实体框架一对多和多对多关系 [英] Entity Framework one-to-many and many-to-many relationship

问题描述

我目前正在学习实体框架，但不幸地在此任务上失败了几天……我想实现以下数据库方案：

  TableA：
 ClassA_ID 
 ClassB_ID（外键-一对一）
 
 TableATableB :(一对多关系）
 ClassA_ID 
 ClassB_ID 
 
表B：
 ClassA_ID（外键-一对一）
 ClassB_ID 
  

所以我实际上想要从A类到B类的特定一对一关系，以及从A类到B类的一对多关系。

我的C＃代码如下：

A类：

  public static int idcounter; 
 [Key] 
 public int id {get;组; } 
公共虚拟List< ClassB> allClassB {get;组; } 
 public virtual ClassB currentClassB {get;组; } 
 public int？ currentClassBID {get;组; } 
 
 public ClassA（）{
 idcounter ++; 
 id = idcounter; 
 allClassB = new List< ClassB>（）; 
 currentClassB =新的ClassB（）; 
 currentClassBID = currentClassB.id; 
 MyContext.add（this）; 
} 
  

B类：

  public static int idcounter; 
 [Key] 
 public int id {get;组; } 
个公共虚拟ClassA所有者{get;组; } 
 public int？ ownerID {获取；组; } 
 
公共ClassB（ClassA a）{
 idcounter ++; 
 id = idcounter; 
所有者= a; 
 ownerID = a.id; 
} 
  

MyContext：

  public static void add（ClassA a）
 {
使用（MyContext context = new MyContext（））
 {
 context.setB。添加（a.currentClassB）; 
 context.setA.Add（a）; 
 context.SaveChanges（）; 
} 
} 
 
受保护的覆盖无效OnModelCreating（DbModelBuilder modelBuilder）
 {
 modelBuilder.Entity< ClassA>（）。HasOptional（x => x.currentClassB）.WithMany（）。HasForeignKey（x => x.currentClassBID）.WillCascadeOnDelete（false）; 
 modelBuilder.Entity< ClassB>（）。HasOptional（x => x.ClassA）.WithMany（x => x.allClassB）.HasForeignKey（x => x.ownerID）.WillCascadeOnDelete（false） ; 
} 
  

与这个问题非常相似
实体框架代码优先：如何在两个表之间创建一对多和一对一的关系？
，但是保存时我只会得到循环异常。

 无法确定相关操作的有效顺序。由于外键约束，模型要求或商店生成的
值，可能存在依赖关系
。 
  

在

<$ p $之后p> context.setA.Add（a）;


它将currentClassB添加到allClassB中，而我却没有提到过...它突然间在我不这样做时

  allClassB = new List< ClassB>（）; 
  

我在做什么错了？

解决方案

您必须使用 InverseProperty ，如下所示。

  [InverseProperty（ allClassB）] 
公共虚拟ClassB currentClassB {get;组; } 
 public int？ currentClassBID {get;组; } 
  

数据注释-InverseProperty属性：

im currently learning the entity framework and been miserably failing with this task for a couple of days... I would like to achieve the following Database Scheme:

TableA:
ClassA_ID
ClassB_ID(foreign key - one to one)

TableATableB:(one-to-many relationship)
ClassA_ID
ClassB_ID

TableB:
ClassA_ID(foreign key - one to one)
ClassB_ID

So I Actually want a specific one to one relationship from Class A to Class B and a one to many Relationship from ClassA to ClassB.

My C# Code Looks like this:

Class A:

public static int idcounter;
[Key]
public int id { get; set; }
public virtual List<ClassB> allClassB { get; set; }
public virtual ClassB currentClassB { get; set; }
public int? currentClassBID { get; set; }

public ClassA(){
    idcounter++;
    id = idcounter;
    allClassB = new List<ClassB>();
    currentClassB = new ClassB();
    currentClassBID = currentClassB.id;
    MyContext.add(this);
}

Class B:

public static int idcounter;
[Key]
public int id { get; set; }
public virtual ClassA owner { get; set; }
public int? ownerID { get; set; }

public ClassB(ClassA a){
    idcounter++;
    id = idcounter;
    owner = a;
    ownerID =  a.id;
}

MyContext:

public static void add(ClassA a)
    {
        using (MyContext context = new MyContext ())
        {
            context.setB.Add(a.currentClassB);
            context.setA.Add(a);
            context.SaveChanges();           
        }
    }

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<ClassA>().HasOptional(x => x.currentClassB ).WithMany().HasForeignKey(x => x.currentClassBID ).WillCascadeOnDelete(false);
        modelBuilder.Entity<ClassB>().HasOptional(x => x.ClassA).WithMany(x => x.allClassB).HasForeignKey(x => x.ownerID).WillCascadeOnDelete(false) ;
    }

Its pretty similar to this question Entity Framework Code First: How can I create a One-to-Many AND a One-to-One relationship between two tables? but I just get a Circular Exception when saving.

Unable to determine a valid ordering for dependent operations. Dependencies may 
exist due to foreign key constraints, model requirements, or store-generated 
values.

Its pretty weird that after

context.setA.Add(a);

it adds currentClassB into allClassB without me ever mention that... it Even suddenly does that when i dont

allClassB = new List<ClassB>();

What am I doing wrong?

解决方案

You have to use InverseProperty as shown below.

[InverseProperty("allClassB")]
public virtual ClassB currentClassB { get; set; }
public int? currentClassBID { get; set; }

DataAnnotations - InverseProperty Attribute:

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