Entity Framework 6.1.3：Projection - 直接加载children的children

Question

我的目标是只访问一次数据库，并通过过滤的子集合获取订单。

为了实现这一点，我使用了投影：

using (var db = new context())
            {
                var query = from o in db.Orders
                           select
                               new
                               {
                                   Order = o,
                                   Events = o.Events.Where(
                                       e => e.SomeBool 
                                       && e.SomeBool2
                                   ),

                                   EventsGroups = o.Events.Where(
                                       e => e.SomeBool 
                                       && e.SomeBool2
                                   ).Select(e => e.Groups),

                               };
            }

这里的问题是子集合“组”事件没有加载。为了解决这个问题，我在查询中将它作为另一个属性“EventsGroups”加载，然后我可以将其与事件放在一起。

我的问题：有没有办法将孩子“组”直接加载到“事件”上，这样我就不必将它们作为另一个属性获取？

沿线

Events = o.Events.Where(
e => e.SomeBool 
&& e.SomeBool2
).Include(e => e.Groups), //this cannot be done this way

---

为什么我使用投影而不是预先加载：

https://msdn.microsoft.com/en-us/magazine/hh205756.aspx

Filtering include items in LINQ and Entity Framework

底层类：

public class Order
{
    public Order()
    {
        Events = new HashSet<Event>();
    }

    public int Id { get; set; }

    public virtual ICollection<Event> Events { get; set; }
}

public class Event
{
    public Event()
    {
        Groups = new HashSet<Group>();
    }

    public int Id { get; set; }

    public bool SomeBool { get; set; }

    public bool SomeBool2 { get; set; }

    public virtual ICollection<Group> Groups { get; set; }
}

public class Group
{
    public Group()
    {
        Events = new HashSet<Event>();
    }

    public int Id { get; set; }

    public string Name { get; set; }

    public virtual ICollection<Event> Events { get; set; }
}

Answer 1

由于Include不能与匿名投影结合，您需要像投影Order.Events一样投影Event.Groups，即使用另一种匿名类型投影：

var query = from o in db.Orders
            select new
            {
                Order = o,
                Events = (from e in o.Events
                          where e.SomeBool && e.SomeBool2
                          select new
                          {
                              Event = e,
                              Groups = e.Groups,
                          }),
            };

Answer 2

您可以通过设置 Configuration.LazyLoadingEnabled = true; 来加载所有内容，而不需要任何 Include ，当然...性能必须牢记..取决于..

    public MyDatabaseContext(string databaseName)
        : base(databaseName)
    {
        Configuration.LazyLoadingEnabled = true;
    }

Answer 3

我相信这应该适合你：

using (var db = new context())
{
  var query = db.Orders
    .Include(o=>o.Events)
    .Include(o=>o.Events.Select(e=>e.Groups))
    .Select(o=>new
    {
      Order = o,
      Events = o.Events.Where(e => e.SomeBool && e.SomeBool2)
    });
}

如果没有，这将：

using (var db = new context())
{
  var query = db.Orders
    .Include(o=>o.Events)
    .Include(o=>o.Events.Select(e=>e.Groups))
    .Select(o=>new Order
    {
      Id=o.Id,
      Events = o.Events.Where(e => e.SomeBool && e.SomeBool2).ToList()
    });
}