How can I manually execute Breeze filters in Web Api?

Question

I want to use some external server-side logic to modify properties on the results of a query. To do this, I'll need to apply the Breeze query options, modify the result set, and return it.

I know essentially how I can apply OdataQueryOptions to my query, but I don't want to miss out on all the things that BreezeJS does that Web Api's OData doesn't. For example, I want to keep inlineCount.

How can I do this? Is there some way to hook into Breeze's query modifying code?

In case it matters, I'm using Entity Framework 6 and Web Api 2.

Answer 1

Ok, I'm not sure if there's a better way (because this seems like a lot of work for what seems like it would be a common use case), but here's how I solved this.

I inherited from the QueryHelper class to modify the PostExecuteQuery method to execute a delegate.

public class ExtendedQueryHelper : QueryHelper
{
    public ExtendedQueryHelperOptions Options { get; set; }

    public ExtendedQueryHelper(ODataQuerySettings querySettings) : base(querySettings)
    {}

    public override IEnumerable PostExecuteQuery(IEnumerable queryResult)
    {
        if (Options != null && Options.PostExecuteQueryHandler != null)
        {
            return Options.PostExecuteQueryHandler(queryResult);
        }

        return base.PostExecuteQuery(queryResult);
    }
}

The delegate is defined in a class called ExtendedQueryHelperOptions

public class ExtendedQueryHelperOptions
{
    private const string EXTENDED_QUERY_HELPER_OPTIONS_KEY = "EXTENDED_QUERY_HELPER_OPTIONS_KEY";
    public delegate IEnumerable PostExecuteQueryDelegate(IEnumerable queryResult);

    public PostExecuteQueryDelegate PostExecuteQueryHandler { get; set; }

    public void InjectIntoRequest(HttpRequestMessage request)
    {
        request.Properties.Add(EXTENDED_QUERY_HELPER_OPTIONS_KEY, this);
    }

    public static ExtendedQueryHelperOptions GetFromRequest(HttpRequestMessage request)
    {
        object options;
        request.Properties.TryGetValue(EXTENDED_QUERY_HELPER_OPTIONS_KEY, out options);

        return (ExtendedQueryHelperOptions)options;
    }
}

In order to set these options, I had to inherit from BreezeQueryableAttribute and inject these options when the QueryHelper is being created:

public class ExtendedBreezeQueryableAttribute : BreezeQueryableAttribute
{
    protected HttpRequestMessage Request { get; set; }

    public override void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
    {
        Request = actionContext.Request;
        base.OnActionExecuting(actionContext);
    }

    protected override QueryHelper NewQueryHelper()
    {
        var queryHelper = new ExtendedQueryHelper(GetODataQuerySettings());
        queryHelper.Options = ExtendedQueryHelperOptions.GetFromRequest(Request);

        return queryHelper;
    }
}

Now I can inject code to be run on the filtered results like this:

[BreezeController]
public class BreezeController : BaseController
{
    //...

    [HttpGet]
    [ExtendedBreezeQueryable]
    public IQueryable<Foo> Foos()
    {
        var options = new ExtendedQueryHelperOptions
        {
            PostExecuteQueryHandler = delegate(IEnumerable results) {
                // This code will be run after the querying has been
                // applied by Breeze
                var foos = results.Cast<Foo>().ToList();

                foreach (var foo in foos)
                {
                    foo.ComputedProperty = ComputeSomething();
                }

                return foos;
            }
        };

        // Inject these options into the Request, so the ExtendedBreezeQueryableAttribute
        // can get to them later
        options.InjectIntoRequest(Request);
        return Db.Foos;
    }
}