#ASP.NET Web API Partial Response Partial Response provides partial response (a.k.a. fields) support for ASP.NET Web API.

##Usage of partial response Register the PartialJsonMediaTypeFormatter in Application_Start (in Global.asax):

GlobalConfiguration.Configuration.Formatters.Clear();
GlobalConfiguration.Configuration.Formatters.Add(new PartialJsonMediaTypeFormatter() { IgnoreCase = true });

Now partial response will be applied to all responses with HTTP status code 200. To force enable/disable partial response for the current response, call the following extension method (in System.Net.Http) on the request:

Request.SetBypassPartialResponse(true|false);

##Understanding the fields parameter

The fields parameter filters the API response so that the response only includes a specific set of fields. The fields parameter lets you remove nested properties from an API response and thereby reduce your bandwidth usage.

The following rules explain the supported syntax for the fields parameter value, which is loosely based on XPath syntax:

• Use a comma-separated list (fields=a,b) to select multiple fields.
• Use an asterisk (fields=*) as a wildcard to identify all fields.
• Use parentheses (fields=a(b,c)) to specify a group of nested properties that will be included in the API response.
• Use a forward slash (fields=a/b) to identify a nested property.

In practice, these rules often allow several different fields parameter values to retrieve the same API response. For example, if you want to retrieve the playlist item ID, title, and position for every item in a playlist, you could use any of the following values:

• fields=items/id,playlistItems/snippet/title,playlistItems/snippet/position
• fields=items(id,snippet/title,snippet/position)
• fields=items(id,snippet(title,position))

Note: As with all query parameter values, the fields parameter value must be URL encoded. For better readability, the examples in this document omit the encoding.

Note: Due to the relatively slow performance of LINQ to JSON (Json.NET), the usage of PartialJsonMediaTypeFormatter has a performance impact compared to the regular Json.NET serializer. Because of the reduced traffic, the overhead in time could be neglected.