EFCore关系配置

た入场券 2024-03-27 10:41 82阅读 0赞

### 一、EFCore中一对多关系数据的获取 ###

#### 获取id为1的信息以及它对应的Comments ####

代码如下

![e7ce0b6d83b945d385a519fd72927f88.png][]

输出结果为：

![a23fa4a1f64341149d7e4fddf32bdc16.png][]

并没有查询到对应的comments

断点查看

![49cf569c3277493fb6a985ada41f5f9f.png][]

断电查看Comments并没有查出来

查看select语句

>     SELECT TOP(2) [t].[Id], [t].[Message], [t].[Title]
>           FROM [T_Articles] AS [t]
>           WHERE [t].[Id] = CAST(1 AS bigint)

发现只查询了一个表 并没有查询**T\_Comment**表

这时候需要修改语句

![52dbf645d6264dc385d8d2f076bea65a.png][]

>     Article article = context.Articles.Include(a => a.comments).Single(a => a.Id == 1);

意思是把Article的comments属性关联查询出来

运行结果

![6cd68fd0bed7415092086f3ba72c1214.png][]

查看select语句

>     SELECT [t0].[Id], [t0].[Message], [t0].[Title], [t1].[Id], [t1].[Message], [t1].[TheArticleId]
>           FROM (
>               SELECT TOP(2) [t].[Id], [t].[Message], [t].[Title]
>               FROM [T_Articles] AS [t]
>               WHERE [t].[Id] = CAST(1 AS bigint)
>           ) AS [t0]
>           LEFT JOIN [T_Comments] AS [t1] ON [t0].[Id] = [t1].[TheArticleId]
>           ORDER BY [t0].[Id]

发现两个表使用join连接

**include作用是把关联的对象也给查询出来**

### 二、一对一 ###

#### 一对一关系配置 ####

builder.HasOne<Delivery>(o => o.Delivery).WithOne(d => d.Order).HasForeignKey<Delivery>(d => d.OrderId);

一个订单对应一个快递单 一个快递单对应一个订单

一对一必须在其中一个实体类中声明一个外键属性

[e7ce0b6d83b945d385a519fd72927f88.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/17c4e3e8985349ada641deef36584bb7.png
[a23fa4a1f64341149d7e4fddf32bdc16.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/c5bb46d292a0416b99a7bced03be2fe8.png
[49cf569c3277493fb6a985ada41f5f9f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/ca6abb26b5a64f4eb0efa401c0b29630.png
[52dbf645d6264dc385d8d2f076bea65a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/e88e22ad553a4101af3d00cadc084d90.png
[6cd68fd0bed7415092086f3ba72c1214.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/575c50ec06d0476babd93683590be1e5.png