Question

我遇到了EF6和多对多关系的问题。我有以下设置：

public class Foo
{
    public int Id { get; set; }
    public virtual ICollection<Bar> Bars { get; set; }
    public virtual ICollection<SubBar> SubBars { get; set; }

    public Foo()
    {
        Bars = new HashSet<Bar>();
        SubBars = new HashSet<SubBar>();
    }
}

public class Bar
{
    public int Id { get; set; }
    public virtual ICollection<Foo> Foos { get; set; }

    public Bar()
    {
        Foos = new HashSet<Foo>();
    }
}

public class SubBar
{
    public int Id { get; set; }
    public virtual ICollection<Foo> Foos { get; set; }

    public SubBar()
    {
        Foos = new HashSet<Foo>();
    }
}

Foo和Bar之间的关系正常工作，并且数据库中有一个名为BarFoos的表。但是Foo和SubBar之间的关系是相反的。数据库中有一个名为FooSubBars的表，它基本上保持正确的关系，但是像SubBar.AsQueryable().Include(sb => sb.Foos)这样的急切加载会返回带有EntityCommandExecutionException消息的Invalid object name dbo.SubBarFoos。

问题是：如何反转关系表名称以允许急切加载？
- 编辑 -
迁移中的数据库创建如下：

CreateTable(
            "dbo.BarFoos",
            c => new
                {
                    Bar_Id = c.Int(nullable: false),
                    Foo_Id = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.Bar_Id, t.Foo_Id })
            .ForeignKey("dbo.Bars", t => t.Bar_Id, cascadeDelete: true)
            .ForeignKey("dbo.Foos", t => t.Foo_Id, cascadeDelete: true)
            .Index(t => t.Bar_Id)
            .Index(t => t.Foo_Id);

CreateTable(
            "dbo.FooSubBars",
            c => new
                {
                    Foo_Id = c.Int(nullable: false),
                    SubBar_Id = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.Foo_Id, t.SubBar_Id })
            .ForeignKey("dbo.Foos", t => t.Foo_Id, cascadeDelete: true)
            .ForeignKey("dbo.SubBars", t => t.SubBar_Id, cascadeDelete: true)
            .Index(t => t.Foo_Id)
            .Index(t => t.SubBar_Id);

在迁移中替换表名是否足够？

Answer 1

如果您在DbContext上覆盖OnModelCreating方法，则可以确保将表名生成为“FooBars”，如下所示：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Entity<Foo>().HasMany(f => f.Bars).WithMany(b => b.Foos)
            .Map(m => 
                m.ToTable("FooBars")
                // Optionally specify the key column names...
                .MapLeftKey("FooId") 
                .MapRightKey("BarId")
            );

    modelBuilder.Entity<Foo>().HasMany(f => f.SubBars).WithMany(sb => sb.Foos).Map(m => m.ToTable("FooSubBars"));
}

这将在迁移中产生这一点：

        CreateTable(
            "dbo.FooBar",
            c => new
                {
                    FooId = c.Int(nullable: false),
                    BarId = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.FooId, t.BarId })
            .ForeignKey("dbo.Foos", t => t.FooId, cascadeDelete: true)
            .ForeignKey("dbo.Bars", t => t.BarId, cascadeDelete: true)
            .Index(t => t.FooId)
            .Index(t => t.BarId);

        CreateTable(
            "dbo.FooSubBar",
            c => new
                {
                    Foo_Id = c.Int(nullable: false),
                    SubBar_Id = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.Foo_Id, t.SubBar_Id })
            .ForeignKey("dbo.Foos", t => t.Foo_Id, cascadeDelete: true)
            .ForeignKey("dbo.SubBars", t => t.SubBar_Id, cascadeDelete: true)
            .Index(t => t.Foo_Id)
            .Index(t => t.SubBar_Id);

我还尝试在DbContext上查询SubBars时急切加载Foos，但没有出现任何错误：

var context = new FooBarContext();

var subBars = from sb in context.SubBars.Include(i => i.Foos)
              select sb;

Answer 2

我可以通过查看

来反转命名

https://msdn.microsoft.com/en-us/library/jj591620(v=vs.113).aspx

只要Entity1和Entity2都具有彼此的导航属性，那么以下工作。

            modelBuilder.Entity<Order>()
                .HasMany(t => t.Products)
                .WithMany(t => t.Orders);

产生

            CreateTable(
            "dbo.OrderProducts",
            c => new
                {
                    Order_OrderID = c.Int(nullable: false),
                    Product_ID = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.Order_OrderID, t.Product_ID })
            .ForeignKey("dbo.Orders", t => t.Order_OrderID, cascadeDelete: true)
            .ForeignKey("dbo.Products", t => t.Product_ID, cascadeDelete: true)
            .Index(t => t.Order_OrderID)
            .Index(t => t.Product_ID);

实体框架多对多关系表创建“向后”

2 个答案: