ASP.NET MVC Web API and passing oData query

Question

I'm currently executing Web API with oData filter requests as follows:

public IQueryable<OrganizationViewModel> Get(ODataQueryOptions<Organization> oDataQuery)
{
    var query = new FindOrganizationsQuery(oDataQuery);
    var result =_findOrganizationsQueryHandler.Execute(query);
    return result.Organizations.Select(o => new OrganizationViewModel { Id = o.PublicId, Name = o.Name });
}

The handler looks like:

public FindOrganizationsQueryResult Execute(FindOrganizationsQuery request)
{
    var organizations = request.ODataQuery.ApplyTo(_mgpQueryContext.Organizations).Cast<Organization>();            
    return new FindOrganizationsQueryResult(organizations);
}

And the query class looks like:

public class FindOrganizationsQuery
{
    public FindOrganizationsQuery(ODataQueryOptions<Organization> oDataQuery)
    {
        ODataQuery = oDataQuery;
    }
    public ODataQueryOptions<Organization> ODataQuery { get; set; }
}

So if I pass an oData filter with the request, it is handled nicely and this all works fine.

But now, instead of passing the type ODataQueryOptions to the Get operation, I would like to have the FindOrganizationsQuery class, like:

public IQueryable<OrganizationViewModel> FindOrganizations(FindOrganizationsQuery query)
{
    // query is null
}

However, the query parameters is always null. How can I pass the oData filter if the ODataQueryOptions parameters is in another class?

Answer 1

You can write a custom parameter binding attribute for FindOrganizationsQuery the same way we do for ODataQueryOptions and then attribute your FindOrganizationsQuery with that attribute.

Some sample code below,

public class CustomQueryBindingAttribute : ParameterBindingAttribute
{
    public override HttpParameterBinding GetBinding(HttpParameterDescriptor parameter)
    {
        return new CustomQueryBinding(parameter);
    }

    internal class CustomQueryBinding : HttpParameterBinding
    {
        public CustomQueryBinding(HttpParameterDescriptor parameter)
            : base(parameter)
        {
        }

    internal class CustomQueryBinding : HttpParameterBinding
    {
        public CustomQueryBinding(HttpParameterDescriptor parameter)
            : base(parameter)
        {
        }

        public override Task ExecuteBindingAsync(ModelMetadataProvider metadataProvider,
            HttpActionContext actionContext, CancellationToken cancellationToken)
        {
            IEdmModel model = actionContext.Request.GetEdmModel() ?? actionContext.ActionDescriptor.GetEdmModel(typeof(Organization));
            ODataQueryContext queryContext = new ODataQueryContext(model, typeof(Organization));

            object customQuery = CreateCustomQuery(queryContext, actionContext.Request);
            SetValue(actionContext, customQuery);

            return Task.FromResult(0);
        }

        private object CreateCustomQuery(ODataQueryContext queryContext, HttpRequestMessage request)
        {
            Type parameterType = Descriptor.ParameterType;
            // Assuming all custom queries have this public property.
            Type oDataQueryOptionsOfTType = parameterType.GetProperty("ODataQuery").PropertyType;

            object odataQueryOptions = Activator.CreateInstance(oDataQueryOptionsOfTType, queryContext, request);
            return Activator.CreateInstance(parameterType, odataQueryOptions);
        }
    }
}

and the extension method I copied from web API source code as it is not public.

public static class HttpActionDescriptorExtensions
{
    internal const string EdmModelKey = "MS_EdmModel";

    internal static IEdmModel GetEdmModel(this HttpActionDescriptor actionDescriptor, Type entityClrType)
    {
        // save the EdmModel to the action descriptor
        return actionDescriptor.Properties.GetOrAdd(EdmModelKey + entityClrType.FullName, _ =>
        {
            ODataConventionModelBuilder builder = new ODataConventionModelBuilder(actionDescriptor.Configuration, isQueryCompositionMode: true);
            EntityTypeConfiguration entityTypeConfiguration = builder.AddEntity(entityClrType);
            builder.AddEntitySet(entityClrType.Name, entityTypeConfiguration);
            IEdmModel edmModel = builder.GetEdmModel();
            return edmModel;
        }) as IEdmModel;
    }
}

I have the complete sample here.