Question

我正在尝试创建2个表。一个用于商店，一个用于收银机。收银机有复合键：Id + ShopId

这是一个模型：

public class Shop
{
    [Key]
    public int Id { get; set; }
    public string ShopName { get; set; }
}

public class CashRegister
{
    [Key, Column(Order = 0)]
    public int Id { get; set; }
    public string CashRegisterName { get; set; }

    [ForeignKey("ShopId")]
    public Shop Shop { get; set; }

    [Key, Column(Order = 1)]
    public int ShopId { get; set; }
}

以下是迁移的方式：

        CreateTable(
            "dbo.CashRegisters",
            c => new
                {
                    Id = c.Int(nullable: false),
                    ShopId = c.Int(nullable: false),
                    CashRegisterName = c.String(),
                })
            .PrimaryKey(t => new { t.Id, t.ShopId })
            .ForeignKey("dbo.Shops", t => t.ShopId, cascadeDelete: true)
            .Index(t => t.ShopId);

        CreateTable(
            "dbo.Shops",
            c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    ShopName = c.String(),
                })
            .PrimaryKey(t => t.Id);

以下是抛出主键冲突异常的代码：

        var context = new Model();

        var shops = new List<Shop>
        {
          new Shop() { ShopName = "First shop" },
          new Shop() { ShopName = "Second shop" }
        };

        context.Shops.AddOrUpdate(shops.ToArray());
        context.SaveChanges();

        var cashRegisters = new List<CashRegister>();

        foreach (var shop in shops)
        {
            cashRegisters.Add(new CashRegister()
            {
                CashRegisterName = "First cash register",
                ShopId = shop.Id
            });

            cashRegisters.Add(new CashRegister()
            {
                CashRegisterName = "Second cash register",
                ShopId = shop.Id
            });
        }

        context.CashRegisters.AddOrUpdate(a => new { a.Id, a.ShopId }, cashRegisters.ToArray());
        context.SaveChanges();
        //primary key violation exception on line above

现在显然收银机在创建时有0作为Id。我得到的例外是：

"Violation of PRIMARY KEY constraint 'PK_dbo.CashRegisters'. Cannot insert duplicate key in object 'dbo.CashRegisters'. The duplicate key value is (0, 1).\r\nThe statement has been terminated."

我尝试将[DatabaseGenerated(DatabaseGeneratedOption.Identity)]添加到CashRegister.Id 但后来我又得到了另一个异常{"Cannot insert the value NULL into column 'Id', table 'TestCompositeKeys.dbo.CashRegisters'; column does not allow nulls. INSERT fails.\r\nThe statement has been terminated."}，这很奇怪，因为Id甚至不可为空。

有谁能告诉我我做错了什么或如何解决这个问题？谢谢

Answer 1

将CashRegister.Id设置为自动增量应该可以正常工作。

public class CashRegister
{
    [Key, Column(Order = 0), DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }
    // ...

要考虑的另一件事是AddOrUpdate声明。由于Id仅在实际插入时分配，因此您无法通过Id真正比较条目。相反，您可以尝试以下方法：

context.CashRegisters.AddOrUpdate(a => new { a.ShopId, a.CashRegisterName  }, cashRegisters.ToArray());

它只会使用初始化属性进行比较，并且确实会阻止重新插入，而使用a.Id, a.ShopId时，第二次执行种子时可能会出现重复。

Answer 2

此代码

foreach (var shop in shops)
        {
            cashRegisters.Add(new CashRegister()
            {
                CashRegisterName = "First cash register",
                ShopId = shop.Id
            });

            cashRegisters.Add(new CashRegister()
            {
                CashRegisterName = "Second cash register",
                ShopId = shop.Id
            });
        }

将插入4个CashRegister对象。两个商店各两个。当ShopId设置为主键时，则CashRegister Table不能两次使用相同的ShopId。

解决方案是为每个Shop对象插入一个CashRegister对象，或从ShopId中删除主要约束。

AddOrUpdate上的EF复合主键冲突

2 个答案: