左外连接 Linq 到具有 MVC 模型的实体

Question

我对此进行了研究，如果重复，我深表歉意，但我似乎找不到正确的答案，我从这个网站学到了很多东西。

我有 3 张桌子：

CREATE TABLE [Reporting].[ReportingCompanies](
[ID] [int] IDENTITY(1,1) NOT NULL,
[EINC] [int] NOT NULL,
[CompanyId] [varchar](4) NOT NULL,
[CompanyName] [varchar](50) NOT NULL,
[LastClosedWeek] [datetime] NOT NULL,
[PriorWeekSales] [decimal](14, 4) NULL,
[PriorWeek] [datetime] NULL,
[CurrentWeek] [datetime] NULL,
[LastWeekSales] [decimal](14, 4) NULL,
[AgingBalance] [decimal](14, 4) NULL,
[DataAsOf] [datetime] NULL,
[Tier] [int] NULL,
[CurrentWeeklyAverage] [decimal](14, 4) NULL,
[AvgAged] [decimal](14, 4) NULL,
[hasSpread] [bit] NULL,
[DSO] [int] NULL,
[isFamily] [bit] NULL,
[ImportStatus] [bit] NULL,
[ClientStatus] [varchar](50) NULL,
 CONSTRAINT [PK_ReportingCompanies] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF,        ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
 ) ON [PRIMARY]

CREATE TABLE [Reporting].[AllowedCompanies](
[ID] [int] IDENTITY(1,1) NOT NULL,
[CustomUserProfileUserId] [uniqueidentifier] NOT NULL,
[CustomUserProfileID] [int] NOT NULL,
[ReportingCompanyID] [int] NOT NULL,
 CONSTRAINT [PK_AllowedCompanies] PRIMARY KEY CLUSTERED 
(
[ID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

CREATE TABLE [Reporting].[CustomUserProfiles](
[ID] [int] IDENTITY(1,1) NOT NULL,
[ApplicationId] [uniqueidentifier] NOT NULL,
[UserId] [uniqueidentifier] NOT NULL,
[UserName] [nvarchar](256) NOT NULL,
[LoweredUserName] [nvarchar](256) NOT NULL,
[MobileAlias] [nvarchar](16) NULL,
[IsAnonymous] [bit] NOT NULL,
[LastActivityDate] [datetime] NOT NULL,
[ImportStatus] [bit] NULL,
 CONSTRAINT [PK_CustomUserProfiles] PRIMARY KEY CLUSTERED 
(
[UserId] ASC,
[ID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
 ) ON [PRIMARY]

我现在需要使用左外连接添加第 4 个表，以便仅在不存在记录时为 VisitCount 列获取默认值 0。

CREATE TABLE [PayJot].[FavoriteClients](
[FavRowID] [int] IDENTITY(1,1) NOT NULL,
[Userid] [uniqueidentifier] NOT NULL,
[CompanyId] [int] NOT NULL,
[VisitCount] [int] NOT NULL,
 CONSTRAINT [PK_FavoriteClients] PRIMARY KEY CLUSTERED 
(
    [FavRowID] ASC
 )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

这是我的最新尝试，它返回错误“无法在 LINQ to Entities 查询中构造实体或复杂类型 'DALModel.FavoriteClient'”，但这正是智能感知似乎要求的 (?)

            var userName = HttpContext.Current.User.Identity.Name;

        var q = from c in db.ReportingCompanies1
                join a in db.AllowedCompanies on new { ID = (int)c.ID } equals new { ID = a.ReportingCompanyID }
                join p in db.CustomUserProfiles on new { CustomUserProfileID = a.CustomUserProfileID } equals new { CustomUserProfileID = p.ID }

                join f in db.FavoriteClients on new { A = c.ID, B = p.UserId } equals new { A = f.CompanyId, B = f.Userid } into fvc
                from userfavs in fvc.DefaultIfEmpty(new FavoriteClient { CompanyId = c.ID, Userid = p.UserId , VisitCount = 0  })

                where
                  p.UserName == userName
                orderby c.CompanyName
                select new Clients()
                {
                    ID = c.ID,
                    CompanyId = c.CompanyId,
                    CompanyName = c.CompanyName,
                    visitCount = userfavs.VisitCount
                };

            ObservableCollection<Clients> clientList = new ObservableCollection<Clients>(q.ToList());

我对 Linq 还很陌生，虽然我读过的所有示例都按照解释说得很有道理，但它们在实施中却惨遭失败。如果可以，请提前告知。

Answer 1

我刚刚开始工作：

        var q = from p in db.CustomUserProfiles
                join a in db.AllowedCompanies on new { ID = p.ID } equals new { ID = a.CustomUserProfileID }
                join c in db.ReportingCompanies1 on new { ReportingCompanyID = (int)(int)a.ReportingCompanyID } equals new { ReportingCompanyID = c.ID }
                join f in db.FavoriteClients
                      on new { a.CustomUserProfileUserId, ReportingCompanyID = a.ReportingCompanyID }
              equals new { CustomUserProfileUserId = (Guid)f.Userid, ReportingCompanyID = f.CompanyId } into FavoriteClients_join
                from FavoriteClients in FavoriteClients_join.DefaultIfEmpty()
                where
                    p.UserName == userName
                orderby
                    FavoriteClients.VisitCount descending, 
                    c.CompanyName
                select new Clients()
                {
                    ID = c.ID,
                    CompanyId = c.CompanyId,
                    CompanyName = c.CompanyName,
                    visitCount = ((Int32?)FavoriteClients.VisitCount ?? (Int32)0)
                };