c# - 由于类型不匹配，LINQ Join 失败

Question

我需要来自 2 个不同数据库的数据。我试过以下

var User = (from U in _db.TblUsers
                        where U.IsAdmin == false
                        select U).ToList();

var AspNewsUser = (from A in _dbAspNet.aspnet_Users                        
                   select A).ToList();


var result = (from U in User
              join A in AspNewsUser
              on U.UserID equals A.UserId
              select U);

但我收到以下错误消息

join 子句中的表达式之一的类型不正确。对“加入”的调用中的类型推断失败。

Answer 1

正如您在aspnet_Users 的表架构中看到的那样，Userid是一个uniqueidentifier（映射到实体框架中的 GUID）。我敢打赌，TblUsers.UserID它有不同的类型（如int）。

Answer 2

使用投影，使它们成为相同的匿名类型。

    var Users = (from U in _db.TblUsers
                    where U.IsAdmin == false
                    select new { UserID = U.UserID }).ToList();

    var AspNewsUsers = (from A in _dbAspNet.aspnet_Users                        
                    select new { UserID = A.UserID }).ToList();


    var result = (from i in Users join o in AspNewUsers on i.UserID equals o.UserID).ToList();