Question

在我的应用程序中，我使用MS SQL Server 2008和Linq-to-SQL。我有两个表：A和B，与外键相关联：B.AId =＆gt; A.Id。在B.AId中是否有可能有一个值，例如-1，这意味着'没有A'并忽略外键？

我无法在NULL中使用B.AId，因为Linq-to-SQL不支持一对一或零关联（不幸的是）。

Answer 1

使用表A和B

创建样本模型

CREATE TABLE [dbo].[A](
    [Id] [int] NOT NULL,
    [AA] [varchar](50) NOT NULL,
    [AAA] [varchar](50) NOT NULL,
 CONSTRAINT [PK_A] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

CREATE TABLE [dbo].[B](
    [Id] [int] NOT NULL,
    [BB] [varchar](50) NOT NULL,
    [BBB] [varchar](50) NOT NULL,
    [AId] [int] NULL,
 CONSTRAINT [PK_B] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

ALTER TABLE [dbo].[B]  WITH CHECK ADD  CONSTRAINT [FK_B_A] FOREIGN KEY([AId])
REFERENCES [dbo].[A] ([Id])
GO

ALTER TABLE [dbo].[B] CHECK CONSTRAINT [FK_B_A]
GO

之后从数据库生成模型。即使它被识别为1对多关系，也会为表B创建导航属性A.

Linq-to-sql model

我创建了一个测试并在表B中创建了三个不同的行

使用导航属性A
使用A的ID

创建了一行而没有引用A

using (var db = new DataClasses1DataContext())
{
    // Add sample A row
    var sampleARow = new A()
                         {
                             Id = 1,
                             AA = "AA",
                             AAA = "AAA",
                         };

    db.As.InsertOnSubmit(sampleARow);
    db.SubmitChanges();

    // Refer to sample A row using navigation property
    var sampleNewBRowWithNav = new B()
                           {
                               Id = 1,
                               BB = "BB1",
                               BBB = "BBB1",
                               A = db.As.First(),
                           };

    // Refer to sample A row using Id
    var sampleNewBRowWithId = new B()
    {
        Id = 2,
        BB = "BB2",
        BBB = "BBB2",
        AId = 1,
    };

    // No reference to A
    var sampleNewBRowWithoutA = new B()
    {
        Id = 3,
        BB = "BB3",
        BBB = "BBB3",
        AId = null  // strictly not needed, because AId is default null
    };

    db.Bs.InsertOnSubmit(sampleNewBRowWithNav);
    db.Bs.InsertOnSubmit(sampleNewBRowWithId);
    db.Bs.InsertOnSubmit(sampleNewBRowWithoutA);

    db.SubmitChanges();
}

没有外键的外键＆＃39;值

1 个答案: