OData web api - upgrade to AsyncEntitySetController - Get method

Question

We have WEB API which uses OData. Our controllers inherit from EntitySetController and now we are changing it to AsyncEntitySetController

Patch, Post, Put, Get(key) methods are easy to change, but the problem is with Get method.

In EntitySetController it returns IQueryable, filters specified in URI are further applied and then query is executed.

But in AsyncEntitySetController it returns IEnumerable so we need to call ToListAsync in method and I am affraid that parameters from URI are not applied or query is called before the filters are applied and filters are applied to memory collection.

How to achieve that it behaves the same way as with EntitySetController, so:

iqueryable is made
filters from URI are applied
query is called in async/await way?

@NahuelPrieto: looks like I did. I need to prove it in real (unfortunately, I am too busy to get back to it), but it seems that using QueryOptions.ApplyTo(query) where 'query' is your IQueryable you need to get results from and 'QueryOptions' are present on controller instance will apply query parameters from URI. That was crucial part, rest should be smooth. — michal.jakubeczy

michal.jakubeczy michal.jakubeczy · Accepted Answer · 2018-07-17T05:54:35

I managed to solve it by using QueryOptions.ApplyTo(query). So my previous code in controller class derived from EntitySetController:

public override IQueryable<Entity> Get()
{
    return this.DataContext.Entities;
}

was transformed into controller class derived from AsyncEntitySetController, like this:

public override Task<IEnumerable<Entity>> Get()
{
    var query = this.DataContext.Entities;

    query = (IQueryable<Entity>)this.QueryOptions.ApplyTo(query);
    return query.ToListAsync();
}

One note to mention. Skip from query parameters in URI gets applied twice, see: WebAPI OData $Skip on custom IQueryable double applied

You can implement your own EnableQuery attribute like this and decorate Get method with that in controller:

public sealed class EnableQueryIgnoreSkipAttribute : EnableQueryAttribute
{
    public override IQueryable ApplyQuery(IQueryable queryable, ODataQueryOptions queryOptions)
    {
        // Do not apply Skip
        var skipOption = new SkipQueryOption("0", queryOptions.Context);
        typeof(ODataQueryOptions).GetProperty(nameof(ODataQueryOptions.Skip)).SetValue(queryOptions, skipOption, null);

        return base.ApplyQuery(queryable, queryOptions);
    }
}

And decorate method like this:

[EnableQueryIgnoreSkip]
public override Task<IEnumerable<Entity>> Get()

OData web api - upgrade to AsyncEntitySetController - Get method

1 Answers