实体框架代码首先 - 定义此EntityType的键 [英] Entity Framework Code-First - Define the key for this EntityType

问题描述

我打算在我的一个项目中测试EF Code First。这是我想要的。
我有三个表，结构如下

  public partial class App_user 
 {
 public int id {get;组; } 
 public string name {get;组; } 
 public string email_address {get;组; } 
 public string password {get;组; } 
 public int user_type {get;组; } 
 public List< Role>角色{get;组; } 
} 
 
 public partial class Role 
 {
 public int id {get;组; } 
 public string name {get;组; } 
} 
 public partial class User_role 
 {
 public int user_id {get;组; } 
 public int role_id {get;组; } 
 public virtual Role Role {get;组; } 
 public virtual App_user App_user {get;组; } 
} 
  

在第三个表中没有主键。所以运行时会出错。以下是错误消息 -

System.Data.Edm.EdmEntityType：：
EntityType'User_role'没有键
定义。定义此
EntityType的键。
System.Data.Edm.EdmEntitySet：
EntityType：EntitySet User_roles
基于没有定义
键的User_role类型。

< blockquote>

为什么它发生了？是否有解决方案？

解决方案

如果您试图建立用户和角色之间的多对多关系。在这种情况下，您的模型是完全错误的。

使用此代替：

  public partial class App_user 
 {
 public int id {get;组; } 
 public string name {get;组; } 
 public string email_address {get;组; } 
 public string password {get;组; } 
 public int user_type {get;组; } 
 public virtual ICollection< Role>角色{get;组; } 
} 
 
 public partial class Role 
 {
 public int id {get;组; } 
 public string name {get;组; } 
 public virtual ICollection< User>用户{get;组; } 
} 
  

这将自动创建多对多，您不需要麻烦连接台。如果你需要暴露连接表，你必须使用这个：

  public partial class App_user 
 {
 public int id {get;组; } 
 public string name {get;组; } 
 public string email_address {get;组; } 
 public string password {get;组; } 
 public int user_type {get;组; } 
 public virtual ICollection< User_Role> UserRoles {get;组; } 
} 
 
 public partial class Role 
 {
 public int id {get;组; } 
 public string name {get;组; } 
 public virtual ICollection< User_Role> UserRoles {get;组; 
 
 
 public partial class User_role 
 {
 [Key，ForeignKey（App_user），Column（Order = 0）] 
 public int user_id {get;组; } 
 [Key，ForeignKey（Role），Column（Order = 1）] 
 public int role_id {get;组; } 
 public virtual Role Role {get;组; } 
 public virtual App_user App_user {get;组; } 
} 
  

如果您不需要其他属性，则露出连接表是无意义的。

对于您的错误 - Entity框架中的每个实体都必须定义主键。

Hi I'm planning to test EF Code First in one of my project. This is what I want actually. I have three tables and the structure is as follows

public partial class App_user
    {
        public int id { get; set; }
        public string name { get; set; }
        public string email_address { get; set; }
        public string password { get; set; }
        public int user_type { get; set; }
        public List<Role> Roles { get; set; }
    }

public partial class Role
    {
        public int id { get; set; }
        public string name { get; set; }
    }
public partial class User_role
    {
        public int user_id { get; set; }
        public int role_id { get; set; }
        public virtual Role Role { get; set; }
        public virtual App_user App_user { get; set; }
    }

In the third table there is no primary key. So it gives an error while running. Here is the error message -

System.Data.Edm.EdmEntityType: : EntityType 'User_role' has no key defined. Define the key for this EntityType. System.Data.Edm.EdmEntitySet: EntityType: The EntitySet User_roles is based on type User_role that has no keys defined.

Why its is happening? Is there a solution for this?

解决方案

If think you are trying to model many-to-many relation between user and role. In such case your model is completely wrong.

Use this instead:

public partial class App_user
{
    public int id { get; set; }
    public string name { get; set; }
    public string email_address { get; set; }
    public string password { get; set; }
    public int user_type { get; set; }
    public virtual ICollection<Role> Roles { get; set; }
}

public partial class Role
{
    public int id { get; set; }
    public string name { get; set; }
    public virtual ICollection<User> Users { get; set; }
}

This will create many-to-many automatically and you will not need to bother with junction table. If you need to expose junction table you must use this:

public partial class App_user
{
    public int id { get; set; }
    public string name { get; set; }
    public string email_address { get; set; }
    public string password { get; set; }
    public int user_type { get; set; }
    public virtual ICollection<User_Role> UserRoles { get; set; }
}

public partial class Role
{
    public int id { get; set; }
    public string name { get; set; }
    public virtual ICollection<User_Role> UserRoles { get; set; }
}

public partial class User_role
{
    [Key, ForeignKey("App_user"), Column(Order = 0)]
    public int user_id { get; set; }
    [Key, ForeignKey("Role"), Column(Order = 1)]
    public int role_id { get; set; }
    public virtual Role Role { get; set; }
    public virtual App_user App_user { get; set; }
}

Exposing junction table is meaningless if you don't need additional properties in it.

To your error - each entity in Entity framework must have primary key defined.

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