跨多个关系级别的实体框架查询 [英] Entity Framework query across multiple levels of relationship

问题描述

我才刚开始使用Entity Framework和Linq To Entities，并试图使我的头转向查询.

I'm just beginning in Entity Framework and Linq To Entities and am trying to get my head around querying.

我的数据结构如下:

表A，B，C

A与B有一对多的关系，B与C有一对多的关系.

A has one to many relationship to B, B has one to many relationship to C.

我们的一个演示对象由A，B和A的数据组成. C给出了C的ID

One of our presentation objects is composed of data from A, B & C given the Id from C

那么，如何在查询中表示呢?

So, how can I represent this in a query?

如何从where c.Id == myParam查询中获得A实体?

How do I get an A entity from a where c.Id == myParam query?

推荐答案

有关:

var c = context.Cs.Include("B.A").Where(c => c.Id == myParam).SingleOrDefault();

B是C上B实例的导航属性，而A是B到A实例的导航属性.

Where B is navigation property on C to instance of B an A is navigation property from B to instance of A.

如果System.Data.Entity命名空间得到重新引用，您也可以使用lambda表示法:

You can also use lambda notation if System.Data.Entity namespace is refeneced:

var c = context.Cs.Include(i=>i.B.A).Where(c => c.Id == myParam).SingleOrDefault();

对于Collection导航属性，您可以使用.Select()

And for Collection navigation properties you can use .Select()

var c = context.Cs.Include(i=>i.Select(j=>j.A)).Where(c => c.Id == myParam).SingleOrDefault();

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