IList GroupBy question

Question

User-492280791 posted

Hi All,

GroupBy returns an IGrouping< MyClass >

var groupdResult = result.GroupBy(x => x.MyField).ToList();

How to avoid this error:

Error 1 Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Collections.Generic.IList<ccc.Ets.Entities.ErrorMessageGroup>'. An explicit conversion exists (are you missing a cast?)

Thanks!

Answer 1

User-271186128 posted

Hi SpongeBert,

According to your code and description, I create a sample using the following code. They all worked well on my side. Please refer to them:

            using (MyTestDBEntities context = new MyTestDBEntities())
            {
               var query3 = customer.GroupBy(cc => cc.EmployeeID).ToList();
                GridView2.DataSource = query3;
                GridView2.DataBind();
            }

and

                List<StudentClass> list = new List<StudentClass>();
                for (int i = 1; i <= 5; i++)
                {
                    StudentClass stu = new StudentClass();
                    stu.StuID = i;
                    stu.StuName = "AAA" + i.ToString();
                    list.Add(stu);
                }

                var query4 = list.GroupBy(cc => cc.StuID).ToList();


                GridView2.DataSource = query4;
                GridView2.DataBind();

They all display the key value, and didn't meet any error. So, I suppose perhaps the issue, is related to the result, I suggest you check it. If possible you could post more details information about the result.

Best regards,
Dillion

Answer 2

User-492280791 posted

Hi Dillion,

Thanks for your reply. Can you do another test with IList instead of List? IList<StudentClass> list = new IList<StudentClass>();

In my test scenario I tried like this:

            IList<ErrorMessageGroup> finalList2 = new List<ErrorMessageGroup>();
            return finalList2.GroupBy(x => x.GroupingCriterion1Value); 

but I get following error:

Error 2 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Linq.IGrouping<string,Ccc.Eee.Entities.ErrorMessageGroup>>' to 'System.Collections.Generic.IList<Ccc.Eee.Entities.ErrorMessageGroup>'. An explicit conversion exists (are you missing a cast?) 

Regards,

B

Answer 3

User-271186128 posted

Hi SpongeBert,

Can you do another test with IList instead of List? IList<StudentClass> list = new IList<StudentClass>();

In my test scenario I tried like this:

            IList<ErrorMessageGroup> finalList2 = new List<ErrorMessageGroup>();
            return finalList2.GroupBy(x => x.GroupingCriterion1Value); 

Please try to use the following code:

         IList<ErrorMessageGroup> finalList2 = new List<ErrorMessageGroup>();
            return finalList2.GroupBy(x => x.GroupingCriterion1Value).Select(g => g.First()).ToList(); 

Best regards,
Dillion