[英]Linq GroupBy with sort, take first, and return a list
我陷入了Linq-to-SQL查詢。 我有一個項目表,每個用戶有多個項目。 我想獲取每個用戶所有最新項目的列表。 這就是我所擁有的:
var TheList = (from t in MyDataContext.TheTable
where t.SomeDate > DateTime.UtcNow.AddMonths(-3)
group t by t.UserID into TheUserGroups
from g in TheGroups
orderby g.SomeDate descending
select new SomeObject()
{
TheUserID = g.UserID,
.....
}).ToList();
問題在於它返回的是每個用戶的所有項目,而不是每個用戶的最新元素。 我需要更改什么才能獲得預期的結果?
嘗試以下操作:
var TheList = (from t in MyDataContext.TheTable
where t.SomeDate > DateTime.UtcNow.AddMonths(-3)
orderby g.SomeDate descending
select new SomeObject()
{
TheUserID = g.UserID,
})
.GroupBy(x => x.TheUserID)
.Select(x => x.FirstOrDefault())
.ToList();
如果我正確理解您的意見:
public class Order
{
public int OrderId { get; set; }
public int UserId { get; set; }
public DateTime Date { get; set; }
public string ItemName { get; set; }
}
table.Where(o => o.Date < DateTime.UtcNow.AddMonths(-3))
.GroupBy(o => o.UserId)
.Select(g => new { UserId = g.Key, LastOrder = g.OrderByDescending(o => o.Date).FirstOrDefault() })
.ToList();
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