在 LINQ C# 中按日期分组

Question

>我正在尝试在 LINQ 查询中按日期分组并显示如下所示的输出

startdates: [
startdate: “4/1/2014”,
users: [
{userId, …},
{userId, …}
],
startdate: “4/2/2014”, users: [
{userId, …}
],
 …
]

代码如下所示

db.Users
    .Where(x => (x.startDate >= startDate) && (x.startDate <= endDate))
    .GroupBy(x => new { x.startDate.Day, x.startDate.Month, x.startDate.Year })                    
    .ToList()
    .Select(y => new 
    {
    startdates = y.Select(k => 
    new {startdate = (k.startDate.Month.ToString() + "/" + k.startDate.Day.ToString() + "/" + k.startDate.Year.ToString()), 
    users = y.Select(z => 
    new {userId = z.userId,
    userName = z.userName})})});

即使"用户"按"开始日期

"分组，输出包含的"开始日期"的次数也是"用户数"的多次。输出如下所示。我试着把.Distinct（） 但它仍然重复开始日期。有人可以帮忙吗？

[{"startdates":
[{"startdate":"04/01/2014",
"users":[
{"userId":1},"userName":"John"}
{"userId":2},"userName":"Mike"}],
[{"startdate":"04/01/2014",
"users":[
{"userId":1},"userName":"John"}
{"userId":2},"userName":"Mike"}],
[{"startdate":"04/02/2014",
"users":[
{"userId":3},"userName":"AL"}
{"userId":4},"userName":"Test"}],
[{"startdate":"04/02/2014",
"users":[
{"userId":3},"userName":"AL"}
{"userId":4},"userName":"Test"}]

Answer 1

问题是你的选择部分，在这里：

.Select(y => new 
{
startdates = y.Select(k => 
new {startdate = (k.startDate.Month.ToString() + "/" + k.startDate.Day.ToString() + "/" + k.startDate.Year.ToString()), 
users = y.Select(z => 
new {userId = z.userId,
userName = z.userName})})});

你在那里筑巢太多了。您正在为组中的每个元素创建一个startdate部件。

目前还不清楚您为什么要按三个单独的部分进行分组，但我怀疑这会满足您的需求：

db.Users
  .Where(x => (x.startDate >= startDate) && (x.startDate <= endDate))
  .GroupBy(x => x.startDate.Date) // Or just x.startDate 
  .AsEnumerable() // Do the rest of the query locally
  .Select(group => new 
  {
      startdate = group.Key.ToString("MM/dd/yyyy"),
      users = group.Select(z => new { z.userId, z.userName })
  });

如果需要将其包装在startdates字段中，则可以使用：

var result = new { startdates = query.ToArray() };