使用联接和聚合函数的linq查询

Question

I want to write a linq query which retrieves the data in the following format.

Assume that there are two tables - Department and Employee

Department
Dept_id| Manager_id   

Employee
Emp_id| Dept_id| Emp_data

The relationship between Department and Employee table is one to many. The Department table also stores the manager employee id in that particular department. So Manager_id is nothing but the employee_id .

Now I want to get the data as follows

Dept_id, Manager_id, Emp_data(data of Manager_id), Count(employees in that department)

If I do the join on two tables i can get data of Manager but unable to get the count of all employees in that department. Any help would be appreciated.

Answer 1

You could do something like this:

var result= 
    (
        from dep in db.Department
        join emp in db.Employee
            on dep.Manager_id equals emp.Emp_id
        select new
        {
            dep.Dept_id,
            emp,
            NumberOfEmp= db.Employee.Count(c=>c.Dept_id==dep.Dept_id)
        }
    ).ToList();

Where db is the linq data context

Answer 2

You could do a group join. If you have a preferred handcoded SQL statement that you would like to be generated from your LINQ query. You may want to experiment a bit with different formats to see which one allows you to generate the "best" SQL.

var result = from d in context.Departments
             join e in context.Employees on d.dept_id equals e.dept_id into g
             select new {
                 dept_id = d.dept_id,
                 manager_id = d.manager_id,
                 manager_data = g.Single(x => x.emp_id == d.manager_id).emp_data,
                 employee_count = g.Count()
             };

or

var result = from d in context.Departments
             join e in context.Employees on d.dept_id equals e.dept_id into g
             from m in g where m.emp_id == d.manager_id
             select new {
                 dept_id = d.dept_id,
                 manager_id = d.manager_id,
                 manager_data = m.emp_data,
                 employee_count = g.Count()
             };