linq to sql recursive query

Question

EmployeeId  Name  ManagerId
------------------------------
1           A     null
2           B     null
3           C     1
4           D     3
5           E     2
         


        

Answer 1

I'm not sure if this is exactly what you want, but here is one recursive method that uses some linq that makes sure not to enter an infinite loop:

    public static IEnumerable GetTreeForEmployeeNumber(this IEnumerable source, int startingId) {
        var result = source.Where(x => x.EmployeeId == startingId).FirstOrDefault();
        if (result != null) {
            var resultAsE = new [] { result };
            if (!result.ManagerId.HasValue)
                return resultAsE;
            return resultAsE.Union(source.Except(resultAsE).GetTreeForEmployeeNumber(result.ManagerId.Value));
        }
        return new Employee [] { };
    }

If you have linqpad installed you can test this with the following script:

void Main()
{
    var lst = new [] {
        new Extensions.Employee{ EmployeeId = 1, Name = "A", ManagerId = null }, 
        new Extensions.Employee{ EmployeeId = 2, Name = "B", ManagerId = null }, 
        new Extensions.Employee{ EmployeeId = 3, Name = "C", ManagerId = 1 }, 
        new Extensions.Employee{ EmployeeId = 4, Name = "D", ManagerId = 3 }, 
        new Extensions.Employee{ EmployeeId = 5, Name = "E", ManagerId = 2 }
    };

    lst.GetTreeForEmployeeNumber(4).Dump();
}

public static class Extensions {

    public class Employee {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public int? ManagerId { get; set; }
    }

    public static IEnumerable GetTreeForEmployeeNumber(this IEnumerable source, int startingId) {
        var result = source.Where(x => x.EmployeeId == startingId).FirstOrDefault();
        if (result != null) {
            var resultAsE = new [] { result };
            if (!result.ManagerId.HasValue)
                return resultAsE;
            return resultAsE.Union(source.Except(resultAsE).GetTreeForEmployeeNumber(result.ManagerId.Value));
        }
        return new Employee [] { };
    }
}