SQL > Linq to Sql，SQL Query 工作，Linq to SQL 返回空数据集

Question

我有这个有效的 SQL 查询：

select sum(dbos.Points) as Points, dboseasons.Year 
    from dbo.StatLines dbos
    inner join dbo.Games dbog on dbog.GameId = dbos.GameId
    inner join dbo.Seasons dboseasons on dbog.Season_SeasonId = dboseasons.SeasonId
    where dbos.PlayerId = 3
    group by dboseasons.Year

它返回点数，年份 (56, 2016)

我正在尝试将其转换为 Linq 查询以与 EF 一起使用。

我有

var query =
            from dbostats in _db.StatLines
            join dbogames in _db.Games on dbostats.GameId equals dbogames.GameId
            join dboseasons in _db.Seasons on dbogames.Season.SeasonId equals dboseasons.SeasonId
            where dbostats.PlayerId == player.PlayerId
            group dbostats.Points by dboseasons.Year into g
            select new
            {
                Year = g.Key,
                Points = g.Sum()
            };
            
        playerAndStatLines.StatLinesBySeason =
            query
            .ToList()
            .Select( r => new StatsBySeason
                {
                    Season = r.Year,
                    Points = r.Points
                });
                

返回一个空的结果集。

当我查看它生成的 SQL 时，是这样的：

SELECT 
[GroupBy1].[K1] AS [Year], 
[GroupBy1].[A1] AS [C1]
FROM ( SELECT 
    [Extent3].[Year] AS [K1], 
    SUM([Extent1].[Points]) AS [A1]
    FROM   [dbo].[StatLines] AS [Extent1]
    INNER JOIN [dbo].[Games] AS [Extent2] ON [Extent1].[GameId] = [Extent2].[GameId]
    INNER JOIN [dbo].[Seasons] AS [Extent3] ON [Extent2].[Season_SeasonId] = [Extent3].[SeasonId]
    WHERE ([Extent1].[Discriminator] IN (N'StatsBySeason',N'StatLines')) AND ([Extent1].[PlayerId] = 3)
    GROUP BY [Extent3].[Year]
)  AS [GroupBy1]

正如预期的那样，在对我的数据库执行时返回一个空结果集。

问题似乎出在这一点：

([Extent1].[Discriminator] IN (N'StatsBySeason',N'StatLines')) AND 

如果我取出它并运行生成的查询，那么我会返回我的 2016, 56 结果。

这个 Extent1.Discriminator 是什么，为什么它是从我的 Linq 查询中生成的？

我的模型类：

public class PlayerAndStatLines
    {
        public PlayerWithTeam PlayerWithTeam { get; set; }
        public IEnumerable<StatsBySeason> StatLinesBySeason { get; set; }
    }


public class Season
    {
        public int SeasonId { get; set; }
        public int Year { get; set; }
    }


public class Game
    {
        public int GameId { get; set; }
        public int HomeTeamId { get; set; }
        public int AwayTeamId { get; set; }
        public int HomeScore { get; set; }
        public int AwayScore { get; set; }
        public DateTime DatePlayed { get; set; }
        public GameType GameType { get; set; }
        public int? PlayoffGameNumber { get; set; }
        public Season Season { get; set; }
    }

public class StatLines
    {
        public int StatLinesId { get; set; }
        public int GameId { get; set; }
        public int PlayerId { get; set; }
        public int TeamId { get; set; }
        public int Points { get; set; }
        public int DefensiveRebounds { get; set; }
        public int OffensiveRebounds { get; set; }
        public int Assists { get; set; }
        public int Turnovers { get; set; }
        public int Minutes { get; set; }
        public int Steals { get; set; }
        public int Blocks { get; set; }
        public int Fouls { get; set; }
        public int ThreePointFieldGoalsAttempted { get; set; }
        public int ThreePointFieldGoalsMade { get; set; }
        public int TwoPointFieldGoalsAttempted { get; set; }
        public int TwoPointFieldGoalsMade { get; set; }
        public int FreeThrowsMade { get; set; }
        public int FreeThrowsAttempted { get; set; }
        public bool Started { get; set; }
    }


public class StatsBySeason : StatLines
    {
        public int Season { get; set; }

        public string SeasonYears => Season + " / " + (Season + 1);
    }

如果我运行以下 SQL：

select Discriminator from dbo.StatLines

我得到了 2 行，都是空的。

谢谢。

Answer 1

在同一个程序集中继承实体类时要非常小心（尽可能避免）。 EF 发现派生类并决定您要使用 TPH inheritance strategy 并静默（如果您正在使用自动迁移）创建和使用 Discriminator 列，对于现有数据当然是空的并且会中断您的查询。

我看到两个选项：

• 用包含替换继承：

  public class StatsBySeason
  {
      public int Season { get; set; }
      public StatLines StatLines { get; set; }
  
      public string SeasonYears => Season + " / " + (Season + 1);
  }
  

• 让 EF 使用 Fluent 配置忽略 StatsBySeason 类：

  protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
      modelBuilder.Ignore<StatsBySeason>();
      // ...
  }
  

  或数据注释：

  [NotMapped]
  public class StatsBySeason : StatLines
  {
      // ...
  }