How to query Code First entities based on rowversion/timestamp value?

Question

I\'ve run into a case where something that worked fairly well with LINQ to SQL seems to be very obtuse (or maybe impossible) with the Entity Framework. Specifically, I\'ve g

Answer 1

Here is yet another workaround available to EF 6.x that doesn't require creating functions in the database but uses model defined functions instead.

Function definitions (this goes inside the section in your CSDL file, or inside section if you are using EDMX files):

  
  
  source < target


  
  
  source <= target


  
  
  source > target


  
  
  source >= target

Note that I haven't written the code to create the functions using the APIs available in Code First, but similar to code to what Drew proposed or the model conventions I wrote some time ago for UDFs https://github.com/divega/UdfCodeFirstSample, should work

Method definition (this goes in your C# source code):

using System.Collections;
using System.Data.Objects.DataClasses;

namespace TimestampComparers
{
    public static class TimestampComparers
    {

        [EdmFunction("TimestampComparers", "IsLessThan")]
        public static bool IsLessThan(this byte[] source, byte[] target)
        {
            return StructuralComparisons.StructuralComparer.Compare(source, target) == -1;
        }

        [EdmFunction("TimestampComparers", "IsGreaterThan")]
        public static bool IsGreaterThan(this byte[] source, byte[] target)
        {
            return StructuralComparisons.StructuralComparer.Compare(source, target) == 1;
        }

        [EdmFunction("TimestampComparers", "IsLessThanOrEqualTo")]
        public static bool IsLessThanOrEqualTo(this byte[] source, byte[] target)
        {
            return StructuralComparisons.StructuralComparer.Compare(source, target) < 1;
        }

        [EdmFunction("TimestampComparers", "IsGreaterThanOrEqualTo")]
        public static bool IsGreaterThanOrEqualTo(this byte[] source, byte[] target)
        {
            return StructuralComparisons.StructuralComparer.Compare(source, target) > -1;
        }
    }
}

Note also that I have defined the methods as extension methods over byte[], although this is not necessary. I also provided implementations for the methods so that they work if you evaluate them outside queries, but you can choose as well to throw NotImplementedException. When you use these methods in LINQ to Entities queries, we will never really invoke them. Also not that I have made the first argument for EdmFunctionAttribute “TimestampComparers”. This has to match the namespace specified in the section of your conceptual model.

Usage:

using System.Linq;

namespace TimestampComparers
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var context = new OrdersContext())
            {
                var stamp = new byte[] { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, };

                var lt = context.OrderLines.FirstOrDefault(l => l.TimeStamp.IsLessThan(stamp));
                var lte = context.OrderLines.FirstOrDefault(l => l.TimeStamp.IsLessThanOrEqualTo(stamp));
                var gt = context.OrderLines.FirstOrDefault(l => l.TimeStamp.IsGreaterThan(stamp));
                var gte = context.OrderLines.FirstOrDefault(l => l.TimeStamp.IsGreaterThanOrEqualTo(stamp));

            }
        }
    }
}