how to update parent field from child

Question

I got 2 objects Service_Request__c(Parent) and Service_Line__c(Child). I'm trying to do is update a field of parent object from child.based on the following condition. In the following code, I'm not getting how to update the parent. please suggest how to proceed.

public class StatusClosedHandler {
public static void statuschange (String RecordId){
    integer count = 0;
    List<Service_Line__c> sLine = new List<Service_Line__c>();
 for(Service_Line__c sl : [Select id, Name, Status__c,Line_Type__c, Service_Request__r.Status__c,Service_Request__r.Name from Service_Line__c WHERE Service_Request__c = :RecordId ]){
     if(sl.Status__c == 'Completed'){
         count++; 
}
         if(count == 3){  
         sl.Service_Request__r.Status__c = 'Closed';   
}
         sLine.add(sl);
}
         update sLine;
}

}

Answer 1

You need to define a parent object in for loop and then added to parent list and upate this

public class StatusClosedHandler { 
     public static void statuschange    (String RecordId){ 
        integer count = 0;               List<Service_Request__c> srequest = new List<Service_Request__c>();

         for(Service_Line__c sl : [Select id, Name, Status__c,Line_Type__c, Service_Request__r.Status__c,Service_Request__r.Name from Service_Line__c WHERE Service_Request__c = :RecordId ]){
             if(sl.Status__c == 'Completed'){ 
                   count++;
              } 
              if(count == 3){
                    Service_Request__c sr = new         Service_Request__c();
                     sr.id = sl.Service_Request__c;
                      sr.status__c = 'Closed';
                       srequest.add(sr);
                } 
    }
               If(!srequest.isEmpty())
                      update srequest; 
   }
}

Answer 2

Basically, you need to create a new variable for the Parent and update it.

public class StatusClosedHandler {
public static void statuschange (String RecordId){
    List< Service_Request__c> servRequestList = new List< Service_Request__c>(); //list of Parent
    integer count = 0;
    List<Service_Line__c> sLine = new List<Service_Line__c>();
 for(Service_Line__c sl : [Select id, Name, Status__c,Line_Type__c, Service_Request__r.Status__c,Service_Request__r.Name from Service_Line__c WHERE Service_Request__c = :RecordId ]){
     if(sl.Status__c == 'Completed'){
         count++; 
     }
         if(count == 3){
           Service_Request__c thisService = new Service_Request__c();
           thisService.ID = sl.Service_Request__c;
           thisService.Status__c = 'Closed';  
           servRequestList.add(thisService)
         }
         sLine.add(sl);
 }
 if (!servRequestList.isEmpty()) {
     update servRequestList;
 }
}