适合不同相关实体处理一对多的模式 [英] Proper pattern to handle one-to-many with different related entities

问题描述

我有一个C＃项目，我使用实体框架作为ORM。我有一个用户，可以支付给许多银行。每个银行是一个单独的实体，每个银行都由不同的领域描述。

问题是 - 一个用户可以没有或许多不同 / code>秒。我不太确定如何建模 - 临时解决方案是添加一个额外的 UserBank 实体，与 1 。类似于（或多或少）类似于

  public class User 
 {
 public virtual UserBank银行{get;组; } 
 //（...）
} 
  

和

  public class UserBank 
 {
 public virtual User {get;组; } 
 public virtual Bank1 {get;组; } 
 public virtual Bank2 {get;组; } 
 public virtual Bank3 {get;组; } 
} 
  

在这种情况下，用户可能或可能没有任何银行中的帐户。如果他没有，值将为 NULL 。

这不完美 - 但至少用户不需要知道关于银行类型。问题是，如果我想添加一个新的银行，我需要修改 UserBank 实体，这违反了 O 在 SOLID 中，我试图一直遵循。

<另外，我不喜欢 UserBank 必须为N个银行存储N个空（NULL）列的想法，如果 User 没有任何银行账户。有没有适当的模式来处理这种情况？

---

编辑

我知道在原始SQL中这是一个比较容易的问题。这里的问题是如何使用实体框架进行代码优先。

解决方案

这看起来像一个古典的 m：n 关系。每个用户可以有不同的银行，每个银行将有很多用户。

您需要三个表：

• 用户（UserID，Name，...）


• 银行（BankID，Name，...）


• UserBank UserBankID，用户ID FK到用户，BankID FK到银行，更多细节...）

如果你想确保，用户不能与同一个银行拥有多个连接，您可以在UserID / BankID的组合上放置一个唯一的密钥，或者让它成为映射表的PK。但我不认为这是正确的...

实体表（User / Bank）持有他们的对象的描述，但没有更多。映射表获取描述这两者之间的连接的所有需要​​的数据（创建日期，活动的，帐户（应该是另一个实体表的FK等）...）

更新示例来说明一个 m：n -relationship

用户

  1 John 
 2 Jane 
 3 Tim 
  

银行

  1英格兰银行
 2德意志银行$ b 3碰撞& Desaster 
  

UserBank

 code> 1 1 1  - >用户1与Bank 1连接 - >约翰使用BoE 
 2 1 2  - >约翰也使用德意志银行也
 3 2 1  - >简在德意志银行
 4 3 3  - >而Tim位于C& D 
  

更新2

  public class User 
 {
 public int UserID {get; set} 
 public string Name ... 
 public List< UserBank> MyBanks {... fetch by this.UserID ...} 
} 
 public class Bank 
 {
 public int BankID {get; set} 
 public string Name {get; set;} 
 public List< UserBank> MyUsers {... fetch by this.BankID ...} 
} 
 
 public class UserBank 
 {
 public int UserBankID {get; set} 
 public User {get; set;} 
 public Bank {get; set;} 
} 
  

I have a C# project and I use Entity Framework as the ORM. I have a User, which is able to pay to many banks. Each bank is a separate entity and each one of them is described by different fields.

The problem is - one User can have no-or-many different Banks. I'm not really sure how to model this - the temporary solution was to add an additional UserBank entity, which is in 1:1 realtionship with User. The classes look (more or less) like that:

public class User
{
  public virtual UserBank Banks { get; set; }
  // (...)
}

and

public class UserBank
{
  public virtual User { get; set; }
  public virtual Bank1 { get; set; }
  public virtual Bank2 { get; set; }
  public virtual Bank3 { get; set; }
}

In that scenario, User may or may not have accounts in any of the Banks. If he doesn't have one, the value will be NULL.

It's not perfect - but at least User doesn't need to know anything about Bank types. The problem is that if I want to add a new Bank, I need to modify UserBank entity, which is violating the O in SOLID, which I try to always follow.

Additionally, I don't like the idea that UserBank has to store N empty (NULL) columns for N banks if User doesn't have any bank accounts. Is there a proper pattern to handle that situation?

---

EDIT

I am aware that it's a relatively easy problem in raw SQL. The problem here is how to do that with Entity Framework with code-first.

解决方案

This looks like a classical m:n relationship. Each User can have different banks and each bank will have many users.

You need three tables:

• User (UserID, Name, ...)
• Bank (BankID, Name, ...)
• UserBank(UserBankID, UserID FK-to-User, BankID FK-to-Bank, FurtherDetails ...)

If you want to ensure, that a user cannot have multiple connections with the same bank, you might place a unique key on the combination of UserID/BankID or let this be the PK of you mapping table. But I don't think this was correct actually...

The entity tables (User/Bank) hold a description of their object, but nothing more. The mapping table gets all the needed data which describes the connection between these two (date of creation, active, account (which should be a FK to another entity table) and so on...)

UPDATE example to illustrate a m:n-relationship

User

  1 John
  2 Jane
  3 Tim

Bank

 1 Bank of England
 2 Deutsche Bank
 3 Crash & Desaster

UserBank

 1 1 1 --> User 1 is connected with Bank 1 --> John uses BoE  
 2 1 2 --> John uses Deutsche Bank too  
 3 2 1 --> And Jane is at Deutsche Bank  
 4 3 3 --> while Tim is at C&D  

UPDATE 2

No experience with EF code first, but this would be the line in C#:

public class User
{
  public int UserID{get;set}
  public string Name...
  public List<UserBank> MyBanks{ ... fetch by this.UserID ... }
}
public class Bank
{
  public int BankID{get;set}
  public string Name{get;set;}
  public List<UserBank> MyUsers{... fetch by this.BankID ... }
}

public class UserBank
{
  public int UserBankID{get;set}
  public User{get;set;}
  public Bank{get;set;} 
}

这篇关于适合不同相关实体处理一对多的模式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！