淨的LINQ集團通過加入

Question

我有下面的代碼：

Departement[] dept = { 
    new Departement {Id = 'S', Name = "Sales" }, 
    new Departement {Id = 'R', Name = "R&D" }, 
    new Departement {Id = 'M', Name = "Marketing" }, 
    new Departement {Id = 'L', Name = "Logistics" }, 
}; 

Employee[] emp = { 
    new Employee {Id = 7, Name = "Peter Smith", Departement = 'S'}, 
    new Employee {Id = 9, Name = "Sam Brown", Departement = 'R'}, 
    new Employee {Id = 12, Name = "John Black", Departement = 'S'}, 
    new Employee {Id = 21, Name = "Sally White", Departement = 'S'}, 
    new Employee {Id = 18, Name = "Diego Maley", Departement = 'R'}, 
    new Employee {Id = 327, Name = "Anna Brown", Departement = 'M'} 
}; 

var res = from d in dept 
      from e in emp 
      join e in emp on d.Id equals e.Departement into cs 
      select new 
      { 
       Id = e.Id, 
       Name = e.Name, 
       count = cs.Count(), 
       departement = e.Departement 
      }; 

foreach (var p in res) 
{ 
    Console.WriteLine("{0} {1} {2}", p.Id, p.Name, p.departement); 
} 

怎麼會有我改變我的代碼，以便輸出如下：

S: Sales -> 3 employees 

    7: Peter Smith 

    12: John Black 

    21: Sally White 

R: R&D -> 2 employees 

    9: Sam Brwon 

    18: Diego Malley 

M: Marketing -> 1 employees 

    32: Anna Brown 

L: Logistics -> 0 employees 

Answer 1

你需要一個group by條款，另有foreach迴路打印員工：

var res = from d in dept 
      join e in emp on d.Id equals e.Departement into cs 
      from e in cs.DefaultIfEmpty() 
      group e by d into g 
      select new 
      { 
       Department = g.Key, 
       Employees = g.Where(x => x != null).ToList() 
      }; 

foreach (var p in res) 
{ 
    Console.WriteLine("{0} {1} {2}", p.Department.Id, p.Department.Name, p.Employees.Count); 
    foreach (var e in p.Employees) 
    { 
     Console.WriteLine("{0} {1}", e.Id, e.Name); 
    } 
}