(Visual FoxPro) 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 ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loJson
LOCAL loJsonTemplate
LOCAL loJsonDonut
LOCAL loDonutValues
LOCAL lnOmitEmpty

* One way to create JSON is to do it in a straightforward manner:
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJson = CreateObject('Chilkat.JsonObject')
loJson.EmitCompact = 0
loJson.UpdateString("id","0001")
loJson.UpdateString("type","donut")
loJson.UpdateString("name","Cake")
loJson.UpdateString("image.url","images/0001.jpg")
loJson.UpdateInt("image.width",200)
loJson.UpdateInt("image.height",200)
loJson.UpdateString("thumbnail.url","images/thumbnails/0001.jpg")
loJson.UpdateInt("thumbnail.width",32)
loJson.UpdateInt("thumbnail.height",32)
? loJson.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:

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJsonTemplate = CreateObject('Chilkat.JsonObject')
loJsonTemplate.UpdateString("id","{$id}")
loJsonTemplate.UpdateString("type","donut")
loJsonTemplate.UpdateString("name","{$name}")
loJsonTemplate.UpdateString("image.url","{$imageUrl}")
* The "i." indicates that it's an integer variable.
loJsonTemplate.UpdateString("image.width","{$i.imageWidth}")
loJsonTemplate.UpdateString("image.height","{$i.imageHeight}")
loJsonTemplate.UpdateString("thumbnail.url","{$thumbUrl}")
loJsonTemplate.UpdateString("thumbnail.width","{$i.thumbWidth}")
loJsonTemplate.UpdateString("thumbnail.height","{$i.thumbHeight}")
* Give this template a name.
loJsonTemplate.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:
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJsonDonut = CreateObject('Chilkat.JsonObject')
loJsonDonut.EmitCompact = 0
loJsonDonut.LoadPredefined("donut")
? loJsonDonut.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:
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Hashtable')
loDonutValues = CreateObject('Chilkat.Hashtable')
loDonutValues.AddStr("id","0001")
loDonutValues.AddStr("name","Cake")
loDonutValues.AddStr("imageUrl","images/0001.jpg")
loDonutValues.AddInt("imageWidth",200)
loDonutValues.AddInt("imageHeight",200)
loDonutValues.AddStr("thumbUrl","images/thumbnails/0001.jpg")
loDonutValues.AddInt("thumbWidth",32)
loDonutValues.AddInt("thumbHeight",32)

* Emit with variable substitutions:
lnOmitEmpty = 1
? loJsonDonut.EmitWithSubs(loDonutValues,lnOmitEmpty)

* 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:
loDonutValues.AddStr("id","0002")
loDonutValues.AddStr("imageUrl","images/0002.jpg")
loDonutValues.AddStr("thumbUrl","images/thumbnails/0002.jpg")

? loJsonDonut.EmitWithSubs(loDonutValues,lnOmitEmpty)

* 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
* 	  }
* 	}

RELEASE loJson
RELEASE loJsonTemplate
RELEASE loJsonDonut
RELEASE loDonutValues