.Join .Group Lambda multiple table - asp.net-mvc

Question

I need to convert:
SELECT Author.AuthorName, Author.AuthorSurname , Category.CategoryName, COUNT(Record.IdCategory) AS Ilosc
FROM ((Record
INNER JOIN Author ON Author.Id = Record.IdAuthor)
INNER JOIN Category ON Category.Id = Record.IdCategory)
GROUP BY AuthorName, AuthorSurname, CategoryName
Order by Ilosc ASC
To lambda.
I have created
public class SortModel
{
public string Imie { get; set; }
public string Nazwisko { get; set; }
public string Kategoria { get; set; }
}
For now i wrote this code but i need to add .groupby:
public List<SortModel> GetAuthorCategories()
{
var context = new KolekcjaPlytEntities2();
List<SortModel> queryAllCustomers = context.Record
.Join( context.Author, r => r.IdAuthor, a => a.Id, (r, a) => new {r, a})
.Join(context.Category, c => c.r.IdCategory, cn => cn.Id, (c, cn) => new SortModel()
{
Imie = c.a.AuthorName,
Nazwisko = c.a.AuthorSurname,
Kategoria = cn.CategoryName,
})
.ToList();
return queryAllCustomers;
}
Thanks.

Answer 1

You could use LINQ query expression like this one.
List<SortModel> queryAllCustomers = (from r in context.Record
join a in context.Author on r.IdAuthor equals a.Id
join c in context.Category on r.IdCategory equals c.Id
group new {a, c} by new {a.AuthorName, a.AuthorSurname , c.CategoryName} into gruopAC
let countCategory= gruopAC.Count()
orderby countCategory
select new SortModel
{
Imie=gruopAC.Key.AuthorName,
Nazwisko =gruopAC.Key.AuthorSurname ,
Kategoria =gruopAC.Key.CategoryName,
Ilosc=countCategory}).ToList()

Answer 2

Suppose you have
public class SortModel
{
public string Imie { get; set; }
public string Nazwisko { get; set; }
public string Kategoria { get; set; }
public int Ilosc { get; set; }
}
You can try this code:
public List<SortModel> GetAuthorCategories()
{
var context = new KolekcjaPlytEntities2();
List<SortModel> queryAllCustomers = context.Record
.Join(context.Author, r => r.IdAuthor, a => a.Id, (r, a) => new {r, a})
.Join(context.Category, ar => ar.r.IdCategory, c => c.Id, (ar, c) => new {
r = ar.r,
a = ar.a,
c = c
})
// Here you have a IEnumerable<dynamic> of items { a = Author, c = Category, r = Record }
// All items with same { a.Id, c.Id } are grouped
.GroupBy(x => new { x.a.Id, x.c.Id }, (x, items) => new SortModel()
{
// First() cannot return null, we have inner join everywhere
Imie = items.First().a.AuthorName,
Nazwisko = items.First().a.AuthorSurname,
Kategoria = items.First().c.CategoryName,
Ilosc = items.Count()
})
.ToList();
return queryAllCustomers;
}