Question

When writing LINQ queries in C#, I know I can perform a join using the join keyword. But what does the following do?

from c in Companies
from e in c.Employees
select e;

A LINQ book I have say it’s a type of join, but not a proper join (which uses the join keyword). So exactly what type of join is it then?

Answer 1

Multiple “from” statements are considered compound linq statments. They are like nested foreach statements. The msdn page does list a great example here

var scoreQuery = from student in students
                 from score in student.Scores
                 where score > 90
                 select new { Last = student.LastName, score };

this statement could be rewritten as:

SomeDupCollection<string, decimal> nameScore = new SomeDupCollection<string, float>();
foreach(Student curStudent in students)
{
   foreach(Score curScore in curStudent.scores)
   {
      if (curScore > 90)
      {
         nameScore.Add(curStudent.LastName, curScore);
      }
   }
}