Support change tracking of non-primitive types

ChangeTracker does not detect changes to properties of type Dictionary<,>. In provider for PostgreSQL database database column type hstore is mapped to .net type Dictionary<string,string> but this feature can not be used properly if we do not have change tracking for those properties. One solution would be to use ImmutableDictionary but we want to avoid that.

Steps to reproduce

public class HStoreContext : DbContext
{
   public DbSet<SomeEntity> SomeEntities { get; set; }
}

public class SomeEntity
{
   public int Id { get; set; }
   public Dictionary<string, string> Tags { get; set; }
}

using (HStoreContext ctx = CreateContext())
{
   var entity = new SomeEntity()
   {
       Tags = new Dictionary<string, string>()
   };
   ctx.SomeEntities.Add(entity);
   var num = ctx.SaveChanges();

   Assert.Equal(1, num);

   var entry = ctx.Entry(entity);
   Assert.Equal(EntityState.Unchanged, entry.State);

   entity.Tags.Add("kind", "new");
   ctx.ChangeTracker.DetectChanges();

   Assert.Equal(EntityState.Modified, entry.State); // This fails
}

Further technical details

EF Core version: 2.0.0 Database Provider: Microsoft.EntityFrameworkCore.PostgreSQL Operating system: IDE: Visual Studio 2017

[roji]

Just to report that I’ve value comparison for hstore seems to work perfectly… I’ll be adding comparers to array and other relevant types for 2.1 as well.

Thanks!

[roji]

@ajcvickers if you’re interesting in seeing a complex/interesting comparer implementation, take a look at the array comparer, it will also illustrate some of the issues detailed in #11072.