Question

I am trying to get data from db table called

Departments

Id
Name
ParentId

I want to create hierachical view in a dropdownlist to choose between departments
I want to retrieve the data with linq and bind it to the dropdownlist
any help ?

Answer 1

http://www.scip.be/index.php?Page=ArticlesNET18

worked for me

nice article

GetEmployeesHierarchy() method

I first started creating a new EmployeeHierarchy class. This class contains an Employee entity (the boss) and a collection of child employees.

public class EmployeeHierarchy
{
  public Employee Employee { get; set; }
  public IEnumerable<EmployeeHierarchy> Employees { get; set; }
}

In .NET 3.5 we have LINQ at our’s disposal. So I created a recursive GetEmployeesHierachy function which will start with the director (who does not have to report to anyone, ReportsTo = null) and query all employees which are working for him (ReportsTo == EmployeeId of boss). This will be repeated recursively. Finally this function will return a collection of EmployeeHierarchy objects.

public IEnumerable<EmployeeHierarchy> GetEmployeesHierachy(IEnumerable<Employee> allEmployees, Employee parentEmployee)
{
  int? parentEmployeeId = null;

  if (parentEmployee != null)
    parentEmployeeId = parentEmployee.EmployeeID;

  var childEmployees = allEmployees.Where(e => e.ReportsTo == parentEmployeeId);

  Collection<EmployeeHierarchy> hierarchy = new Collection<EmployeeHierarchy>();

  foreach (var emp in childEmployees)
    hierarchy.Add(new EmployeeHierarchy() { Employee = emp, Employees = GetEmployeesHierachy(allEmployees, emp) });

  return hierarchy;
}

This function can be called after a LINQ to SQL or LINQ to Entities (Entity Framework) query. Make sure to call the ToList() extension method. It is much more performant to first load all data from the database and then convert it to a hierachical structure. By calling the ToList() method all references to the database will be removed.

NorthWindDataContext dc = new NorthWindDataContext();

var employeesHierarchy = GetEmployeesHierachy(dc.Employees.AsEnumerable(), null);

treeViewEmployees.ItemsSource = employeesHierarchy;