using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Metadata.Edm;
using System.Data.Objects;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication11
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var ctx = new DB1Entities())
            {
                var objt1 = ctx.GetById<T1>(new { ID = 1 });
                var objt2 = ctx.GetById<T2>(new { ID1 = "HDS QQ 1", ID2 = "VSQ 5 GF" });

                var res3 = ctx.TryGetById<T1>(new { ID = 1 }, out objt1);
                var res4 = ctx.TryGetById<T2>(new { ID1 = "HDS QQ 1", ID2 = "VSQ 5 GF" }, out objt2);
            }
        }
    }

    public static class EfHelper
    {
        public static T GetById<T>(this DbContext ctx, object idValue)
        {
            var objCtx = ((IObjectContextAdapter)ctx).ObjectContext;

            var entityKey = CreateEntityKey<T>(objCtx, idValue);

            return (T)objCtx.GetObjectByKey(entityKey);
        }

        public static bool TryGetById<T>(this DbContext ctx, object idValue, out T entity)
        {
            var objCtx = ((IObjectContextAdapter)ctx).ObjectContext;

            var entityKey = CreateEntityKey<T>(objCtx, idValue);

            object tempObj;
            var res = objCtx.TryGetObjectByKey(entityKey, out tempObj);

            entity = (T)tempObj;

            return res;
        }
        
        private static EntityKey CreateEntityKey<T>(ObjectContext ctx, object idValue)
        {
            var entityContainer = ctx.MetadataWorkspace.GetEntityContainer(
                ctx.DefaultContainerName, DataSpace.CSpace);

            var osType = ctx.MetadataWorkspace.GetItem<EntityType>(
                typeof(T).FullName, DataSpace.OSpace);

            var csType = (EntityType)ctx.MetadataWorkspace.GetEdmSpaceType(osType);

            while (csType.BaseType != null)
                csType = (EntityType)csType.BaseType;

            var entitySet = entityContainer.GetEntitySetByName(csType.Name, true);

            var idValueType = idValue.GetType();
            var keyValues = new List<KeyValuePair<string, object>>();
            foreach (var key in csType.KeyMembers)
            {
                var value = idValueType.GetProperty(key.Name).GetValue(idValue);

                keyValues.Add(new KeyValuePair<string, object>(key.Name, value));
            }

            var fullEsName = string.Format("{0}.{1}", entityContainer.Name, entitySet.Name);

            return new EntityKey(fullEsName, keyValues);
        }
    }
}