public static void Main(string[] args)
{
var querySyntax = from student in Student.GetAllStudents()
join address in Address.GetAllAddresses()
on student.AddressId equals address.Id
join department in Department.GetAllDepartments()
on student.DepartmentId equals department.Id
select new
{
StudentName = student.Name,
Department = department.Name,
Road = address.Street
};
foreach (var student in querySyntax)
{
Console.WriteLine(student.StudentName + " " + student.Department + " " + student.Road);
}
}
public static void Main(string[] args)
{
// Linq's Join is equivalent to SQL's Inner Join
// Linq's GroupJoin is equivalent to SQL's Outer Join
// Left Outer Join and Right Outer Join can be performed by exchanging data source
// Cross Join doesn't require common property. It generates cartesian products of the collection
var joinQuerySyntax = from dept in Department.GetAllDepartments()
join std in Student.GetAllStudents()
on dept.ID equals std.DepartmentId
select new { Name = std.Name, Department = dept.Name };
//foreach(var std in joinQuerySyntax)
//{
// Console.WriteLine(std.Name + " " + std.Department);
//}
var groupJoinQuerySyntax = from dept in Department.GetAllDepartments()
join std in Student.GetAllStudents()
on dept.ID equals std.DepartmentId
into StudentGroups // List of children. Here it is list of Student
select new { Department = dept.Name, StudentGroups = StudentGroups };
// from p in Parent
// join c in Child
// on p.Id equals c.Id into GROUPJOIN
// select new { NewParent = Parent, NewChildren = GROUPJOIN};
// NewChildren is a list of Children. It can be empty if there is no children
//Outer Foreach is for all department
//foreach (var item in groupJoinQuerySyntax)
//{
// Console.WriteLine("Department :" + item.Department);
// //Inner Foreach loop for each student of a department
// foreach (var student in item.StudentGroups)
// {
// Console.WriteLine(" StudentID : " + student.Id + " , Name : " + student.Name);
// }
//}
var flattenedQuerySyntax = from dept in Department.GetAllDepartments()
join std in Student.GetAllStudents()
on dept.ID equals std.DepartmentId
into StudentGroups
from student in StudentGroups.DefaultIfEmpty()
select new { Department = dept, StudentName = student?.Name };
//foreach(var item in flattenedQuerySyntax)
//{
//Console.WriteLine("Department - " + item.Department.Name + " . Student - " + item.StudentName);
//}
var crossJoin = from std in Student.GetAllStudents()
from dept in Department.GetAllDepartments()
select new
{
Name = std.Name,
Depatment = dept.Name
};
Console.WriteLine(crossJoin.LongCount()); // Number of Student * Number of Department
}
