c# - LINQ to Entity Framework 多对多预加载问题

Question

我有以下查询:

var MyQuery = from e in ContractContext.Equipments.Include("Manufacturers")
              where e.Customers.ID == customer.ID
              select e;

一切正常，我得到了我的设备，它正确地(急切地)加载了 Manufacturers 表。但是当我尝试执行以下多对多查询时:

var MyQuery = from e in ContractContext.Equipments.Include("Manufacturers")
              where e.Customers.ID == customer.ID
              from cce in e.ContractEquipments
              where cce.Contracts.EndedOn >= DateTime.Today
              select e;

其中“ContractEquipments”是“Equipments”和“Contracts”之间的多对多查找，但是当此查询运行时，不再轻松加载 Manufacturers 表。知道如何在不执行以下操作的情况下解决此问题:

if (MyEntity.Manufacturers.IsLoaded == false) 
   MyEntity.ManufacturersReference.Load()

这个项目需要几个小时才能执行，我想减少数据库调用的次数。

编辑#1:

我也试过没有成功:

var MyQuery = from e in ContractContext.Equipments.Include("Manufacturers")
              where e.Customers.ID == customer.ID
              join cce in ContractContext.ContractEquipments 
                on e.ID equals cce.Equipments.ID
              where cce.Contracts.EndedOn >= DateTime.Today
              select e;

Answer 1

早期包含通常会在某些类型的查询中迷失方向(即额外连接等)

解决这个问题的方法是进行查询，(然后只要您返回实体即选择 e 而不是投影即选择新{...})您可以转换为 ObjectQuery 并执行包含在外面:

var MyQuery = ((from e in ContractContext.Equipments
              where e.Customers.ID == customer.ID
              from cce in e.ContractEquipments
              where cce.Contracts.EndedOn >= DateTime.Today
              select e) as ObjectQuery<Equipment>).Include("Manufacturers");

这应该有效。

如果您对这方面的更多信息感兴趣，请查看 Tip 22 - How to make Include really Include

亚历克斯