c# - 首先编码与关系表中属性的多对多关系

Question

我想用关系表创建关系属性。下面是引用代码。但代码创建了 2 个表 BookStudents 和 BookStudents1。其中一个具有没有外键的关系属性，另一个创建没有属性但具有外键的表。我该如何解决这个问题？

public class BookStudent
{
    [Key, Column(Order = 0)]
    public int BookID { get; set; }
    [Key, Column(Order = 1)]
    public int StudentID { get; set; }
    public DateTime FromDate { get; set; }
    public DateTime ToDate { get; set; }
}


public class Context : DbContext
{
    public Context() : base("name=DefaultConnection") { }
    public DbSet<Book> Books { get; set; }
    public DbSet<Student> Students { get; set; }
    public DbSet<BookStudent> BookStudents { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Book>().HasMany<Student>(t => t.Students).WithMany(t => t.Books).Map(t =>
        {
            t.MapLeftKey("BookId");
            t.MapRightKey("StudentId");
            t.ToTable("BookStudents");
        });
    }
}

Answer 1

在代码优先中，很多情况下我们不需要在 OnModelCreating 上显式定义关系。使用下面的代码这将解决您的问题。

public class BookStudent
{
    [Key, Column(Order = 0)]
    public int BookID { get; set; }
    [Key, Column(Order = 1)]
    public int StudentID { get; set; }
    public DateTime FromDate { get; set; }
    public DateTime ToDate { get; set; }

    //below two lines will define foreign key
    public Student Student { get; set; }
    public Book Book { get; set; }
}


public class Context : DbContext
{
    public Context() : base("name=DefaultConnection") { }
    public DbSet<Book> Books { get; set; }
    public DbSet<Student> Students { get; set; }
    public DbSet<BookStudent> BookStudents { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        //remove below code
        //modelBuilder.Entity<Book>().HasMany<Student>(t => t.Students).WithMany(t => t.Books).Map(t =>
        //{
        //    t.MapLeftKey("BookId");
        //    t.MapRightKey("StudentId");
        //    t.ToTable("BookStudents");
        //});
    }
}