实体框架 4.1 代码 创建多对多关系的首选方法

我在Silverlight

应用程序中使用Silverlight 5 Beta SDK和EntityFramework 4.1。

我将尝试创建两个表"作者"和"书籍"。在SQL中，应该有第三个（连接）表，它使作者和书籍之间存在多对多关系（一个作者可以写很多本书，一本书可以由许多作者写）。

这是我到目前为止得到的：

namespace CodeFirst.Models.Web
{    
    public class Author
    {
        public Author()
        {
            this.Books = new HashSet<Book>();
        }
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        [Key]
        public int ID { get; set; }
        [Required]
        public string Name { get; set; }
        public ICollection<Book> Books { get; set; }
    }

    public class Book
    {
        public Book()
        {
            this.Authors = new HashSet<Author>();
        }

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        [Key]
        public int ID { get; set; }
        [Required]
        public string Name { get; set; }
        public ICollection<Author> Authors { get; set; }
    }

    // Should I do something like that:
    public class AuthorMapping : EntityTypeConfiguration<Author>
    {
        public AuthorMapping() : base()
        {   
            //this.HasMany (g => g.Books)
            //    .WithMany(m => m.Authors)
            //    .Map     (gm => gm.ToTable    ("Author_Book")
            //                      .MapLeftKey ("AuthorID")
            //                      .MapRightKey("BookID"));
        }
    }

    public class CodeFirstModelContext : DbContext
    {
        public CodeFirstModelContext() : base()
        {
            this.Database.Connection.ConnectionString = @".'MSSQLSERVER2008;Database=CodeFirst;Trusted_Connection=true;";
        }

        public DbSet<Author> Authors  { get; set; }
        public DbSet<Book>   Books { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.Add(new AuthorMapping());
            // tell Code First to ignore PluralizingTableName convention
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
        }
    }

    [EnableClientAccess()]
    public class CodeFirstDomainService : DomainService
    {
        public CodeFirstDomainService()
        {
            this.m_modelContext = new CodeFirstModelContext();
        }

        public IQueryable<Author> GetAuthors()
        {
            return this.m_modelContext.Authors;//.Include("Books");
        }
        public void InsertAuthor(Author Author)
        {
            this.m_modelContext.Insert(Author);
        }
        public void UpdateAuthor(Author Author)
        {
            this.m_modelContext.Update(Author, this.ChangeSet.GetOriginal(Author));
        }
        public void DeleteAuthor(Author Author)
        {
            this.m_modelContext.Delete(Author);
        }

        public IQueryable<Book> GetBooks()
        {
            return this.m_modelContext.Books;//.Include("Authors");
        }
        public void InsertBook(Book Author)
        {
            this.m_modelContext.Insert(Author);
        }
        public void UpdateBook(Book Author)
        {
            this.m_modelContext.Update(Author, this.ChangeSet.GetOriginal(Author));
        }
        public void DeleteBook(Book Author)
        {
            this.m_modelContext.Delete(Author);
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
                this.m_modelContext.Dispose();
            base.Dispose(disposing);
        }
        protected override bool PersistChangeSet()
        {
            this.m_modelContext.SaveChanges();
            return base.PersistChangeSet();
        }

        private CodeFirstModelContext m_modelContext;
    }
}

最明显的问题是，导航属性（作者中的书籍和书籍中的作者）不是从客户端项目中的代码设计器创建的。

我需要做什么？

编辑：好的，现在我只能同时使用其中一个导航属性。如果我尝试"包括"两者，则会收到以下错误：

Association 'Author_Book' defined on entity type 'CodeFirst.Models.Web.Author' is invalid. It is a foreign key association but the property type is not a singleton.

这是我更新的代码：

public class Author
{
    public Author()
    {
        this.Books = new Collection<Book>();
    }
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    public int ID { get; set; }
    [MaxLength(32)]
    [Required]
    public string Name { get; set; }
    [Association("Author_Book", "ID", "ID")]
    [Include]
    public Collection<Book> Books { get; set; }
}

public class Book
{
    public Book()
    {
        this.Authors = new Collection<Author>();
    }
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    public int ID { get; set; }
    [MaxLength(32)]
    [Required]
    public string Name { get; set; }
    [Association("Author_Book", "ID", "ID")]
    [Include]
    public Collection<Author> Authors { get; set; }
}

public class AuthorMapping : EntityTypeConfiguration<Author>
{
    public AuthorMapping() : base()
    {
        this.HasMany (g => g.Books)
            .WithMany(m => m.Authors)
            .Map     (gm => gm.ToTable("Author_Book"));
    }
}
public class BookMapping : EntityTypeConfiguration<Book>
{
    public BookMapping() : base()
    {
        this.HasMany (m => m.Authors)
            .WithMany(g => g.Books)
            .Map     (gm => gm.ToTable("Author_Book"));
    }
}

在我看来，实体框架仍然无法处理多对多关系。至少，这就是错误消息所暗示的。

编辑2：在 social.msdn 上阅读了这篇文章后，我更改了我的代码：

public class Author
{
    public Author()
    {
        this.Books = new Collection<Book>();
    }
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    public int ID { get; set; }
    [MaxLength(32)]
    [Required]
    public string Name { get; set; }
    [Association("Author_Book", "Book_ID", "Author_ID")]
    [Include]
    [ForeignKey("Book_ID")]
    public Collection<Book> Books { get; set; }
    public int Book_ID { get; set; }
}
public class Book
{
    public Book()
    {
        this.Authors = new Collection<Author>();
    }
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    public int ID { get; set; }
    [MaxLength(32)]
    [Required]
    public string Name { get; set; }
    [Association("Author_Book", "Author_ID", "Book_ID")]
    [Include]
    [ForeignKey("Author_ID")]
    public Collection<Author> Authors { get; set; }
    public int Author_ID { get; set; }
}

它没有解决我的问题。相同的错误仍然存在。我已经测试删除关联属性但没有成功。我在这里做错了什么吗？