How to Convert DataReader Result to Entity? ->use Emit

Now I want to Convert a DataReader to an Entity . I have a method like this:

 private static void ReadInt32(ILGenerator il, LocalBuilder item,
                List<DbColumnInfo> columnInfoes, LocalBuilder[] colIndices, int i)
            {
               il.Emit(OpCodes.Ldloc_S, item);
                il.Emit(OpCodes.Ldarg_0);
                il.Emit(OpCodes.Ldloc_S, colIndices[i]);

                il.Emit(OpCodes.Callvirt, DataRecord_GetInt32);
                il.Emit(OpCodes.Callvirt, columnInfoes[i].SetMethod);

}

and call the method like here,

 if (IsCompatibleType(columnInfoes[i].Type, typeof(int)))
                    {
                        // item.%Propert开发者_Go百科y% = arg.GetInt32(%index%);
                        ReadInt32(il, item, columnInfoes, colIndices, i);
                    }

unfortunately, there will come up an Exception if the Data Filed in DB is NULL. As int type can't be NULL value but I made it transfer to int?. then turns out that my calling method works well.

but here I want an extension that is while Data Filed in DB is NULL, we can use Custom attribute to indicate a default value. So I re-defined ReadInt32 as following, But to my surprise, there always comming up JIT inner Exception. I'm not familiar with IL, I really looking forward some help for you all, really appreciate.

change the code's as following,but still exist error,the exception type is : System.EntryPointNotFoundException:

 var local = il.DeclareLocal(columnInfoes[i].Type);//int i
            Label intNull = il.DefineLabel();//int intNull;
            Label intCommon = il.DefineLabel();


            il.Emit(OpCodes.Ldloca, local);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldloc_S, colIndices[i]);
            il.Emit(OpCodes.Callvirt, DataRecord_IsDBNull);// int i=isdbnull?
            il.Emit(OpCodes.Brtrue_S, intNull);// int i=isdbnull?intNull

            il.Emit(OpCodes.Ldloc_0);
            il.Emit(OpCodes.Ldloc_S, colIndices[i]);//int i=isdbnull?1000:getInt(32)

            il.Emit(OpCodes.Callvirt, DataRecord_GetInt32);//int i=isdbnull?1000:getInt32(i);
            il.Emit(OpCodes.Br_S, intCommon);

            il.MarkLabel(intNull);;
            il.Emit(OpCodes.Ldc_I4, 123);//intNull=DefaultValue  columnInfoes[i].DefaultValue
            il.MarkLabel(intCommon);
            il.Emit(OpCodes.Stloc_S, item);
            //il.Emit(OpCodes.Ldloc_S, item);
            il.Emit(OpCodes.Ldloc, local);
            il.Emit(OpCodes.Callvirt, columnInfoes[i].SetMethod);

Just use Dapper. If it's good for SO, it will be good for you, too ;-)