Question

我一直在打开和关闭这个，我真的不知道我做错了什么或者这是EF Core的错误，基本上问题是我的查询有两个连接总是返回零结果，我尝试以各种不同的方式重写它无济于事（我只是得到各种不同的错误）并且如果它只是一个错误我不想继续战斗它。但是，查询在LINQPad中按预期工作。查询如下：

var playerholder = (from player in db.Players
                    join assignment in db.TeamAssignments on player.PlayerID equals assignment.PlayerID into assignments
                    from assignment in assignments.DefaultIfEmpty()
                    join team in db.Teams on assignment == null ? 0 : assignment.TeamID equals team.TeamID into teams
                    from team in teams.DefaultIfEmpty()
                    select new PlayerListItem_PDVMI
                    {
                        PlayerID = player.PlayerID,
                        FirstName = player.FirstName,
                        LastName = player.LastName,
                        TeamName = (assignment == null ? "Not Assigned" : team.Name)
                    }).ToList();

如果玩家可以拥有0个或更多TeamAssignments，而TeamAssignment只有一个团队。

从我的日志文件中生成的SQL。这也可以直接在数据库上运行时正常运行：

SELECT [assignment].[ID], [assignment].[PlayerID], [assignment].[PlayerNumber], [assignment].[Position], [assignment].[SeasonID], [assignment].[TeamID], [player].[PlayerID], [player].[FirstName], [player].[LastName]
FROM [Players] AS [player]
LEFT JOIN [TeamAssignments] AS [assignment] ON [player].[PlayerID] = [assignment].[PlayerID]
ORDER BY [player].[PlayerID]

并且紧接着就是对Teams表的查询：

SELECT [assignment.Team].[TeamID], [assignment.Team].[Name]
FROM [Teams] AS [assignment.Team]

这是我的TeamAssignment类（删除了不相关的属性）：

public class TeamAssignment : IModel
{
    [Key]
    public int ID { get; set; }

    public int PlayerID { get; set; }

    public int TeamID { get; set; }

    [ForeignKey("PlayerID")]
    public virtual Player Player { get; set; }

    [ForeignKey("TeamID")]
    public virtual Team Team { get; set; }
}

小组：

public class Team : IModel
{
    [Key]
    public int TeamID { get; set; }

    public string Name { get; set; }

    public virtual ICollection<TeamAssignment> CurrentPlayers { get; set; }

}

播放器：

public class Player : IModel
{
    [Key]
    public int PlayerID { get; set; }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public virtual ICollection<TeamAssignment> TeamAssignments { get; set; }

}

带有连接的LINQ查询返回0结果（潜在错误）

0 个答案: