Question

我还是LINQ的新手，我遇到了一些麻烦。我认为这一切都搞砸了，但我有一个包含几个属性的模型，以及一个不同类型的对象（Project）。我收到一个错误：无法将'AnonymousType＃1'类型转换为'string'。我希望能够从我的NotificationModel对象中引用的ProjectModel对象中选择ProjectId和ProjectName。这就是我所拥有的，但这不起作用，我怎样才能改变它以正确地从ProjectModel对象中获取信息？

通知模型：

public int id { get; set; }
public int ProjectId { get; set; }
public string ProjectName { get; set; }
[StringLength(50)]
public string CreatedBy { get; set; }
public Nullable<System.DateTime> CreatedDateTime { get; set; }
public Nullable<bool> IsDeleted { get; set; 

public virtual ProjectModel Project { get; set; }

尝试检索数据：

        var notifications = (from a in db.NotificationsLog
                            where a.CreatedBy == userID
                            orderby a.CreatedDateTime ascending
                            select new NotificationModel
                            {
                                id = a.id,
                                ProjectId =  from p in db.Projects
                                          select new
                                                    {
                                                        ProjectId = p.ProjectId
                                                    }
                                ProjectName = from p in db.Projects
                                          select new

                                                    {
                                                        ProjectName = p.ProjectName
                                                    }
                                Notes = a.Notes;
                            });

Answer 1

如果Notification实体上的导航属性为Project，则可以执行以下操作：

var notifications = 
    (from a in db.NotificationsLog
     let p = a.Project
     where a.CreatedBy == userID
     orderby a.CreatedDateTime ascending
     select new NotificationModel
     {
         id = a.id,
         ProjectId = p.Id,
         ProjectName = p.Name,
         Project = new ProjectModel
         {
             ProjectId = p.Id
             ProjectName = p.Name
             Notes = a.Notes;
         }
     });

Answer 2

var notifications = from a in db.NotificationsLog
                    join p in db.Projects on a.ProjectId equals p.ProjectId
                    where a.CreatedBy == userID
                    select new NotificationModel
                            {
                                id = a.id,
                                ProjectId = p.ProjectId,
                                ProjectName = p.ProjectName,
                                Notes = a.Notes
                            };

在linq查询中选择来自不同对象的数据

2 个答案: