实体框架和强制内部联接

Question

我有Table1与以下关系(他们没有强制执行,他们只创建导航属性的关系)

Table1 (*)->(1) Table2
Table1 (*)->(1) Table3
Table1 (*)->(1) Table4
Table1 (*)->(1) Table5

使用急切的加载代码看起来像

IQueryable<Table1> query = context.Table1s;

query = query.Include(Table1 => Table1.Table2);
query = query.Include(Table1 => Table1.Table3);
query = query.Include(Table1 => Table1.Table4);
query = query.Include(Table1 => Table1.Table5);

query = query.Where(row => row.Table1Id == table1Id);

query.Single();

我尝试组织Include()语句的每一种方式,包含的第一个表在其生成的TSQL中都有一个Inner Join,剩下的就是Left Outer Join(我希望所有这些都是Left Outer).我不是实体分裂,它们只是FK的普通表.

如果DefaultIfEmpty()是唯一的解决方案,有人可以解释除了包含的第一个表之外的所有表都提供预期的SQL的原因吗？

我的理解是导航属性的默认行为是LEFT OUTER但我无法获得所有属性来生成默认值.

任何帮助将非常感激.

先感谢您!

-----创建TSQL(为简洁而修改但结构相同)-------

(@p__linq__0 int)SELECT 
[Limit1].[Table1Id] AS [Table1Id], 
[Limit1].[OtherData] AS [OtherData]
FROM ( SELECT TOP (2) 
    [Extent1].[Table1Id] AS [Table1Id], 
    [Extent1].[OtherData] As [OtherData]
    FROM       [dbo].[Table1] AS [Extent1]
    INNER JOIN [dbo].[Table2] AS [Extent2] ON [Extent1].[Table2Id] = [Extent2].[Table2Id]
    LEFT OUTER JOIN [dbo].[Table3] AS [Extent3] ON [Extent1].[Table3Id] = [Extent3].[Table3Id]
    LEFT OUTER JOIN [dbo].[Table4] AS [Extent4] ON [Extent1].[Table4Id] = [Extent4].[Table4Id]
    LEFT OUTER JOIN [dbo].[Table5] AS [Extent5] ON [Extent1].[Table5Id] = [Extent5].[Table5Id]
    WHERE [Extent1].[Table1Id] = @p__linq__0
)  AS [Limit1]

Answer 1

EF似乎INNER JOIN用于包括必需和LEFT OUTER JOIN包含可选的导航属性.例:

public class Order
{
    public int Id { get; set; }
    public string Details { get; set; }
    public Customer Customer { get; set; }
}

public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
}

如果我在... 上定义Customer为必需属性Order

public class MyContext : DbContext
{
    public DbSet<Order> Orders { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Order>()
            .HasRequired(o => o.Customer)
            .WithMany();
    }
}

...并发出此查询...

using (var ctx = new MyContext())
{
    var result = ctx.Orders
        .Include(o => o.Customer)
        .Where(o => o.Details == "Peanuts")
        .FirstOrDefault();
}

...我得到这个SQL:

SELECT TOP (1) 
[Extent1].[Id] AS [Id], 
[Extent1].[Details] AS [Details], 
[Extent2].[Id] AS [Id1], 
[Extent2].[Name] AS [Name]
FROM  [dbo].[Orders] AS [Extent1]
INNER JOIN [dbo].[Customers] AS [Extent2] 
    ON [Extent1].[Customer_Id] = [Extent2].[Id]
WHERE N'Peanuts' = [Extent1].[Details]

如果我将模型配置更改.HasRequired(o => o.Customer)为...

.HasOptional(o => o.Customer)

...我得到完全相同的查询,除了INNER JOIN [dbo].[Customers] AS [Extent2]被替换为:

LEFT OUTER JOIN [dbo].[Customers] AS [Extent2]

从模型的角度来看,它是有道理的,因为你说如果你根据需要定义关系,就永远不会Order没有a .如果您通过删除数据库中的强制执行来规避此要求,并且如果您实际上没有客户的订单则违反了您自己的模型定义.Customer

如果您遇到这种情况,只有解决方案可能会使关系成为可选关系.我不认为可以控制使用时创建的SQL Include.

Answer 2

在 EF 中，IQueryable.Include()如果没有导航属性基于强制关系，则 EF 将使用第一个表。它期望在模式中至少强制执行一个关系，并且应该使用第一个关系进行编码IQueryable.Include()，然后使用以下命令添加其他表Include()