": "0001",
  //  	  "type": "donut",
  //  	  "name": "Cake",
  //  	  "image": { 
  //  	    "url": "images/0001.jpg",
  //  	    "width": 200,
  //  	    "height": 200
  //  	  },
  //  	  "thumbnail": { 
  //  	    "url": "images/thumbnails/0001.jpg",
  //  	    "width": 32,
  //  	    "height": 32
  //  	  }
  //  	}

  //  An alternative is to predefine a template, and then use it to emit with variable substitutions.
  //  For example:

  jsonTemplate := TJsonObject.Create;
  jsonTemplate.UpdateString('id','{$id}');
  jsonTemplate.UpdateString('type','donut');
  jsonTemplate.UpdateString('name','{$name}');
  jsonTemplate.UpdateString('image.url','{$imageUrl}');
  //  The "i." indicates that it's an integer variable.
  jsonTemplate.UpdateString('image.width','{$i.imageWidth}');
  jsonTemplate.UpdateString('image.height','{$i.imageHeight}');
  jsonTemplate.UpdateString('thumbnail.url','{$thumbUrl}');
  jsonTemplate.UpdateString('thumbnail.width','{$i.thumbWidth}');
  jsonTemplate.UpdateString('thumbnail.height','{$i.thumbHeight}');
  //  Give this template a name.
  jsonTemplate.Predefine('donut');

  //  --------------------------------------------------------------------------
  //  OK, the template is defined.  Defining a template can be done once
  //  at the start of your program, and you can discard the jsonTemplate object (it
  //  doesn't need to stick around..)

  //  Now we can create instances of the JSON object by name:
  jsonDonut := TJsonObject.Create;
  jsonDonut.EmitCompact := False;
  jsonDonut.LoadPredefined('donut');
  WriteLn(jsonDonut.Emit());

  //  The output is this:

  //  	{ 
  //  	  "id": "{$id}",
  //  	  "type": "donut",
  //  	  "name": "{$name}",
  //  	  "image": { 
  //  	    "url": "{$imageUrl}",
  //  	    "width": "{$i.imageWidth}",
  //  	    "height": "{$i.imageHeight}"
  //  	  },
  //  	  "thumbnail": { 
  //  	    "url": "{$thumbUrl}",
  //  	    "width": "{$i.thumbWidth}",
  //  	    "height": "{$i.thumbHeight}"
  //  	  }
  //  	}

  //  Finally, we can substitute variables like this:
  donutValues := THashtable.Create;
  donutValues.AddStr('id','0001');
  donutValues.AddStr('name','Cake');
  donutValues.AddStr('imageUrl','images/0001.jpg');
  donutValues.AddInt('imageWidth',200);
  donutValues.AddInt('imageHeight',200);
  donutValues.AddStr('thumbUrl','images/thumbnails/0001.jpg');
  donutValues.AddInt('thumbWidth',32);
  donutValues.AddInt('thumbHeight',32);

  //  Emit with variable substitutions:
  omitEmpty := True;
  WriteLn(jsonDonut.EmitWithSubs(donutValues,omitEmpty));

  //  Output:

  //  	{ 
  //  	  "id": "0001",
  //  	  "type": "donut",
  //  	  "name": "Cake",
  //  	  "image": { 
  //  	    "url": "images/0001.jpg",
  //  	    "width": 200,
  //  	    "height": 200
  //  	  },
  //  	  "thumbnail": { 
  //  	    "url": "images/thumbnails/0001.jpg",
  //  	    "width": 32,
  //  	    "height": 32
  //  	  }
  //  	}

  //  Change some of the values:
  donutValues.AddStr('id','0002');
  donutValues.AddStr('imageUrl','images/0002.jpg');
  donutValues.AddStr('thumbUrl','images/thumbnails/0002.jpg');

  WriteLn(jsonDonut.EmitWithSubs(donutValues,omitEmpty));

  //  Output:

  //  	{ 
  //  	  "id": "0002",
  //  	  "type": "donut",
  //  	  "name": "Cake",
  //  	  "image": { 
  //  	    "url": "images/0002.jpg",
  //  	    "width": 200,
  //  	    "height": 200
  //  	  },
  //  	  "thumbnail": { 
  //  	    "url": "images/thumbnails/0002.jpg",
  //  	    "width": 32,
  //  	    "height": 32
  //  	  }
  //  	}


  json.Free;
  jsonTemplate.Free;
  jsonDonut.Free;
  donutValues.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.