Linq 2 SQL一对零或一对关系可能吗? [英] Linq 2 SQL One to Zero or One relationship possible?

问题描述

是否可以在Linq2SQL中创建一对零或一个关系?

Is it possible to create a one to zero or one relationship in Linq2SQL?

我的理解是，要创建一对一关系，您需要在每个表的PK上创建FK关系.

My understanding is that to create a one to one relationship you create a FK relationship on the PK of each table.

但是您不能使PK可为空，所以我不知道如何使一对零或一种关系起作用?

But you cannot make the PK nullable, so I don't see how to make a one to zero or one relationship work?

我正在使用设计器自动创建模型-所以我想知道如何设置SQL表以诱导这种关系-而不是一些自定义的ORM代码.

I'm using the designer to automatically create the model - so I would like to know how to set up the SQL tables to induce the relationship - not some custom ORM code.

推荐答案

您是部分正确的人，但是您的想法有些混乱.

You're partially correct...but your mixing things a little.

您不能使主键字段为空.那部分是正确的.但是，对象上具有一->零或一关系的外键字段可以为空.

You cannot make a primary key field null. That part is correct. But the foreign key field on the object holding the one -> zero or one relationship CAN be null.

在LINQ to SQL中，一个->零或一个关系将只是引用另一个LINQ to SQL类但允许为空的字段.

In LINQ to SQL, the one -> zero or one relationship will just be a field that references another LINQ to SQL class but allows nulls.

示例表

create table Child (
    id int identity(1,1),
    name varchar(max),
    primary key (id))

create table Parent (
    id int identity(1,1),
    childId int,
    name varchar(max),
    primary key (id),
    foreign key (childId) references Child(id))

使用这些表，您应该从父级到子级得到一个-> 0或一个，从子级到父级得到一个->许多(一个孩子可以有很多父母).

Using those tables, you should get a one -> zero or one from Parent to Child and a one -> many from Child back to Parent (one child can have many parents).

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