Question

我正在尝试更新用户，因此我可以添加书（书名和作者），方法是简单地发送带有书的HTTP req的ID，然后进行搜索。我没有得到理想的结果，但是，一切似乎都正常，除了您可以从下面的图片中看到的那样，我得到的是书中的所有内容（包括标题和作者）都为空值，而我搜索时不是如图2所示。

    // Update user to include a rented book
    public Users Update(Users user)
    {
        var usr = ctx.User
            .Include(s => s.BooksRented)
             .FirstOrDefault(b => b.Id == user.Id);

        foreach (var bar in user.BooksRented)
        {
            var book = ctx.Book
                .FirstOrDefault(b => b.Id == bar.Id);

            //book.CurrentUser = usr;
            book.UserId = user.Id;
            usr.BooksRented.Add(book);

            //ctx.Entry(book).State = EntityState.Modified;
        }

        //ctx.Entry(usr).State = EntityState.Modified;
        ctx.SaveChanges();
        return usr;
    }

    // Also tried this as suggested, it loops through by adding the user to 
    //  books back and forth until it throws an error.
    public Users Update(Users user)
    {
        Books book = new Books();
        var r = ctx.User
            .FirstOrDefault(b => b.Id == user.Id);

        ctx.Entry(r).State = EntityState.Modified;

        foreach (var bar in user.BooksRented)
        {
            book = ctx.Book
                .FirstOrDefault(b => b.Id == bar.Id);
            book.UserId = user.Id;
            ctx.Entry(book).State = EntityState.Modified;
        }


        ctx.SaveChanges();
        return r;
    }

public class Books
{
    public int Id { get; set; }
    public string BookTitle { get; set; }
    public string Author { get; set; }
    public bool InRent { get; set; }
    public Users CurrentUser { get; set; }
    public DateTime Released { get; set; }
    public DateTime RentedDate { get; set; }
    public int UserId { get; set; }
}

public class Users
{
    public int Id { get; set; }
    public string Surname { get; set; }
    public string Lastname { get; set; }
    public List<Books> BooksRented { get; set; }
}

 protected override void OnModelCreating(ModelBuilder modelBuilder)
 {
     base.OnModelCreating(modelBuilder);

     modelBuilder.Entity<Users>()
            .HasMany(a => a.BooksRented)
            .WithOne(r => r.CurrentUser)
            .HasForeignKey(f => f.UserId);

 }

Answer 1

1）如果是EF，则需要在书本中使用外键UserId

2）您返回自己发送给该方法的用户

3）这是什么？您从数据库中保存了从数据库中收到的相同对象

 Books book = new Books();
        foreach (var bar in user.BooksRented)
        {
            book = ctx.Book
                .FirstOrDefault(b => b.Id == bar.Id);
        }
        ctx.Entry(book).State = EntityState.Modified;

我想它可以用这样的东西：

1）在书籍中添加UserId

    public class Books
{
    public int Id { get; set; }
    public string BookTitle { get; set; }
    public string Author { get; set; }
    public bool InRent { get; set; }
    public Users CurrentUser { get; set; }
    public DateTime Released { get; set; }
    public DateTime RentedDate { get; set; }

    public int UserId {get; set;]
}

2）将主代码更改为：

   public Users RentBook(Users user)
{
    var r = ctx.User
        .FirstOrDefault(b => b.Id == user.Id); 

    ctx.Entry(user).State = EntityState.Modified;

    foreach (var bar in user.BooksRented)
    {
        book = ctx.Book
            .FirstOrDefault(b => b.Id == bar.Id);
        book.UserId = user.Id;
        ctx.Entry(book).State = EntityState.Modified;
    }


    ctx.SaveChanges();
    return r.Include(x => x.BooksRented);
}

这也不是完全理想的，但我认为它会起作用。唯一不确定的是最后一行。

通过搜索ID在EF中一对多更新

1 个答案: