c# – 使用linq-to-entities将字符串转换为datetime的一个大问题
发布时间:2020-12-16 01:21:40 所属栏目:百科 来源:网络整理
导读:如何使用 linq将字符串转换为日期时间到实体…. 我有以下查询,其中visit_date列数据类型是字符串… var memberl = from v in abc.visits join m in abc.members on v.member_Id equals m.member_Id where Convert.ToDateTime(v.visit_Date) = startdate Conv
如何使用
linq将字符串转换为日期时间到实体….
我有以下查询,其中visit_date列数据类型是字符串… var memberl = from v in abc.visits join m in abc.members on v.member_Id equals m.member_Id where Convert.ToDateTime(v.visit_Date) >= startdate && Convert.ToDateTime(v.visit_Date) <= enddate group m by new { m.member_Firstname,m.member_Lastname,m.member_Id } into g orderby g.Count() select new { numVisits = g.Count(),firstname = g.Key.member_Firstname,lastname = g.Key.member_Lastname }; 不幸的是我无法改变架构…… 我有错误: linq to entites does not recognise Convert.ToDatetime method 是否有任何可能的解决方案将字符串转换为Datetime? 更新的代码: 根据要求我更新了我的问题 var data = (from v in abc.visits join m in abc.members on v.member_Id equals m.member_Id select new { MemberID = v.member_Id,VisiteDate = v.visit_Date,FirstName = m.member_Firstname,LastName = m.member_Lastname }).ToList(); var membersdata = from d in data where Convert.ToDateTime(d.VisiteDate) >= startdate && Convert.ToDateTime(d.VisiteDate) <= enddate group m by new { d.FirstName,d.LastName,d.MemberID } into g orderby g.Count() select new { numVisits = g.Count(),firstname = g.Key.FirstName,lastname = g.Key.LastName }; 解决方法
我不认为EF支持将String转换为DateTime或反之亦然.
在我看来,你有两个选择,取决于字符串字段中日期的格式: 如果格式非常简单,那么字符串比较可能就足够了: // Convert the boundaries to strings first // TODO: Set the ToString format option to match the database format string startDateAsString = startdate.ToString("yyyyMMdd"); string endDateAsString = enddate.ToString("yyyyMMdd"); // Query based on string comparison var memberl = from v in abc.visits join m in abc.members on v.member_Id equals m.member_Id where v.visit_Date.CompareTo(startDateAsString) >= 0 && v.visit_Date.CompareTo(endDateAsString) <= 0 group m by new { m.member_Firstname,lastname = g.Key.member_Lastname }; 如果日期的字符串表示形式更复杂,并且简单的字符串比较无法提供帮助,您可以考虑在访问表上创建一个视图,该视图在数据库级别为您进行转换: CREATE VIEW VisitsWithDate (MemberId,VisitDate) AS SELECT MemberId,Convert(datetime,VisitDate,112) -- For instance FROM Visits 然后将此视图导入DataModel.您可能需要做一些魔术才能使关系发挥作用. 希望能帮助到你. (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |