EF6.1 Getting Key Properties for an Entity

Today I had a question show up in my inbox about finding the key properties of a given entity type. Searching around I didn’t find a good existing post about this, so here is the code you need. The code provides a couple of simple extension methods to DbContext.

Note that the code is somewhat ugly for a fairly simple task… our team knows that and in EF7 things will be a LOT more straightforward.

using System;
using System.Data.Entity;
using System.Data.Entity.Core.Metadata.Edm;
using System.Data.Entity.Infrastructure;
using System.Linq;

namespace System.Data.Entity
{
    public static class DbContextExtensions
    {
        public static string[] GetKeyNames<TEntity>(this DbContext context)
            where TEntity : class
        {
            return context.GetKeyNames(typeof(TEntity));
        }

        public static string[] GetKeyNames(this DbContext context, Type entityType)
        {
            var metadata = ((IObjectContextAdapter)context).ObjectContext.MetadataWorkspace;

            // Get the mapping between CLR types and metadata OSpace
            var objectItemCollection = ((ObjectItemCollection)metadata.GetItemCollection(DataSpace.OSpace));

            // Get metadata for given CLR type
            var entityMetadata = metadata
                    .GetItems<EntityType>(DataSpace.OSpace)
                    .Single(e => objectItemCollection.GetClrType(e) == entityType);

            return entityMetadata.KeyProperties.Select(p => p.Name).ToArray();
        }
    }
}
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