How to Ignore Null values while serializing OData response

Question

I\'ve a requirement to omit the null valued fields from the response altogether. I can do this by modifying the JsonFormatter Serialization Setting for a normal webapi respo

Answer 1

I know it does not look anyway logical, but simply adding DefaultODataSerializerProvider and DefaultODataDeserializerProvider to the list of Formatters did the trick for me:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        //... 

        var odataFormatters = System.Web.OData.Formatter.ODataMediaTypeFormatters.Create(
            System.Web.OData.Formatter.Serialization.DefaultODataSerializerProvider.Instance, 
            System.Web.OData.Formatter.Deserialization.DefaultODataDeserializerProvider.Instance);
        config.Formatters.AddRange(odataFormatters);

UPDATE

Since the global formatters modification didn't work correctly for me, I chose a different way. First I stepped away from the ODataController and inherited my controller from ApiController using a custom ODataFormatting attribute:

[ODataRouting]
[CustomODataFormatting]
public class MyController : ApiController
{
    ...
}

public class CustomODataFormattingAttribute : ODataFormattingAttribute
{
    public override IList CreateODataFormatters()
    {
        return System.Web.OData.Formatter.ODataMediaTypeFormatters.Create(
            new CustomODataSerializerProvider(),
            new System.Web.OData.Formatter.Deserialization.DefaultODataDeserializerProvider());
    }
}

The formatting attribute replaces the DefaultODataSerializerProvider with a modified one:

public class CustomODataSerializerProvider : DefaultODataSerializerProvider
{
    public override ODataEdmTypeSerializer GetEdmTypeSerializer(IEdmTypeReference edmType)
    {
        if(edmType.Definition.TypeKind == EdmTypeKind.Entity)
            return new CustomODataEntityTypeSerializer(this);
        else 
            return base.GetEdmTypeSerializer(edmType);
    }
}

And the last, the custom serializer filters structural properties with null values:

public class CustomODataEntityTypeSerializer : System.Web.OData.Formatter.Serialization.ODataEntityTypeSerializer
{
    public CustomODataEntityTypeSerializer(ODataSerializerProvider provider)
        : base(provider) { }

    public override ODataProperty CreateStructuralProperty(IEdmStructuralProperty structuralProperty, EntityInstanceContext entityInstanceContext)
    {
        var property = base.CreateStructuralProperty(structuralProperty, entityInstanceContext);
        return property.Value != null ? property : null;
    }
}

This doesn't seem to me like the best possible solution, but this is the one I found.