Make Entity Framework Linq query async

Question

I have a function that populates a combo box in my winform app. The operation takes a few seconds so I'd like to make it async.

Here is the function:

public static List<string> GetAllPostCodeRegions(string country)
{
    using (var db = new PlaceDBContext())
    {
        var regions = db.PostCodes.Where(pc => pc.Country == country).OrderBy(pc => pc.Region).Select(pc => pc.Region).Distinct().ToList();

        return regions;
    }
}

I tried just adding in async keywords like below:

public async static Task<List<string>> GetAllPostCodeRegions(string country)
{
    using (var db = new PlaceDBContext())
    {
        var regions = db.PostCodes.Where(pc => pc.Country == country).OrderBy(pc => pc.Region).Select(pc => pc.Region).Distinct().ToList();

        return regions;
    }
}

But this isn't awaiting anything and the UI still locks when I call:

var regions = await DataFunctions.GetAllPostCodeRegions("UK");

How do I make this operation async and stop UI locking up?

You need to call ToListAsync() instead of ToList() and add an await in front of that statement. This requires Entity Framework 6 or higher. — Jeff Prince
– Jeff Prince, Commented Sep 3, 2015 at 3:35
Thanks. I also needed to add using System.Data.Entity as using the ctrl + period didn't suggest it for some reason. — Guerrilla
– Guerrilla, Commented Sep 3, 2015 at 3:51

bto.rdz · Accepted Answer · 2015-09-03 03:43:13Z

1

you can Try .ToListAsync or:

public static Task<List<string>> GetAllPostCodeRegions(string country)
{
    return Task.Run(() => 
       {
          using (var db = new PlaceDBContext())
          {
               return db.PostCodes
                        .Where(pc => pc.Country == country)
                        .OrderBy(pc => pc.Region)
                        .Select(pc => pc.Region).Distinct().ToList();
          }
      });        
}

answered Sep 3, 2015 at 3:43

bto.rdz

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1 Comment

bto.rdz Over a year ago

I said both options, make it by your self is not that hard

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