c# - Entity Framework 4.1 InverseProperty 属性

Question

只是想了解更多关于 RelatedTo 属性的信息，我发现它已被 EF 4.1 RC 中的 ForeignKey 和 InverseProperty 属性所取代。

有谁知道有关此属性变得有用的场景的任何有用资源？

我应该在导航属性上使用这个属性吗？示例:

public class Book
{
  public int ID {get; set;}
  public string Title {get; set;}

  [ForeignKey("FK_AuthorID")]
  public Author Author {get; set;}
}  

public class Author
{
  public int ID {get; set;}
  public string Name {get; set;}
  // Should I use InverseProperty on the following property?
  public virtual ICollection<Book> Books {get; set;}
}

Answer 1

我为 InversePropertyAttribute 添加了一个示例。它不仅可以用于自引用实体中的关系(如 Ladislav 的回答中链接的示例)，还可以用于不同实体之间关系的“正常”情况:

public class Book
{
    public int ID {get; set;}
    public string Title {get; set;}

    [InverseProperty("Books")]
    public Author Author {get; set;}
}

public class Author
{
    public int ID {get; set;}
    public string Name {get; set;}

    [InverseProperty("Author")]
    public virtual ICollection<Book> Books {get; set;}
}

这将描述与 Fluent Code 相同的关系:

modelBuilder.Entity<Book>()
            .HasOptional(b => b.Author)
            .WithMany(a => a.Books);

……或者……

modelBuilder.Entity<Author>()
            .HasMany(a => a.Books)
            .WithOptional(b => b.Author);

现在，在上面的示例中添加 InverseProperty 属性是多余的:映射约定无论如何都会创建相同的单一关系。

但是考虑这个例子(图书馆只包含两位作者合着的书):

public class Book
{
    public int ID {get; set;}
    public string Title {get; set;}

    public Author FirstAuthor {get; set;}
    public Author SecondAuthor {get; set;}
}

public class Author
{
    public int ID {get; set;}
    public string Name {get; set;}

    public virtual ICollection<Book> BooksAsFirstAuthor {get; set;}
    public virtual ICollection<Book> BooksAsSecondAuthor {get; set;}
}

映射约定不会检测这些关系的哪一端属于一起并实际创建四个关系(在 Books 表中有四个外键)。在这种情况下，使用 InverseProperty 将有助于在我们的模型中定义我们想要的正确关系:

public class Book
{
    public int ID {get; set;}
    public string Title {get; set;}

    [InverseProperty("BooksAsFirstAuthor")]
    public Author FirstAuthor {get; set;}
    [InverseProperty("BooksAsSecondAuthor")]
    public Author SecondAuthor {get; set;}
}

public class Author
{
    public int ID {get; set;}
    public string Name {get; set;}

    [InverseProperty("FirstAuthor")]
    public virtual ICollection<Book> BooksAsFirstAuthor {get; set;}
    [InverseProperty("SecondAuthor")]
    public virtual ICollection<Book> BooksAsSecondAuthor {get; set;}
}

这里我们只会得到两个关系。 (注意:InverseProperty 属性仅在关系的一端是必需的，我们可以省略另一端的属性。)