JSON.NET as a WebAPI 2 OData serializer vs ODataMediaTypeFormatter

Question

I\'m trying to use JSON.NET as a default serializer in WebAPI 2 stack. I\'ve implemented JsonMediaTypeFormatter, in which I\'ve used JSON.NET serializer for serialize/deseri

Answer 1

If it helps anyone else, here is how I re-used my Json.NET custom serializer in OData.

In Startup, insert your custom serializer provider:

    var odataFormatters = ODataMediaTypeFormatters.Create(new MyODataSerializerProvider(), new DefaultODataDeserializerProvider());
    config.Formatters.InsertRange(0, odataFormatters);

Here is my MyODataSerializerProvider.cs:

    public class MyODataSerializerProvider : DefaultODataSerializerProvider
    {
        public override ODataEdmTypeSerializer GetEdmTypeSerializer(IEdmTypeReference edmType)
        {
            switch (edmType.TypeKind())
            {
                case EdmTypeKind.Enum:
                    ODataEdmTypeSerializer enumSerializer = base.GetEdmTypeSerializer(edmType);
                    return enumSerializer;

                case EdmTypeKind.Primitive:
                    ODataEdmTypeSerializer primitiveSerializer = base.GetEdmTypeSerializer(edmType);
                    return primitiveSerializer;

                case EdmTypeKind.Collection:
                    IEdmCollectionTypeReference collectionType = edmType.AsCollection();
                    if (collectionType.ElementType().IsEntity())
                    {
                        ODataEdmTypeSerializer feedSerializer = base.GetEdmTypeSerializer(edmType);
                        return feedSerializer;
                    }
                    else
                    {
                        ODataEdmTypeSerializer collectionSerializer = base.GetEdmTypeSerializer(edmType);
                        return collectionSerializer;
                    }

                case EdmTypeKind.Complex:
                    ODataEdmTypeSerializer complexTypeSerializer = base.GetEdmTypeSerializer(edmType);
                    return complexTypeSerializer;

                case EdmTypeKind.Entity:
                    ODataEdmTypeSerializer entityTypeSerializer = new MyODataEntityTypeSerializer(this);
                    return entityTypeSerializer;                    

                default:
                    return null;
            }
        }
    }

This then calls into MyODataEntityTypeSerializer.cs:

public class MyODataEntityTypeSerializer : ODataEntityTypeSerializer
{
    private static Logger logger = LogManager.GetCurrentClassLogger();

    public DocsODataEntityTypeSerializer(ODataSerializerProvider serializerProvider)
        : base(serializerProvider)
    {
    }

    public override ODataEntry CreateEntry(SelectExpandNode selectExpandNode, EntityInstanceContext entityInstanceContext)
    {
        ODataEntry entry = base.CreateEntry(selectExpandNode, entityInstanceContext);
        if(entry.TypeName == typeof(YourObject).FullName)
        {
            YourObjectEntryConverter converter = new YourObjectEntryConverter(entry);
            entry = converter.Convert();
        }
        return entry;
    }
}

Note that YourObject is your custom class that has a Json.NET serializer attached, via attribute or config.

Here's the converter class:

public class YourObjectEntryConverter
{
    private ODataEntry _entry;
    private string[] _suppressed_properties = {
                                                "YourProperty1", "YourProperty2"
                                              };

    public YourObjectEntryConverter(ODataEntry entry)
    {
        _entry = entry;
    }

    public ODataEntry Convert()
    {
        // 1st pass: create a poco from odata
        YourObject yours = new YourObject();
        PropertyInfo[] properties = typeof(YourObject).GetProperties();           
        foreach (PropertyInfo property in properties)
        {
            foreach (ODataProperty odata_property in _entry.Properties)
            {
                if (property.Name == odata_property.Name)
                {
                    if (odata_property.Value is ODataCollectionValue)
                    {
                        // my json de/serialization populates these; ymmv
                    }
                    else if (odata_property.Value is DateTimeOffset)
                    {
                        DateTimeOffset? dto = odata_property.Value as DateTimeOffset?;
                        property.SetValue(yours, dto.Value.DateTime);
                    }
                    else if (odata_property.Value == null)
                    {
                        property.SetValue(yours, odata_property.Value);
                    }
                    else if (ODataUtils.IsPrimitiveType(odata_property.Value.GetType()))
                    {
                        property.SetValue(yours, odata_property.Value);
                    }
                    // todo complex types
                    break;
                }
            }
        }

        // 2nd pass: use json serializer in the business layer to add markup
        // this call fires the "decorators" in YourObjectSerializer.cs via Json.NET
        string json = JsonConvert.SerializeObject(yours);
        // suck the newly added info back in
        YourObject serialized = JsonConvert.DeserializeObject(json);

        // 3rd pass: scrape the json poco and shovel it back into odata
        foreach (PropertyInfo property in properties)
        {
            foreach (ODataProperty odata_property in _entry.Properties)
            {
                if (property.Name == odata_property.Name)
                {
                    if (odata_property.Value is ODataCollectionValue)
                    {
                        var collection = odata_property.Value as ODataCollectionValue;
                        var collection_typename = property.PropertyType.ToString();
                        if (collection_typename.Contains("List") && collection_typename.Contains("YourSubObject"))
                        {
                            IList subobjects = property.GetValue(serialized) as IList;
                            List subobjects_list = new List();
                            foreach(YourSubObject subobject in subobjects)
                            {
                                subobjects_list.Add(ODataUtils.CreateComplexValue(typeof(YourSubObject), subobject));
                            }
                            collection.Items = subobjects_list.AsEnumerable();
                        }
                    }
                    else if (odata_property.Value is DateTimeOffset)
                    {
                        DateTimeOffset? dto = odata_property.Value as DateTimeOffset?;
                        property.SetValue(yours, dto.Value.DateTime);
                    }
                    else
                    {
                        object new_value = property.GetValue(serialized);
                        object old_value = property.GetValue(yours);
                        if (null == old_value && null != new_value)
                        {
                            Type t = new_value.GetType();
                            if (!ODataUtils.IsPrimitiveType(t))
                            {
                                odata_property.Value = ODataUtils.CreateComplexValue(t, new_value);
                            }
                            else
                            {
                                odata_property.Value = new_value;
                            }                                
                        }
                        else if (odata_property.Value is Guid)
                        {
                            Guid? new_guid = new_value as Guid?;
                            Guid? old_guid = old_value as Guid?;
                            if (Guid.Empty == old_guid.Value && Guid.Empty != new_guid.Value)
                            {
                                odata_property.Value = new_value;
                            }
                        }
                    }
                    break;
                }
            }
        }

        // 4th pass: add stuff that json added to the entry
        List new_properties = new List();
        foreach (PropertyInfo property in properties)
        {
            object value = property.GetValue(serialized);
            if (null != value)
            {
                bool lost_property = true; // couldn't resist
                foreach (ODataProperty odata_property in _entry.Properties)
                {
                    if (property.Name == odata_property.Name)
                    {
                        lost_property = false;
                        break;
                    }
                }
                if (lost_property)
                {
                    ODataProperty new_property = ODataUtils.CreateProperty(property.Name, value);
                    new_properties.Add(new_property);
                }
            }
        }


        // 5th pass: strip odata properties we don't want to expose externally
        List unsuppressed_properties = new List();
        foreach (ODataProperty odata_property in _entry.Properties)
        {
            if (!_suppressed_properties.Contains(odata_property.Name))
            {
                unsuppressed_properties.Add(odata_property);
            }
        }
        unsuppressed_properties.AddRange(new_properties); // from 4th pass
        _entry.Properties = unsuppressed_properties.AsEnumerable();

        return _entry;

    }
}

Lastly, here's my utils class:

public class ODataUtils
{
    public static bool IsPrimitiveType(Type t)
    {
        if (!t.IsPrimitive && t != typeof(Decimal) && t != typeof(String) && t != typeof(Guid) && t != typeof(DateTime)) // todo
        {
            return false;
        }
        return true;
    }

    public static ODataProperty CreateProperty(string name, object value)
    {
        object property_value = value;
        if(value != null)
        {
            Type t = value.GetType();
            if (!IsPrimitiveType(t))
            {
                property_value = CreateComplexValue(t, value);
            }
            else if (t == typeof(DateTime) || t == typeof(DateTime?))
            {
                DateTime dt = (DateTime)value;
                dt = DateTime.SpecifyKind(dt, DateTimeKind.Utc);
                DateTimeOffset dto = dt;
                property_value = dto;
            }
        }
        ODataProperty new_property = new ODataProperty()
        {
            Name = name,
            Value = property_value
        };
        return new_property;
}

    public static ODataComplexValue CreateComplexValue(Type type, object value)
    {
        ODataComplexValue complex_value = new ODataComplexValue();
        complex_value.TypeName = type.ToString();
        PropertyInfo[] complex_properties = type.GetProperties();
        List child_properties = new List();
        foreach (PropertyInfo property in complex_properties)
        {
            ODataProperty child_property = CreateProperty(property.Name, property.GetValue(value));
            child_properties.Add(child_property);
        }
        complex_value.Properties = child_properties.AsEnumerable();
        return complex_value;
    }
}

Its all a horrible hack, but if you have a bunch of special Json.NET serialization code for your objects that you want to re-use in OData, this worked for me.