Question

我有两个具有多对多关系的对象：

public class Order
{
   public int OrderID { get; set; }
   public string OrderName { get; set; }
   public virtual Collection<Product> Products { get; set; } = new Collection<Product>();
}

public class Product
{
   public int ProductID { get; set; }
   public string ProductName { get; set; }
   public int OrderID { get; set; }
   public virtual Collection<Order> Orders { get; set; } = new Collection<Order>();
}

// Mapping table
public class OrderProduct
{
   public int OrderId { get; set; }
   public Order Order { get; set; }
   public int ProductId { get; set; }
   public Product Product { get; set; }
}

我想向数据库中添加一个包含现有产品集合的新订单（我的API将有一个ProductID数组输入），所以我的执行方式如下：

private void AddOrder(int[] productIDs)
{
    Order newOrder = new Order();
    newOrder.Name = "New Order";

    // Here I have no clue which would be the correct way...Should I do 
    // Approach A(fetch each related entity - Product from database then add them into the collection of my new base entity - Order):
    productIDs.ToList().Foreach(p => 
        {
            newOrder.Products.Add(_dbContext.Product.FindById(p))
        }
    );

    _dbContext.Orders.Add(newOrder);
    var newOrderID = _dbContext.SaveChanges();

    // then fetch each product from database and add my new Order to its collection and save
    productIDs.ToList().Foreach(p => 
        {
            var existedProductFromDb = _dbContext.Product.FindById(p)；
            existedProductFromDb.Orders.Add(newOrder);
            _dbContext.SaveChanges();
        }
    );
}

我真的需要在Entity Framework Core中订购和产品之间的映射表吗？否则，应对上述情况的正确方法是什么？

Answer 1

您的实体使用联接表不表示多对多关系。实际上，您根本不使用联接表。

因此，请先修复您的实体：

public class Order
{
   public int OrderID {get;set;}
   public string OrderName {get;set;}

   public ICollection<OrderProduct> Products { get; set; } = new HashSet<OrderProduct>();
}

public class Product
{
   public int ProductID {get;set;}
   public string ProductName {get;set;}

   public ICollection<OrderProduct> Orders { get; set; } = new HashSet<OrderProduct>();
}

包含许多Order的新Product就像新OrderProduct的集合一样简单：

private void AddOrder(int[] productIDs)
{
    Order newOrder = new Order();
    newOrder.Name = "New Order";

    foreach (int productId in productIDs)
    {
        newOrder.Products.Add(new OrderProduct { ProductId = productId });
    }

    _dbContext.Orders.Add(newOrder);
    _dbContext.SaveChanges();
}

还要注意，SaveChanges返回数据库中受影响的行数，而不是插入项的ID。

插入具有数据库中存在的许多相关实体的实体

1 个答案: