JSON Fetch / Null result == no callback

[yavery]

Hi,

With Isomorphic SmartClient 8 GA (JS), I use the following code:

var ds = DataSource.create
({
	dataFormat : 'json',
	dataProtocol : 'postMessage',
	recordXPath : '/Allowance',
	dataURL : encodeURI(myURL),
	fields :
	[
		{ name : 'Buyer.Code', type : 'text' },
		{ name : 'Buyer.Name', type : 'text' }
	]
});

var requestProperties =
{
	httpMethod : 'POST',
	contentType : 'application/json',
	httpHeaders : { 'Accept' : 'application/json' },
	data : myJSONdata,
	useSimpleHttp : true,
	bypassCache : true,
	showPrompt : true
};

ds.fetchData(null,
	function(dsResponse, data, dsRequest)
	{
           // I need this callback to get executed even when data == null
	}, requestProperties);

When my JSON service returns no data, I get the following warning in the ISC console :

08:47:09.471:XRP8:WARN:DataSource:isc_DataSource_1:Evaluating JSON reply resulted in empty value. JSON text:
"null"

And my callback never gets executed.

I quickly looked at the DataSource code and found the following in the _handleJSONTextReply method:

       // warn and bail if server response object evals to null.
       // This can happen if the response is "", or if it's something like "var foo = {};"
       // where the result of the eval is undef.
       // Avoids a JS error in handleJSONReply
       if (jsonObjects == null) {
           this.logWarn("Evaluating JSON reply resulted in empty value. JSON text:\r" 
                        + this.echo(jsonText));
         return;
     }

Is there any way to have the callback executed with data == null as its parameter ?

Thanks again for the assistance,

[Isomorphic]

You do need to send a valid JSON response - it can be just {}, is that an issue?

[yavery]

I use the Jersey/JAXB framework on the server, and somehow when it serialized empty collections, it returns null, instead of [] ...

I'm currently investigating if I can change that behavior on the server without breaking anything else, and I'll let you know if I come up
with something.

If I can't, would it be possible for you guys not to break to function call flow, and have my fetch() callback fired with null ? or some
other alternative ?

In any case, I'll come back to you with more info if I can fix this on the server ...

[yavery]

I've been playing with Jersey/JAXB for a while trying to have it return empty collections as [], but can't make it happen.

How complex/feasible would it be for you guys to have the callback fired with a null when this happens? Or do you have
something else you could propose?

Thanks,

[Isomorphic]

We plan to take a look at it, but unless you fix the serialization behavior you'd still have a warning every time. Better to catch the bad cases in JAXB by looking at the data right before passing to JAXB and doing a direct Servlet response in that case.

[yavery]

We fixed this in our JAXB collection implementation (server) so this is
no longer an issue for us as the returned data is now JSON compliant.

Thanks,