C# EntityFramework 加入

Question

我想根据数量加入 2 个实体的结果。这就是我所拥有的...

订单 #1

OrderID    CustomerID    ItemID    Description    POS#    Cost    Quantity
1          1             1         Apples         111     1.25    3
1          1             2         Oranges        222     1.12    5
1          1             3         Bananas        333     1.17    5

订单 #2

OrderID    CustomerID    ItemID    Description    POS#    Cost    Quantity
2          1             1         Apples         111     1.25    7
2          1             2         Oranges        222     1.12    2
2          1             3         Bananas        333     1.17    5

这是我用来获取每张票的代码：

public OrderEntity getOrder(int orderId)
{
    var data = from c in Orders
               where c.OrderID == orderId
               select c;
    return data;
}

我将如何编写 LINQ 代码来组合 2 张票以便得到数量总和？它应该看起来像这样...

订购门票 #1 和 #2

CustomerID    ItemID    Description    POS#    Cost    Quantity
1             1         Apples         111     1.25    10
1             2         Oranges        222     1.12    7
1             3         Bananas        333     1.17    10

看来我应该可以做这样的事情...

public List<OrderEntity> getCustomerOrders(int customerId)
{
    var data = from c in Orders
               where c.CustomerID == customerId
               select c;
    return data.ToList();
}

问题是我无法弄清楚分组。那里有很多关于如何编写用于分组的 EF 代码的信息，但我不确定我是否应该按 CustomerID 或数量进行分组。非常感谢任何有关如何在此处进行分组的提示。

Answer 1

您应该按 CustomerID 和 ItemID 分组：

尝试这样的事情：

public List<OrderEntity> getCustomerOrders(int customerId)
{
    var data = from c in Orders
               where c.CustomerID == customerId
               group c by new { c.CustomerID, c.ItemID } into g
               select new OrderEntity () {
                  CustomerID = g.Key.CustomerID,
                  ItemID =  g.Key.ItemID,
                  Quantity = g.Sum(x => x.Quantity) 
               };
    return data.ToList();
}

我不确定您是如何定义数据的，但是如果您需要在结果中包含 Description POS、Cost，请尝试：

public List<OrderEntity> getCustomerOrders(int customerId)
    {
        var data = from c in Orders
                   where c.CustomerID == customerId
                   group c by new { c.CustomerID, c.ItemID,c.Description,c.POST,c.Cost } into g
                   select new OrderEntity () {
                      CustomerID = g.Key.CustomerID,
                      ItemID =  g.Key.ItemID,
                      Quantity = g.Sum(x => x.Quantity),
                      Description = g.Key.Description,
                      POST = g.Key.POST,
                      Cost = g.Key.Cost 
                   };
        return data.ToList();
    }

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