实体框架4.1代码优先 - 仅使用数据注释来定义多对多 [英] Entity Framework 4.1 Code First - Define many-to-many using data annotations only

问题描述

是否可以在Entity Framework 4.1（Code First方法）中使用Data Annotations定义多对多关系，而不使用模型构建器？

例如，如：

  Product = {Id，Name，...} 
 Category = {Id，Name， ...} 
 ProductCategory = {ProductId，CategoryId} 
  

你得到的照片。 / p>

我不想在上下文中有两个多对一的中间实体 ProductCategory ，因为我没有任何额外的数据，只有两个FK。此外，我应该能够定义中间表的表名，以便与现有数据库一起使用。

解决方案

可以使用默认约定或数据注释定义多对多，但是不可以在没有模型构建器的情况下更改映射到连接表（表的名称和列）。简单的多对多：

  public class Product 
 {
 public int Id {get;组; } 
 public virtual ICollection< Category>分类{get;组; 
} 
 
 public class Category 
 {
 public int Id {get;组; } 
 public virtual ICollection< Product>产品{get;组; 
} 
  

对于使用注释，您可以使用：

  public class Product 
 {
 [Key] 
 public int Id {get;组; } 
 [InverseProperty（Products）] 
 public virtual ICollection< Category>分类{get;组; 
} 
 
 public class Category 
 {
 [Key] 
 public int Id {get;组; } 
 [InverseProperty（Categories）] 
 public virtual ICollection< Product>产品{get;组; } 
} 
  

如果需要控制连接表到现有数据库的映射， code>模型构建器。数据注释不如流畅的API强大。

Is it possible to define a many-to-many relationship in Entity Framework 4.1 (Code First approach) using Data Annotations only, without model builder?

For example, something like:

Product = { Id, Name, ... }
Category = { Id, Name, ... }
ProductCategory = { ProductId, CategoryId }

You get the picture.

I don't want to have an intermediate entity ProductCategory in the context with two many-to-ones since I don't have any additional data, just the two FKs. Also, I should be able to define table name for the intermediate table for use with an existing database.

解决方案

It is possible to define many-to-many with default conventions or with data annotations but it is not possible to change mapping to junction table (table's name and columns) without model builder. Simple many-to-many:

public class Product
{
    public int Id { get; set; }
    public virtual ICollection<Category> Categories { get; set; }
}

public class Category
{
    public int Id { get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

For using annotations you can use:

public class Product
{
    [Key]
    public int Id { get; set; }
    [InverseProperty("Products")]
    public virtual ICollection<Category> Categories { get; set; }
}

public class Category
{
    [Key] 
    public int Id { get; set; }
    [InverseProperty("Categories")]
    public virtual ICollection<Product> Products { get; set; }
}

If you need to control mapping of junction table to existing database you need modelBuilder. Data annotations are not as powerful as fluent API.

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