(Delphi DLL) Using Pre-defined JSON Templates

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.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Hashtable, JsonObject;

...

procedure TForm1.Button1Click(Sender: TObject);
var
json: HCkJsonObject;
jsonTemplate: HCkJsonObject;
jsonDonut: HCkJsonObject;
donutValues: HCkHashtable;
omitEmpty: Boolean;

begin
// One way to create JSON is to do it in a straightforward manner:
json := CkJsonObject_Create();
CkJsonObject_putEmitCompact(json,False);
CkJsonObject_UpdateString(json,'id','0001');
CkJsonObject_UpdateString(json,'type','donut');
CkJsonObject_UpdateString(json,'name','Cake');
CkJsonObject_UpdateString(json,'image.url','images/0001.jpg');
CkJsonObject_UpdateInt(json,'image.width',200);
CkJsonObject_UpdateInt(json,'image.height',200);
CkJsonObject_UpdateString(json,'thumbnail.url','images/thumbnails/0001.jpg');
CkJsonObject_UpdateInt(json,'thumbnail.width',32);
CkJsonObject_UpdateInt(json,'thumbnail.height',32);
Memo1.Lines.Add(CkJsonObject__emit(json));

// 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 := CkJsonObject_Create();
CkJsonObject_UpdateString(jsonTemplate,'id','{$id}');
CkJsonObject_UpdateString(jsonTemplate,'type','donut');
CkJsonObject_UpdateString(jsonTemplate,'name','{$name}');
CkJsonObject_UpdateString(jsonTemplate,'image.url','{$imageUrl}');
// The "i." indicates that it's an integer variable.
CkJsonObject_UpdateString(jsonTemplate,'image.width','{$i.imageWidth}');
CkJsonObject_UpdateString(jsonTemplate,'image.height','{$i.imageHeight}');
CkJsonObject_UpdateString(jsonTemplate,'thumbnail.url','{$thumbUrl}');
CkJsonObject_UpdateString(jsonTemplate,'thumbnail.width','{$i.thumbWidth}');
CkJsonObject_UpdateString(jsonTemplate,'thumbnail.height','{$i.thumbHeight}');
// Give this template a name.
CkJsonObject_Predefine(jsonTemplate,'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 := CkJsonObject_Create();
CkJsonObject_putEmitCompact(jsonDonut,False);
CkJsonObject_LoadPredefined(jsonDonut,'donut');
Memo1.Lines.Add(CkJsonObject__emit(jsonDonut));

// 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 := CkHashtable_Create();
CkHashtable_AddStr(donutValues,'id','0001');
CkHashtable_AddStr(donutValues,'name','Cake');
CkHashtable_AddStr(donutValues,'imageUrl','images/0001.jpg');
CkHashtable_AddInt(donutValues,'imageWidth',200);
CkHashtable_AddInt(donutValues,'imageHeight',200);
CkHashtable_AddStr(donutValues,'thumbUrl','images/thumbnails/0001.jpg');
CkHashtable_AddInt(donutValues,'thumbWidth',32);
CkHashtable_AddInt(donutValues,'thumbHeight',32);

// Emit with variable substitutions:
omitEmpty := True;
Memo1.Lines.Add(CkJsonObject__emitWithSubs(jsonDonut,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:
CkHashtable_AddStr(donutValues,'id','0002');
CkHashtable_AddStr(donutValues,'imageUrl','images/0002.jpg');
CkHashtable_AddStr(donutValues,'thumbUrl','images/thumbnails/0002.jpg');

Memo1.Lines.Add(CkJsonObject__emitWithSubs(jsonDonut,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
// 	  }
// 	}

CkJsonObject_Dispose(json);
CkJsonObject_Dispose(jsonTemplate);
CkJsonObject_Dispose(jsonDonut);
CkHashtable_Dispose(donutValues);

end;