Parent-Child Update Trigger - Update Field on Parent Object when Field Changes on Child (Booleans)

Question

• There are 2 custom objects involved.
• Project__c is the parent, Project_Contact__c is the child.
• Both objects contain a field called Survey_Sent__c.
• Whenever 'Survey Sent' is updated on the child, I'd like my trigger to fire and update 'Survey Sent' on the parent.

============ Code so Far =========

trigger UpdateProjectSurveySent on Project_Contact__c (before update) {
    if(trigger.isUpdate){ // if trigger fired due to an update

        List<Id> parentIds = new List<id>(); // create a list variable to that holds Ids
        List<Id> childIds = new List<Id>(); // list to hold child Ids

        for(Project_Contact__c Pc : trigger.new){ // cycle through child records, grab Ids, store child Ids in trigger.new
            parentIds.add(Pc.Project__c.Id); // then add parent Ids to our parent Id list. Lists are ordered. This is kind of a map stucture. 
            childIds.add(Project_Contact__c.Id);
        }

        List<Project__c> pj = [SELECT Id, Survey_Sent__c FROM Project__c WHERE Id in: parentIds]; // fill list3 with projects that have an Id stored in pjIdList

        for(Project__c p : pj){ // cycle list3 projects, and make Survey Sent fields match.
            p.survey_sent__c = pj.survey_sent__c;
        }
    }
}

Answer 1

You should try learn how to use Map, it's very useful I used it all the time. So first you need to check if the value of the project contact survey change (don't need to update the project if the survey didn't change). Add the project to a map, then retrieve the project via SOQL, then loop to project contact again and see if we need to update related project found. It should look something like :

trigger UpdateProjectSurveySent on Project_Contact__c (before update) {
    if(trigger.isUpdate){ // if trigger fired due to an update

        Map<Id, Project__c> projects = new Map<Id, Project__c>();

        for(Project_Contact__c Pc : trigger.new){
            if (pc.Survey_Sent__c != Trigger.oldMap.get(pc.Id).Survey_Sent__c){  //do we need to update Project ? 
              projects.put(Pc.Project__c, null);
            }
        }
        //get projects
        if (projects.isEmpty()){
          projects = new Map<Id, Project__c>([SELECT Id, Survey_Sent__c FROM Project__c WHERE Id in: projects.keySet()]); 
        }

         for(Project_Contact__c Pc : trigger.new){ \
            Project__c p = projects.get(pc.Project__c);
            if (p != null){
              p.survey_sent__c = Pc.survey_sent__c;
            }
        }

        update projects.values();
    }
}