The roadmap for serialization formats

We have been talking for a while about a more efficient format for JSON serialization. The new serialization format will be part of the OData v3 protocol, and we believe that the much-improved JSON format should be the default response when requesting application/json.

You may notice that when you upgrade to WCF DS 5.0, requesting the old JSON format is a bit different. To get the old JSON format, you must now explicitly request application/json;odata=verbose or set the MaxDataServiceVersion header to 2.0.

When will I get a 415 response and what can I do about it?

WCF Data Services 5.0 will return a 415 in response to a request for application/json if the service configuration allows a v3 response and if the client does not specify a MaxDataServiceVersion header or specifies a MaxDataServiceVersion header of 3.0. Clients should always send a value for the MaxDataServiceVersion header to ensure forward compatibility.

There are two ways to get a response formatted with JSON verbose:

1. Set the MaxDataServiceVersion header to 2.0 or less. For instance:

GET http://odata.example.org/Items?$top=5 HTTP/1.1

Host: odata.example.org

Connection: keep-alive

User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.152 Safari/535.19

Accept: application/json

Accept-Encoding: gzip,deflate,sdch

Accept-Language: en-US,en;q=0.8

Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3

MaxDataServiceVersion: 2.0

2. Request a content type of application/json;odata=verbose. For instance:

GET http://odata.example.org/Items?$top=5 HTTP/1.1

Host: odata.example.org

Connection: keep-alive

User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.152 Safari/535.19

Accept: application/json;odata=verbose

Accept-Encoding: gzip,deflate,sdch

Accept-Language: en-US,en;q=0.8

Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3

MaxDataServiceVersion: 3.0

It’s possible to modify the headers with jQuery as follows:

$.ajax(url, {

    dataType: "json", // this tells jquery that you are expcting a json object and so it will parse the data for you.

    beforeSend: function (xhr) {

        xhr.setRequestHeader("Accept", "application/json;odata=verbose");

        xhr.setRequestHeader("MaxDataServiceVersion", "3.0");

    },

    success: function (data) {

       // do something interesting with the data you get back.

    }

});

Why did WCF DS 5.0 ship before JSON light?

We had a set of features that were ready to be released as part of WCF DS 5.0. The more efficient JSON implementation is currently in progress and will be released sometime later this year.