IQueryable does not contain definition for GetAwaiter

Question

I'm using WebAPI in entity framework to create a new endpoint and I am having some issues. I'm trying to use a Linq Where statement to get my data, but I'm receiving the following error.

'IQueryable' does not contain a definition for 'GetAwaiter' and no extension method 'GetAwaiter' accepting a first argument of type 'IQueryable' could be found (are you missing a using directive or an assembly reference?)

Here is my code.

    [ResponseType(typeof(Vocab))]
    public async Task<IHttpActionResult> GetVocabByLesson(int lessonId)
    {
        Vocab vocab = await db.Vocabs.Where(a => a.LessonId == lessonId);
        if (vocab == null)
            return NotFound();

        return Ok(vocab);
    }

Well, why did you expect that to be okay? How do you expect the result of Where to be awaitable? And when do you ever expect the result to be null? (Where returns a sequence - which may be empty, but which is never null...) — Jon Skeet

octavioccl octavioccl · Accepted Answer · 2016-12-05T15:54:11

Use FirstOrDefaultAsync extension method:

[ResponseType(typeof(Vocab))]
public async Task<IHttpActionResult> GetVocabByLesson(int lessonId)
{
        Vocab vocab = await db.Vocabs.FirstOrDefaultAsync(a => a.LessonId == lessonId);
        if (vocab == null)
            return NotFound();

        return Ok(vocab);
}

By your code I can deduct you want to return just an element, that's why I have suggested to use FirstOrDefaultAsync. But in case you want to get more than one element that meets some condition then use ToListAsync:

[ResponseType(typeof(Vocab))]
public async Task<IHttpActionResult> GetVocabByLesson(int lessonId)
{
        var result= await db.Vocabs.Where(a => a.LessonId == lessonId).ToListAsync();
        if (!result.Any())
            return NotFound();

        return Ok(result);
}

IQueryable does not contain definition for GetAwaiter

1 Answers