C# LINQ Select JOIN GroupBy 不工作

Question

I am using entityFramework Core and got a LINQ query select, inner join, where and got the results. I need to add GroupBy and it an error. I followed a few posts and mimic their code but I have been stucked.

I am having issue with translating to LINQ

Here is my linq that is working without the GroupBy

var result = this.myDbContent.Table1
               .Join(this.Table2,
                     table1 => table1.myId,
                     table2 => table2.myId,
                     (table1 ,table2) => {table1 ,table2}
               )
               .Join(this.Table3,
                     table1_table2 => table1_table2.table1.myId,
                     table3 => table3.myId,
                     (table1_table2 ,table3) => {tabtable1_table2 e1 ,table3}
               )
               .Where(
                 s => s.table1_table2.table1.myId == 1 &&
                 s.table1_table2.table2.isCompleted == true
               )
               .Select(s => new
               {
                  MyID = s.table1_table2.table1.myId,
                  MyDate = s.table1_table2.Table2.CompletedDate
               });

This query works and returns records

In the following I added the GroupBy according to another post

var result = this.myDbContent.Table1
               .Join(this.Table2,
                     table1 => table1.myId,
                     table2 => table2.myId,
                     (table1 ,table2) => {table1 ,table2}
               )
               .Join(this.Table3,
                     table1_table2 => table1_table2.table1.myId,
                     table3 => table3.myId,
                     (table1_table2 ,table3) => {tabtable1_table2 e1 ,table3}
               )
               .Where(
                 s => s.table1_table2.table1.myId == 1 &&
                 s.table1_table2.table2.isCompleted == true
               )
               .GroupBy(s => new
                 {
                    MyID = s.table1_table2.table1.myId,
                    MyDate = s.table1_table2.Table2.CompletedDate
                 }
               )
               .Select(s => new
               {
                  MyID = s.Key.myId,
                  MyDate = s.Key.CompletedDate,
                  Count = s.Count()
               });

When I run this query with the GroupBy, I get an"SYstem.InvalidOperationException

I am trying to add the following SELECT GROUPBY to the working QUERY

Select Count(*) AS Counts, MyID, MYDATE
FROM ( the working query above )
GROUP BY MyID, MYDATE

Thanks

Answer 1

Yourgroup key only has MyID and MyDate fields - the references to the joined tables are gone, so reference those in your select:

.Select(s => new
           {
              MyID = s.Key.MyID,
              MyDate = s.Key.MyDate,
              Count = s.Count()
           }

Answer 2

Convert it to a list or Enumerable before grouping

var result = this.myDbContent.Table1
               .Join(this.Table2,
                     table1 => table1.myId,
                     table2 => table2.myId,
                     (table1 ,table2) => {table1 ,table2}
               )
               .Join(this.Table3,
                     table1_table2 => table1_table2.table1.myId,
                     table3 => table3.myId,
                     (table1_table2 ,table3) => {tabtable1_table2 e1 ,table3}
               )
               .Where(
                 s => s.table1_table2.table1.myId == 1 &&
                 s.table1_table2.table2.isCompleted == true
               ).AsEnumerable()
               .GroupBy(s => new
                 {
                    MyID = s.table1_table2.table1.myId,
                    MyDate = s.table1_table2.Table2.CompletedDate
                 }
               )
               .Select(s => new
               {
                  MyID = s.Key.table1_table2.table1.myId,
                  MyDate = s.Key.table1_table2.Table2.CompletedDate,
                  Count = s.Count()
               });