C# EF代码优先-具有子实体的序列号

在Asp.NETWeb应用程序中使用EF6.X

考虑下面的父子关系。 订单实体可以有一个或多个订单行。 在OrderLine实体中，我希望有一个序列列

如上图所示，每个订单的顺序应从1开始。

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我如何通过EF实现这一点？需要一个简单的解决方案来解决此问题。

不可能自动执行此操作。订单行的数据模型将需要一个属性

SequenceNo

。更高级别的抽象必须确保每当添加“订单行”时，都会填充正确的

SequenceNo

public class Order
{
    // primary Key
    public int Id {get; set;}

    // an Order has a collection of OrderLines:
    public virtual ICollection<OrderLine> OrderLines {get; set;}
    ...
}

public class OrderLine
{
    public int Id {get; set;} // primary key

    // foreign key to owning Order
    public int OrderId {get; set;}
    public virtual Order Order {get; set;}

    public int OrderLineNo {get; set;}
    public int SequenceNo {get; set;}
    ...
}

public MyDbContrext : DbContext
{
    public DbSet<Order> Orders {get; set;}
    public DbSet<OrderLine> OrderLines {get; set;}
    ...
}

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您不能为每个订单行使用一个计数器吗？@Ephraim您能提供一个简单的代码示例吗？请解释这种关系。。。示例表做了一个垃圾工作，显示了什么与什么相关。这就是我想要的。谢谢！

public int IntroduceOrder(...)
{
    using (MyDbContext dbContext = ...)
    {
        Order orderToAdd = new Order()
        {
            ...
        }
        var addedOrder = dbContext.Orders.Add(orderToAdd);
        dbContext.SaveChanges();
        return addedOrder.Id;
    }
}

public OrderLine AddOrderLine(int orderId, ...)
{
    using (MyDbContext dbContext = ...)
    {
        // get the sequenceNo from the orderline of the order with orderId
        // with the highest sequenceNo
        // = first element when ordered descending
        int highestSeqenceNo = dbContext.OrderLines
            .Where(orderLine => orderLine.OrderId == orderId)
            .Select(orderLine => orderLine.SequenceNo)
            .OrderByDescending(sequenceNo => sequenceNo)
            .FirstOrDefault();
       // if there were no order lines yet, highestSequenceNo has value 0

       const int sequenceNoFirstOrderLine = 1;
       // or whatever value you want as sequenceNo for the first OrderLine

       int nextSequenceNo = (highestSequenceNo == 0) ? 
           sequenceNoFirstOrderLine :
           highestSequenceNo + 1;
       OrderLine orderLineToAdd = new OrderLine()
       {
           ...
           SequenceNo = nextSequenceNo,
       };
       var addedOrderLine = dbContext.Orders.Add(orderLineToAdd);
       dbContext.SaveChanges();
       return addedOrderLine;
    }
}