Question

因此，假设我有以下实体及其上下文配置，如下所示。为简洁起见，我省略了很多属性：

public class Company {
    public int Id { get; set; }
    public Location Location { get; set; }
}

public class Customer {
    public int Id { get; set; }
    public Location Location { get; set; }
}

public class Location {
    public int Id { get; set; }
}

public sealed class EntityDefaultContext : DbContext {
    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        modelBuilder.Entity<Company>().HasKey(m => m.Id).ToTable("Company");
        modelBuilder.Entity<Company>().Property(m => m.Id).HasColumnName("Id");
        modelBuilder.Entity<Company>().HasRequired(m => m.Location).WithRequiredDependent().Map(m => m.MapKey("LocationId"));

        modelBuilder.Entity<Customer>().HasKey(m => m.Id).ToTable("Customer");
        modelBuilder.Entity<Customer>().Property(m => m.Id).HasColumnName("Id");
        modelBuilder.Entity<Customer>().HasRequired(m => m.Location).WithRequiredDependent().Map(m => m.MapKey("LocationId"));

        modelBuilder.Entity<Location>().HasKey(m => m.Id).ToTable("Location");
        modelBuilder.Entity<Location>().Property(m => m.Id).HasColumnName("Id");
    }
}

如您所见，公司和客户实体都持有对Location实体的引用。我相信通常会发生的事情。

我为您设置了我的数据库上下文，您也可以看到。但EF生成的SQL非常低效：

SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[LocationId] AS [LocationId], 
    [Extent3].[Id] AS [Id1]
FROM
    [dbo].[Customer] AS [Extent1]
LEFT OUTER JOIN [dbo].[Company] AS [Extent2] ON [Extent1].[LocationId] = [Extent2].[LocationId]
LEFT OUTER JOIN [dbo].[Company] AS [Extent3] ON [Extent1].[LocationId] = [Extent3].[LocationId]
LEFT OUTER JOIN [dbo].[Company] AS [Extent4] ON [Extent1].[LocationId] = [Extent4].[LocationId]

这是在我做这样的事情时产生的：

var q = from c in defaultContext.Set<Customer>().Include(m => m.Location)
        select c;

我这样做的原因与问题无关。奇怪的是，如果我仅将Location实体配置为仅由Customer实体关联，那么这是SQL：

SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[LocationId] AS [LocationId]
FROM
    [dbo].[Customer] AS [Extent1]
INNER JOIN [dbo].[Location] AS [Extent2] ON [Extent1].[LocationId] = [Extent2].[Id]

这是我所期待的。这让我想到了。 EF不支持这种情况吗？怎么可能不是？

提前致谢。

Answer 1

您的原始映射使用一对一关系。这总会导致一些特殊的行为。此外，它还有一些其他要求才能正常工作。您可能想要的是Customer和Location以及Company和Location之间的一对多关系。将WithRequiredDependent更改为WithMany，它应该有效。

一个实体可以由超过1个实体关联吗？

1 个答案: