Working with Lead Conversion with trigger

Question

I am trying to write a trigger on lead which gives result as Whenever i update a lead, that should be converted into account, contact and Opportunity. I wrote a trigger, but it is showing following error which shown in pic. and also please follow my code.

Trigger:

trigger LeadConvert_Trigger on Lead (after update) {

    for(Lead leed : Trigger.New){
        Database.LeadConvert lcon= new Database.LeadConvert();
        lcon.setLeadId(leed.Id);

        LeadStatus convertStatus=[Select id, MasterLabel from LeadStatus where isConverted=true];
        lcon.setconvertedStatus(convertStatus.MasterLabel);
        Database.LeadConvertResult result= Database.convertLead(lcon);
    }
}

Error

Answer 1

use this code:

trigger:

trigger LeadConvert_Trigger on Lead (after update) {

if(p.firstRun)
    {

  p.firstRun = false;

    for(Lead leed : Trigger.New){
        Database.LeadConvert lcon= new Database.LeadConvert();
        lcon.setLeadId(leed.Id);

        LeadStatus convertStatus=[Select id, MasterLabel from LeadStatus where isConverted=true];
        lcon.setconvertedStatus(convertStatus.MasterLabel);
        Database.LeadConvertResult result= Database.convertLead(lcon);
    }

    }

class:

public class p { 
   public static boolean firstRun = true; 
}

Answer 2

Ok. For some reason, after you convert the lead, salesforce edits it again (probably to set isConverted to true).

What you need to do is a slightly change on you trigger:

Trigger LeadConvert_Trigger on Lead (after update) {
     LeadStatus convertStatus = [
          select MasterLabel
          from LeadStatus
          where IsConverted = true
          limit 1
     ];
     List<Database.LeadConvert> leadConverts = new List<Database.LeadConvert>();

     for (Lead leed: Trigger.new) {
          if (!leed.isConverted) {
               Database.LeadConvert lc = new Database.LeadConvert();

               lc.setLeadId(leed.Id);
               lc.setConvertedStatus(convertStatus.MasterLabel);

               leadConverts.add(lc);
          }
     }

     if (!leadConverts.isEmpty()) {
          List<Database.LeadConvertResult> lcr = Database.convertLead(leadConverts);
     }
}

Thanks, @Mahmood for providing the link. Also, please check deadlypenguin's blog for a more thoroughly explanation.