如何使用结果映射将小巧的结果转换为字典

Question

我想使用此处表示的 splitOn 功能：https://dapper-tutorial.net/result-multi-mapping

将结果的每个 Order 分组为一个整数属性 "EmployeeId"。我听从了 How to map to a Dictionary object from database results using Dapper Dot Net?

的建议

但是我得到了一个 An item with the same key has already been added. 那么我怎样才能按 EmployeeId 对我的订单进行分组？

我无法修改 Order class 并且我更喜欢使用字典而不是创建包装 Order 的 class。但是，如果没有其他方法，我愿意接受包装 Order

的想法

https://dotnetfiddle.net/hn6Sjf

public class Program
{
    public class Order
    {
        public int OrderID { get; set; }
        public int CustomerID { get; set; }
        public DateTime OrderDate  { get; set; }
        public int ShipperID  { get; set; }
    }

    public static void Main()
    {
        string sql = @"
            SELECT TOP 10
                EmployeeID,
                OrderID,
                CustomerID,
                OrderDate,
                ShipperID
            FROM Orders 
            ORDER BY OrderID;
        ";

        using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
        {           
            var rawList = connection.Query<Order>(sql);
            FiddleHelper.WriteTable(rawList);   


                var dict = connection.Query<int, List<Order>, KeyValuePair<int, List<Order>>>(sql,
                    (s, i) => new KeyValuePair<int, List<Order>>(s, i), null, null, true, "OrderID")
                    .ToDictionary(kv => kv.Key, kv => kv.Value);

            FiddleHelper.WriteTable(dict);              
        }
    }
}

Answer 1

您可以创建一个信封 class（如果您愿意，也可以使用动态）：

public class OrderEntity
{
  public int EmployeeID {get;set;}
  public Order Order {get;set;}
}

然后直接从结果集映射到按员工 ID 分组的字典：

var dict = new Dictionary<int,List<Order>>();
var r = connection.Query<OrderEntity, Order, OrderEntity>(sql,(orderEntity, order) => 
    {
        // You can skip that line if you want, the orderEntity is (probably) never used.
        orderEntity.Order = order;

        if(dict.ContainsKey(orderEntity.EmployeeID))
        {
            dict[orderEntity.EmployeeID].Add(orderEntity.Order);
        }
        else
        {
            dict.Add(orderEntity.EmployeeID, new List<Order> {orderEntity.Order});
        }

        return orderEntity;
    }, splitOn: "OrderID");

此方法在结果集的 1 次迭代中完成所有操作，并且只需要 O(1) 键查找字典。

Answer 2

这能满足您的需求吗？

var dict = connection.Query<int, Order, ValueTuple<int, Order>>(sql,
        (s, i) => ValueTuple.Create(s, i), null, null, true, "OrderID")
        .GroupBy(t => t.Item1, t => t.Item2, (k, v) => new {Key = k, List = v})
        .ToDictionary(kv => kv.Key, kv => kv.List);

Fiddle

如何使用结果映射将小巧的结果转换为字典

How to turn dapper result into a dictionary using result mapping

c#

sql-server

dictionary

dapper