Question

I have those maps in my repository.

public IQueryable<AwType> GetAwTypes() {     return from awt in _db.AwTypes            select new AwType            {                Id = awt.Id,                Header = awt.Header,                Description = awt.Description            }; }  public IQueryable<Aw> GetAws() {     return from aw in _db.Aws            select new Aw            {                Id = aw.Id,                Bw = (from bw in GetBws()                           where bw.Id == aw.Bw                              select bw                          ).SingleOrDefault(),                AwType = (from awt in GetAwTypes()                             where awt.Id == awAwType                             select awt                         ).SingleOrDefault(),                AwAttribute = aw.AwAttribute            }; } 

In service I want to get count of Bws grouped by AwType as List<KeyValuePair<AwType, int>>. When I call that linq query :

var awGroups = from aw in _repository.GetAws() group aw by aw.AwType into newGroup select newGroup;  List<KeyValuePair<AwType, int>> RetGroups = new List<KeyValuePair<AwType, int>>(); foreach (var group in awGroups) {     RetGroups.Add(new KeyValuePair<AwType, int>(group.Key, group.Count())); } return RetGroups; 

I get an error that is saying I can’t group by on an object I have to group by a scalar value like aw.AwType.Id.

Is there a way to get ‘AwType, int’ pairs in one call?

Answer 1

AwType is a reference type. It would be a bad idea to group on that reference type… Each AwType in that query is a unique reference, so n elements would yield n groups.

Try this:

var awGroups = from aw in _repository.GetAws() group aw by aw.AwType.ID into newGroup  //changed to group on ID select newGroup;  List<KeyValuePair<AwType, int>> RetGroups = new List<KeyValuePair<AwType, int>>(); foreach (var group in awGroups) {     //changed to get the first element of the group and examine its AwType     RetGroups.Add(new KeyValuePair<AwType, int>(group.First().AwType, group.Count())); } return RetGroups;