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I'm trying to use a calculated value in my OrderBy clause in a LINQ query.

The error I am getting is:

DbArithmeticExpression arguments must have a numeric common type.

My model looks like this:

   public class PostModel
    {
        public int ID { get; set; }

        public DateTime Created { get; set; }
        public string Title { get; set; }
        public string Description { get; set; }
        public string FilePath { get; set; }
        public float Rank { get; set; }
        public UserProfile Creator { get; set; }

        public bool ShowPost { get; set; }

        public PostModel()
        {
            Created = DateTime.Now;
            Rank = 0;
            ShowPost = false;
        }
    }

and I'm trying to select posts using this:

 var todaysDate = DateTime.Now.AddDays(-10);
 var result = _database.Posts
    .Where(p => p.ShowPost == true)
    .OrderBy(x => ((float)x.Rank) - (((float)(x.Created - todaysDate).TotalDays)) / 2f)
    .Skip(page * StaticVariables.ResponseDataPageSize)
    .Take(StaticVariables.ResponseDataPageSize)
    .Select(s => new
        {
            id = s.ID,
            rank = s.Rank,
            title = s.Title,
            description = s.Description
        }
    );

It's the order by causing the error. I first thought it was that I was not casting all my variables to the same type, but adding (float) does not seem to help.

The purpose of the code is to make make high ranking posts fall down the list over time as to allow newer information to be shown.

Any ideas?

JensB
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1 Answers1

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Use EntityFunctions in LinqToEntity:

EntityFunctions.DiffDays(todaysDate, x.Created)
Reza ArabQaeni
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  • This works. Thank you. Is this a general limitation to all of LINQ, no "normal" calculations in the requests? – JensB Feb 02 '14 at 11:18