entity-framework-4 - Linq 中的 DateTime 操作到实体查询

Question

运行此代码:

public bool CheckTime(DateTime date, int UserID, int TotalTimeMin)
        {
            using (var context = new myDB())
            {         
                var assginments = from c in context.Assignments.Where(x=>(x.AssignmentDateTime < date && x.AssignmentDateTime.Value.AddMinutes(TotalTimeMin) > date) || 
                    (x.AssignmentDateTime < date.AddMinutes(TotalTimeMin))) select c;

                if(assginments != null) return false;
                else return true;
            }


        }

我收到这个错误。

LINQ to Entities does not recognize the method 'System.DateTime AddMinutes(Double)' method, and this method cannot be translated into a store expression.

TotalTimeMin 是整数。我不确定是什么原因造成的:
AssignmentDateTime 是 DateTime？也许这就是问题所在？

Answer 1

使用 EntityFunctions.AddMinutes (需要 EF 4):

    public bool CheckTime(DateTime date, int UserID, int TotalTimeMin)
    {
        using (var context = new myDB())
        {         
            var assginments = context.Assignments
                                     .Where(x=>(x.AssignmentDateTime < date 
                                                && EntityFunctions.AddMinutes(x.AssignmentDateTime,TotalTimeMin) > date) 
                                                || (x.AssignmentDateTime < date.AddMinutes(TotalTimeMin)));

            if(assginments != null) return false;
            else return true;
        }
    }

请注意 assignments永远不会为空(但它可能为空——测试 assignments.Any())。