Question

我有三个班级：

public class EntityBase
{
    public Guid Id { get; set; }

    [MaxLength(50)]
    public string Name { get; set; }

    public List<Tag> Tags { get; set; }
}

public class Entity : EntityBase
{
    [MaxLength(50)]
    public string Text { get; set; }
}

public class Entity1 : EntityBase
{
    [MaxLength(50)]
    public string Text2 { get; set; }
}

如果我查询基本实体并仅投影普通属性（例如，名称） - 一切都很好，派生类不会加入查询，因为不需要它们的信息。

var entities = dataContext.Entities
                .Select(e => new { Name = e.Name })
                .ToList();

将我的查询转换为：

SELECT 
1 AS [C1], 
[Extent1].[Name] AS [Name]
FROM [dbo].[EntityHeaders] AS [Extent1]

SELECT 
1 AS [C1], 
[Extent1].[Name] AS [Name]
FROM [dbo].[EntityHeaders] AS [Extent1]

但是，如果我需要获取基类的集合，则所有派生类的表都会出现在查询中。

var entities = dataContext.Entities
    .Include(e => e.Tags)
    .Select(e => new { Name = e.Name, Tags = e.Tags })
    .ToList();

我有这个

SELECT 
[Project1].[Id1] AS [Id], 
[Project1].[Id2] AS [Id1], 
[Project1].[Id] AS [Id2], 
[Project1].[C1] AS [C1], 
[Project1].[Name] AS [Name], 
[Project1].[C2] AS [C2], 
[Project1].[Id3] AS [Id3], 
[Project1].[Value] AS [Value], 
[Project1].[EntityBase_Id] AS [EntityBase_Id]
FROM ( SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Name] AS [Name], 
    [Extent2].[Id] AS [Id1], 
    [Extent3].[Id] AS [Id2], 
    1 AS [C1], 
    [Extent4].[Id] AS [Id3], 
    [Extent4].[Value] AS [Value], 
    [Extent4].[EntityBase_Id] AS [EntityBase_Id], 
    CASE WHEN ([Extent4].[Id] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C2]
    FROM    [dbo].[EntityHeaders] AS [Extent1]
    LEFT OUTER JOIN [dbo].[DerivedEntities2] AS [Extent2] ON [Extent1].[Id] = [Extent2].[Id]
    LEFT OUTER JOIN [dbo].[DerivedEntities1] AS [Extent3] ON [Extent1].[Id] = [Extent3].[Id]
    LEFT OUTER JOIN [dbo].[Tags] AS [Extent4] ON [Extent1].[Id] = [Extent4].[EntityBase_Id]
)  AS [Project1]
ORDER BY [Project1].[Id1] ASC, [Project1].[Id2] ASC, [Project1].[Id] ASC, [Project1].[C2] ASC

有可能避免这种情况吗？

如果包含至少一个基类的子集合，则查询中将包含所有派生类的EF JOIN

0 个答案: