我有以下通用扩展方法:
public static T GetById<T>(this IQueryable<T> collection, Guid id)
where T : IEntity
{
Expression<Func<T, bool>> predicate = e => e.Id == id;
T entity;
// Allow reporting more descriptive error messages.
try
{
entity = collection.SingleOrDefault(predicate);
}
catch (Exception ex)
{
throw new InvalidOperationException(string.Format(
"There was an error retrieving an {0} with id {1}. {2}",
typeof(T).Name, id, ex.Message), ex);
}
if (entity == null)
{
throw new KeyNotFoundException(string.Format(
"{0} with id {1} was not found.",
typeof(T).Name, id));
}
return entity;
}
很遗憾,Entity Framework 不知道如何处理这个 predicate
,因为 C# 将该 predicate 转换为以下代码:
e => ((IEntity)e).Id == id
Entity Framework抛出以下异常:
无法将类型'IEntity'强制转换为类型'SomeEntity'。LINQ to Entities仅支持将EDM原始类型或枚举类型进行转换。
我们如何使Entity Framework与我们的IEntity
接口配合工作?