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EF代码优先-具有子实体的序列号

[英]EF Code First - Having Sequence Number for child entities

Using EF 6.X with Asp.Net web application. 将EF 6.X与Asp.Net Web应用程序一起使用。

Consider below parent child relationship. 考虑以下亲子关系。 A Order Entity can have one or more OrderLines. 订单实体可以具有一个或多个订单行。 In the OrderLine entity I would like to have a sequence column. 在OrderLine实体中,我想要一个序列列。

在此处输入图片说明

As shown in the above image, the sequence should be start from 1 for each Orders. 如上图所示,每个订单的顺序应从1开始。 How can I achieve this through EF? 如何通过EF实现这一目标? Expecting a simple solution to solve this. 期待一个简单的解决方案来解决这个问题。

It is not possible to do this automatically. 无法自动执行此操作。 Your data model of the order line will need a property SequenceNo . 您的订单行数据模型将需要属性SequenceNo Higher levels of abstraction Data Access Layer? 更高级别的抽象数据访问层? will have to make sure that whenever an 'OrderLine' is added the correct SequenceNo is filled. 必须确保无论何时添加“ OrderLine”,都必须填写正确的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;}
    ...
}

Higher Level Of abstraction 更高的抽象水平

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;
    }
}

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