如何在Entity Framework 5中正确触发集合的延迟加载？ [英] How to properly trigger lazy load of collection in Entity Framework 5?

问题描述

我在应用程序中使用EF5（代码优先）。
我有一个包含一些延迟加载字段的表。

I'm using EF5 (code first) in my application. I have a table which contains a few lazy loading fields.

public class TestEntity
{
    public int Id { get; set; }

    public virtual TestEntity2 SubEntity2 { get; set; }
    public virtual TestEntity3 SubEntity3 { get; set; }

    private ICollection<SubEntity4> _subEntities;
    public ICollection<SubEntity4> SubEntities
    {
        get { return _subEntities ?? (_subEntities = new Collection<SubEntity4>()); }
        protected set { _subEntities = value; }
    }
}

当我从数据库SubEntity2和SubEntity3可以很好地加载，但是SubEntities集合不会加载，并且始终保持Count = 0。所以我强迫这样的负载：

When I'm reading this from database SubEntity2 and SubEntity3 are loading fine but SubEntities collection just won't load and it's always stay Count=0. So I'm forcing load like this:

db.Entry(queryResult).Collection(rr => rr.SubEntities).Load();

但是据我了解，此集合应该在第一次调用时由EF自动加载，就像SubEntity2和SubEntity3 。为什么它不能与集合一起使用？

But as I understand this collection should be loaded automatically by EF during the first invocation just like SubEntity2 and SubEntity3. Why isn't it working with collection?

我用来读取数据库的代码示例：

Example of the code I'm using to read database:

using (var db = new TestContext(_connection, false))
        {
            var query = from r in db.SubEntities
                        where r.Id == 10
                        select r;

            var queryRes = query.FirstOrDefault();
            if (queryRes != null)
            {
                if (queryRes.FederalRegion != null)
                {
                    // Do something
                }

                foreach (var dbEnt in queryRes.SubEntities)
                {
                    // Do something
                }
            }
        }

推荐答案

为了使延迟加载正常工作，EF5必须做一些棘手的工作。在运行时，它们创建代理类，这些代理类是从模型类派生的。在这些代理类中，它们重写导航属性以实现延迟加载机制。

In order for lazy-loading to work, EF5 has to do some tricky work. At runtime they create proxy-classes, which are derived from your model classse. Within these proxy classes they override the navigation properties to implement the lazy-loading mechanism.

您的 SubEntity2 和 SubEntity3 属性是虚拟的，因此可以覆盖它们。您的 SubEntities 属性不是虚拟的-EF5无法覆盖此属性以对其进行延迟加载。

Your SubEntity2 and SubEntity3 properties are virtual, so they can be overridden. Your SubEntities property is not virtual - EF5 can't override this property to implement lazy loading for it.

何时您将您的 SubEntities 属性设置为虚拟，就可以使用。

When you make your SubEntities property virtual it should work.

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