列出实体框架中外键指向的实体

I have two Entities, let's say Car and Photo. Each photo has foreign key to Car, so each car has set of its photos.

我有两个实体，比方说汽车和照片。每张照片都有Car的外键，所以每辆车都有一套照片。

I want to list some subset of cars and for each listed car I want to list all of each photos.

我想列出一些汽车的子集，对于每辆列出的汽车，我想列出所有每张照片。

How can I do this in Entity Framework with 1 db query? I know from the beginning that I would need photos.

如何在1 db查询的Entity Framework中执行此操作？我从一开始就知道我需要照片。

My code for now look like:

我的代码现在看起来像：

var carList = CarEntities.Where(...).ToList();
foreach(var car in carList){
    var photoList = car.Photos.ToList();
}

I think, EF would do separately db query for each car.

我想，EF会为每辆车单独进行数据库查询。

3 个解决方案

#1

You can tell Entity Framework in include Photos when querying Cars.

在查询汽车时，您可以在实体框架中包含照片。

var carList = CarEntities.Include(c => c.Photos).Where(...).ToList();

#2

ckal's answer is pretty close except use include in the end otherwise EF may not always include it (cant recall exact reason at the moment),

ckal的答案非常接近，除非最后使用包括在内，否则EF可能并不总是包含它（暂时不能回想起原因），

var carList = CarEntities.Where(...).Include(c => c.Photos).ToList();

Edit: Here's the reason... Entity Framework Include() is not working

编辑：这是原因...实体框架Include（）不起作用

#3

"Select new" is what you likely want to do. Create a new class called CarWithPhotos and use that to return a set of results:

“选择新”是您可能想要做的。创建一个名为CarWithPhotos的新类，并使用它来返回一组结果：

var carWithPhotos = from car in CarEntities
                    where (...) 
                    select new CarWithPhotos(car, car.Photos.ToList());

As I understand it, this compiles to one a single database trip, which I think is what you're after.

据我所知，这可以编译成一个单一的数据库之旅，我认为这就是你所追求的。

Edit: I've used this technique when the objects I'm querying are large and I don't always want to retrieve an entire "Car" object for example.

编辑：当我查询的对象很大并且我并不总是想要检索整个“Car”对象时，我使用了这种技术。

#1