EF表每类型带子属性表的导航属性 [英] EF Table Per Type with Navigation property on Sub Type Table

问题描述

简化背景：
我正在使用实体框架V1构建我的类结构，如下所示，我使用Table Per Type来保存我的继承对象：

  Employee 
 CaseA：案例
案例B：案例
案例分析：案例
  

CaseB有一个Navigational属性to Employee

我有一个Repository返回一个ObjectQuery。如果Case的类型实际上是CaseB，我需要在图中包含Employee对象。我不能.Include（Employee），因为它不是Case的导航属性，而Employee没有.Load（）方法。

理想情况下，我希望能够在一个查询中执行此操作，但是由于回调我很高兴我打电话，检查对象并执行另一个调用，如下所示：（尽管如前所述，load doesn'存在于员工导航资源上）

  //从
获取案例case myCase = new Repo< Case ，Entities> .FirstOrDefault（）; 
 
 if（myCase是CaseB）
（（CaseB）myCase）.Employees.load（）; 
  

我在这里缺少一些非常简单的东西？

解决方案

尝试这样：

  var employee = ctx.Cases 
。 OfType< CaseB>（）
 .Include（Employees）
 .Select（x => x.Employees）
 .FirstOrDefault（）; 
  

OfType< T>（）在EF中最重要的方法是继承 - 你应该熟悉它。

本质上是将查询中的项目过滤为特定类型 - 非常类似于您在答案中的条件检查。

这是一个 IQueryable 方法（LINQ-Objects），但在LINQ实体（ ObjectQuery< T> ），它被实现为INNER JOIN。

上述应该可以正常工作 - em> after 后，您可以执行 OfType 。

HTH。

I'm hoping someone out in the SO community will be able to help me out here.

Simplified Background: I'm using Entity Framework V1 to build my class structure that is outlined below, I'm using Table Per Type to persist my inherited objects:

Employee 
CaseA : Case
CaseB : Case
CaseC : Case

CaseB has a Navigational Property to Employee

I have a Repository that returns an ObjectQuery. If the type of Case is actually CaseB, I need to include the Employee object within the graph. I can't .Include("Employee") because it's not a navigational property of Case, and Employee doesn't have a .Load() method on it.

Ideally I want to be able to do this in one query, however as a fall back I'm happy that I make a call, check the Object and perform another call, something like this: (although as I stated earlier, load doesn't exist on the employee navigational property)

    //Get the case from the 
    Case myCase = new Repo<Case, Entities>.FirstOrDefault();

    if(myCase is CaseB)
       ((CaseB)myCase).Employees.load();

Am I missing something really simple here?

解决方案

Try this:

var employee = ctx.Cases
                  .OfType<CaseB>()
                  .Include("Employees")
                  .Select(x => x.Employees)
                  .FirstOrDefault();

OfType<T>() is one of the most important methods in EF when it comes to inheritance - you should familiarize yourself with it.

Essentially is filters the items in the query to be of a particular type - very similar to the conditional check your doing in your answer.

It's an IQueryable method (LINQ-Objects), but in LINQ-Entities (ObjectQuery<T>), it get's implemented as an INNER JOIN.

The above should work - just make sure you do the eager load after you do the OfType.

HTH.

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