实体框架非典型1- [0..1] - 仅模型关联 - EF LINQ选择可能性 [英] Entity Framework atypical 1-[0..1] -- model-only Association -- EF LINQ select possibilities

问题描述

假设以下表格

  ParentEntities 
 ParentID 
 
 ChildEntities 
 ChildID 
 ParentID 
  

这些表在模式中没有定义FK。 >

在EF设计器中，从DB生成后，我添加一个关联：


- 父多重：1


- 孩子多重性：0或1

当我构建时，我收到错误：错误3027：没有为以下EntitySet / AssociationSet指定映射 - ParentChild

但是，如果我尝试为这样的关联配置表格映射。

 映射到ChildEntities 
父
 ParentID<  - > ParentID（父实体支持<  - >子表列）
 
子项
 ChildID<  - > ChildID（子实体支持<  - >子表列）
  

..我得到： em>错误3007：以xxx，xxx行开始映射片段的问题：列（[ParentID]）将两个片段映射到不同的概念侧属性。

为什么这是一个错误没有意义。限制目前的实施情况？

我可以通过创建1-N关联来使其工作。这不是理想的，但它的工作原理相同，只需要在一个部分添加只读子属性：

  public父类
 {
 public Child Child {get {return Childs.Any（）？ null：Childs.First（）; }} 
} 
  

这似乎是我最好的解决方案。我不得不向数据库添加一个FK以获得EF来生成关联和导航属性，但一旦添加，我就可以删除FK，并且从DB中进一步更新模型并没有删除关联或导航属性。






正在调查如何解决不关心正在建模的关联在EF中，我遇到了另一个问题。而不是只读的Child属性，我使它正常..

  public partial class Parent 
 {
 public Child Child {get;组; } 
} 
  

..但现在我需要一种从查询中实现的方法：

  var query =来自上下文中的父母.Parents 
 //无意义加入给定选择
加入小孩context.Childs 
在parents.ParentID等于child.ParentID 
选择父母; 
  

我可以选择匿名类型..

  //步骤1 
 var query =来自上下文中的父母.Parents 
在上下文中连接子项
 parents.ParentID equals child.ParentID 
 select new {Parent = parents，Child = child}; 
  

..但是我必须消耗更多的周期才能进入我的实体：

  //步骤2 
 var results = query.Select（x => {
 var parent = x。 Parent; 
 parent.Child = x.Child; 
 return parent;}）; 
  

是否有更好/简化的方式从查询选择中执行此操作，以便EF物理器可以执行此操作从逍遥游如果没有，那么我将使用Edit 1方法。

解决方案

Ef代码首先需要1-> 0..1孩子的关系具有相同的主键。
也许这是一个类似的限制在这种情况下的建模者。
两个表中都需要ParentId（Key）。

我从来没有尝试过在DB中的设计师后缀中添加这样的关系。

编辑：匹配你的EDIT2：

我会坚持的方向。使用导航属性从加入回到原始的类A和B。

  query = context.Set< JoinTable> .Where Jt => Jt.NavA.Id == ClassAId 
&& Jt.navB.Id == ClassBId）
  

如果您需要从ClassA或ClassB返回的条目，请使用select。

Suppose the following tables

 ParentEntities
    ParentID

 ChildEntities
    ChildID
    ParentID

These tables do not have a FK defined in the schema.

In EF designer, after generating from DB, I add an association:
- Parent Multiplicity: 1
- Child Multiplicity: 0 or 1

When I build, I get the error: "Error 3027: No mapping specified for the following EntitySet/AssociationSet - ParentChild"

But if I try to configure table mapping for the association like this..

Maps to ChildEntities 
  Parent
    ParentID <-> ParentID (parent entity prop <-> child table column)

  Child
    ChildID <-> ChildID (child entity prop <-> child table column)

.. I get this: Error 3007: Problem in mapping fragments starting at lines xxx, xxx: Column(s) [ParentID] are being mapped in both fragments to different conceptual side properties.

Why this is an error doesn't make sense. Limitation of the current implementation?

[EDIT 1]
I'm able to make this work by creating a 1-N association. That's not ideal, but it works just the same, just have to add a read-only child property in a partial:

public partial class Parent
{
    public Child Child { get { return Childs.Any() ? null : Childs.First(); } }
}

This seems like the best solution for me. I had to add a FK to the database to get EF to generate the association and navigation property, but once it was added I was able to remove the FK, and further updates to the model from the DB did not remove the association or Navigation properties.


[EDIT 2]
As I was investigating how to work around not caring about the association being modeled in EF, I ran into another issue. Instead of the read-only Child property I made it normal ..

public partial class Parent
{
    public Child Child { get; set; }
}

.. but now I need a way to materialize that from the query:

var query = from parents in context.Parents
            // pointless join given select
            join child in context.Childs 
                on parents.ParentID equals child.ParentID
            select parents;

I can select an anonymous type ..

// step 1
var query = from parents in context.Parents
            join child in context.Childs
                on parents.ParentID equals child.ParentID
            select new { Parent = parents, Child = child };

.. but then I've got to consume more cycles getting that into my entity:

 // step 2
 var results = query.Select(x => {
                   var parent = x.Parent;
                   parent.Child = x.Child; 
                   return parent; });

Is there a better/streamlined way to do this from the query select so the EF materializer can do it from the get-go? If not, then I'll resort to Edit 1 methodology ..

解决方案

Ef Code first requires 1->0..1 relationships for the Child to have the same primary key. Maybe this a similar restriction In the modeler in this circumstance. ParentId (Key) required in Both tables.

I have never tried adding such relationships in designer afterwords in DB first.

EDIT: to match your EDIT2:

I would stay on the direction . Use Navigation properties to get from Join back to original class A and B.

query = context.Set<JoinTable>.Where(Jt=>Jt.NavA.Id == ClassAId
                                  && Jt.navB.Id == ClassBId)

use a select if your need entries returned from either ClassA or ClassB.

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