实体框架代码优先一对多做错查询？答案

【问题标题】：Entity Framework Code First One-To-Many doing wrong queries?实体框架代码优先一对多做错查询？
【发布时间】：2011-08-19 04:31:41
【问题描述】：

所以我有一个模型

public class Player
{
    public int PlayerId { get; set; }

    [Required]
    public string Name2 { get; set; }

    public string Cv { get; set; }

    public int TeamId { get; set; }
    public virtual Team Team { get; set; }
}



public class Team
{
    public int TeamId { get; set; }
    [Required]
    public string Name { get; set; }
    public string City { get; set; }
    public DateTime Founded { get; set; }

    public virtual IList<Player> Players { get; set; }
}

我在 DB 中的 Teams 表包含记录，我在 DB 中的 Players 表不包含任何记录（空）。

当我运行这个查询时：

        IQueryable<Player> query = playerRepository.All.Include(p => p.Team);

        return View((query);

我在数据库中得到这个查询（通过分析器）：

SELECT 
[Project1].[TeamId] AS [TeamId], 
[Project1].[Name] AS [Name], 
[Project1].[City] AS [City], 
[Project1].[Founded] AS [Founded], 
[Project1].[C1] AS [C1], 
[Project1].[PlayerId] AS [PlayerId], 
[Project1].[Name2] AS [Name2], 
[Project1].[Cv] AS [Cv], 
[Project1].[TeamId1] AS [TeamId1]
FROM (  SELECT 
            [Limit1].[TeamId] AS [TeamId], 
            [Limit1].[Name] AS [Name], 
            [Limit1].[City] AS [City], 
            [Limit1].[Founded] AS [Founded], 
            [Extent2].[PlayerId] AS [PlayerId], 
            [Extent2].[Name2] AS [Name2], 
            [Extent2].[Cv] AS [Cv], 
            [Extent2].[TeamId] AS [TeamId1], 
            CASE    WHEN ([Extent2].[PlayerId] IS NULL) THEN CAST(NULL AS int) 
                    ELSE 1 
            END AS [C1]
        FROM   (    SELECT TOP (10) [c].[TeamId] AS [TeamId], 
                                    [c].[Name] AS [Name], 
                                    [c].[City] AS [City], 
                                    [c].[Founded] AS [Founded]
                      /* HERE */    
                      FROM [dbo].[Teams] AS [c] 
                ) AS [Limit1]
        /* AND HERE */
        LEFT OUTER JOIN [dbo].[Players] AS [Extent2] 
        ON              [Limit1].[TeamId] = [Extent2].[TeamId]
)  AS [Project1]
ORDER BY [Project1].[TeamId] ASC, [Project1].[C1] ASC

结果我在屏幕上显示了一个空行。这是因为这种加入是以错误的顺序完成的......而不是加入 Teams on Players，我得到了 Players on Teams......这反过来意味着即使我在数据库中没有玩家，我在网格。

有人知道为什么吗？？？

弗拉丹

【问题讨论】：

TOP(10) 是从哪里来的？您的存储库背后隐藏着什么？
没有逻辑...这里是方法： public IQueryable All { get { return context.Players; } }

标签： entity-framework linq-to-entities ef-code-first code-first entity-framework-4.1

【解决方案1】：

您一定是做错了什么，或者您正在查看错误的查询。我使用了你的实体和你的 linq 查询：

var data = context.Players.Include(p => p.Team).ToList();

我得到了这个 SQL 查询：

SELECT 
[Extent1].[PlayerId] AS [PlayerId], 
[Extent1].[Name2] AS [Name2], 
[Extent1].[Cv] AS [Cv], 
[Extent1].[TeamId] AS [TeamId], 
[Extent2].[TeamId] AS [TeamId1], 
[Extent2].[Name] AS [Name], 
[Extent2].[City] AS [City], 
[Extent2].[Founded] AS [Founded]
FROM  [dbo].[Players] AS [Extent1]
INNER JOIN [dbo].[Teams] AS [Extent2] ON [Extent1].[TeamId] = [Extent2].[TeamId]

但是如果我使用这个查询：

var data = context.Teams.Include(t => t.Players).Take(10).ToList();

我会准确地得到您的 SQL 查询。 TOP (10)和逆向表查询不会无故出现。

【讨论】：