How to provide custom mediatype formats for OData Api - asp.net-web-api

Question

I am developing an ASP.NET application that uses ODataApiController. The application shows users a grid by querying data and showing it in a table. I would like the ability to export to a number of different formats, including CSV and a custom XML format. Ideally, I would just take the same OData query the grid uses, set the Accepts header, and get back CSV or XML.
I've created MediaTypeFormatters to do what I need, but they only work with "regular" ApiController, not ODataApiController. Looking at the code in github, I see that OData has it's own MediaTypeFormatter scheme to handle various cases, and built in XML and JSON formatters. But I can't see how to hook into this to provide custom formats. I've attempted inheriting ODataMediaTypeFormatter, but a breakpoint set on it never hits.
I am only really interested in output formats here. How can I extend OdataApi to output different formats?

Answer 1

You can use MediaTypeFormatter on OData queries as well. Just add a new class to your project that inherit MediaTypeFormatter. Then add this to your WebApiConfig file on Register:
config.Formatters.Add(new JSONPFormatter(new QueryStringMapping("$format","jsonp","application/javascript")));
If you then query your entity with the $format=jsonp it will return the entity as JSONP. You can also request it with the contenttype application/javascript to get a JSONP return.
Here is a full example for a MediaFormatter for JSONP return. You could easily change it for your need:
using MyProject.Models;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Http.Formatting;
using System.Net.Http.Headers;
using System.ServiceModel.Syndication;
using System.Threading.Tasks;
using System.Web;
using System.Xml;
using Newtonsoft.Json;
namespace SMSIdent.Modules.Formatter
{
/// <summary>
/// Adds a $format=jsop to all odata query
/// </summary>
public class JSONPFormatter : MediaTypeFormatter
{
private readonly string jsMIME = "application/javascript";
public JSONPFormatter()
{
SupportedMediaTypes.Add(new MediaTypeHeaderValue(jsMIME));
}
public JSONPFormatter(MediaTypeMapping mediaTypeMapping) : this()
{
MediaTypeMappings.Add(mediaTypeMapping);
}
//THis checks if you can POST or PUT to this media-formater
public override bool CanReadType(Type type)
{
return false;
}
//this checks if you can GET this media. You can exclude or include your Resources by checking for their types
public override bool CanWriteType(Type type)
{
return true;
}
//This actually takes the data and writes it to the response
public override Task WriteToStreamAsync(Type type, object value, Stream writeStream, System.Net.Http.HttpContent content, System.Net.TransportContext transportContext)
{
//you can cast your entity
//MyType entity=(MyType) value;
var callback=HttpContext.Current.Request.Params["callback"];
return Task.Factory.StartNew(() =>
{
using (StreamWriter sw = new StreamWriter(writeStream))
{
if (string.IsNullOrEmpty(callback))
{
callback = "values";
}
sw.Write(callback + "(" + JsonConvert.SerializeObject(value, Newtonsoft.Json.Formatting.None,
new JsonSerializerSettings
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore
}) + ")");
}
});
}
}
}
Note: I'am using Web API 2. I don't know exactly if it also works in Web Api 1.