使用反射.FirstOrDefault（谓语）;如何调用IDBSet< T>？

给予IDbSet哪里人包含一个id属性，我怎么能一般执行以下命令：

given an IDbSet where Person contains an "Id" property, how can I execute the following command generically:

var p = PersonDbSet.FirstOrDefault(i=>i.Id = 3);

我可以建立谓词，并获得了FirstOrDefault扩展方法的引用，但我可以'不像是会放在一起：

I can build up the predicate, and get a reference to the FirstOrDefault extension method, but I can't seem to put it all together:

首先谓词

ParameterExpression parameter = Expression.Parameter(entityType, "Id");
MemberExpression property = Expression.Property(parameter, 3);
ConstantExpression rightSide = Expression.Constant(refId);
BinaryExpression operation = Expression.Equal(property, rightSide);
Type delegateType = typeof (Func<,>).MakeGenericType(entityType, typeof (bool));
LambdaExpression predicate  = Expression.Lambda(delegateType, operation, parameter);

现在的扩展方法的引用：

Now a reference to the extension method:

    var method = typeof (System.Linq.Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public)
                .FirstOrDefault(m => m.Name == "FirstOrDefault" && m.GetParameters().Count() == 2);

   MethodInfo genericMethod = method.MakeGenericMethod(new[] { entityType });            

最后尝试执行方法：

Finally try to execute the method:

object retVal = genericMethod.Invoke(null, new object[] {dbSet, predicate});

抛出此消息一个ArgumentException：

throws an ArgumentException with this message:

型'System.Reflection.RuntimePropertyInfo'的对象不能转换为类型'System.Linq.IQuerable`1 [人]'。

"Object of type 'System.Reflection.RuntimePropertyInfo' cannot be converted to type 'System.Linq.IQuerable`1[Person]'."

有什么想法？