Applying Lead assignment rule when inserting bulk data from data loader (Trigger solution)

Problem : When inserting lead from data loader lead reassignment rules are                        not working on records.

solution : when you are using lead assignment rules you have to check the                        checkbox Assign using active assignment rule on lead and it                                 works fine . 

Problems arise when you have to insert bulk data. In this case the lead assignment rule does not work . 

So what i do i found this solution by writing after insert trigger on lead . I use apex DML operation. Here useDefaultRule  is the default assignment rule set by the user. 

        

Here is my code :

,

                   Trigger onAfterInsert on Lead(After insert)

                    public static List<Lead> leads = new List<Lead>();

                        {

                            for (Lead l : Lead_ids)

                                {

                                    leads.add(new Lead(Id = l.Id));

                                }

                             Database.DMLOptions dmo = new Database.DMLOptions();

                             dmo.assignmentRuleHeader.useDefaultRule = true;

                             Database.update(leads, dmo);

                        }

  Thanks,
  Lovesalesforceyes.