Linq group by 带返回计数

Question

Net core and Linq. I have table like below

Orders Table

OrderId   Status
1         New
2         New
3         In Progress
4         In Progress
5         Closed
6         Closed

I have below model

public class SummaryEntity
 { 
  public int New { get; set; }
  public int InProgress { get; set; }
  public int Closed { get; set; }
 }

Then I need to return and bind to below model like below

New : 2
InProgress : 2
Closed : 2 

I have tried something like below

SummaryEntity result = (from item in Orders
                          group item by new { item.Status } into g
                          select new SummaryEntity{ //not sure how to get count and assign it to model }
                           );

I am finding hard to group by and assign values to model. Can someone help me to write query. Any help would be appreciated. Thank you

Answer 1

You've already grouped the items by status, so g.Key will contain the status value and g itself is an enumerable of the grouped items. If you want to calculate their count use Count() , eg:

var counts = from item in Orders
             group item by new { item.Status } into g
             select new {status=g.Key, count=g.Count()};

This will return one object per status value with its count. Getting different columns for each status is essentially pivoting, converting the rows to columns.

In this case though, where you know the status names in advance, you can convert the results into a dictionary and retrieve the counts by name, eg:

var dict=counts.ToDictionary(x=>x.status,x=>x.count);

var model= new SummaryEntity 
           {
               New        = dict.TryGetValue("New",out var c_n)
                            ? c_n : 0,
               InProgress = dict.TryGetValue("InProgress",out var c_p)
                            ? c_p : 0,
               Closed     = dict.TryGetValue("Closed",out var c_c)
                            ? c_c : 0,
           };

Dictionary.TryGetValue is used to avoid exceptions if a status value is missing

Answer 2

You model makes no sense. You have only status not New, InProgress, Closed. Try following:

            DataTable dt = new DataTable();
            dt.Columns.Add("OrderId", typeof(int));
            dt.Columns.Add("Status", typeof(string));
            
            dt.Rows.Add( new object[] { 1, "New"});
            dt.Rows.Add( new object[] { 2, "New"});
            dt.Rows.Add( new object[] { 3, "In Progress"});
            dt.Rows.Add( new object[] { 4, "In Progress"});
            dt.Rows.Add( new object[] { 5, "Closed"});
            dt.Rows.Add( new object[] { 6, "Closed"});

            var results = dt.AsEnumerable()
                .GroupBy(x => x.Field<string>("Status"))
                .Select(x => new { status = x.Key, count = x.Count() })
                .ToList();