Hi Ishan,

I modified the code

trigger ConcatenateFields on ChildObject__c(after insert,after update){
List<ParentObject__c> parentObjList = new List<ParentObject__c>();
List<ParentObject__c> parentObjListToBeUpdated = new List<ParentObject__c>();
List<ParentObject__c> parentObjListNULL = new List<ParentObject__c>();

public List<Id> listIds = new List<Id>();
for(ChildObject__c childObj : Trigger.new){
listIds.add(childObj.ParentObjectID__c);
}

parentObjList = [SELECT id,Name,(SELECT ID, Field1__c,Field2__c,Field3__c FROM ChildObjects__r) FROM ParentObject__c WHERE ID IN :listIds];
for(ParentObject__c parentObj : parentObjList){
parentObj.ParentField__c = NULL;
parentObjListNULL.add(parentObj);
}
if(parentObjListNULL.size()>0){
update parentObjListNULL;
}
for(ParentObject__c parentObj : parentObjList){
for(ParentObject__c childObj : parentObj.ChildObjects__r){
if(parentObj.ParentField__c == NULL){
parentObj.ParentField__c = '('+childObj.Field1__c + ' ' + childObj.Field2__c + ' ' + childObj.Field3__c + ')';
}
else{
parentObj.ParentField__c += ' AND ('+childObj.Field1__c + ' ' + childObj.Field2__c + ' ' + childObj.Field3__c + ')';
}
}
parentObjListToBeUpdated.add(parentObj);
}
if(parentObjListToBeUpdated.size()>0){
update parentObjListToBeUpdated;
}
}

As you can see, the child are not hardcoded. it is iterating within for loop for the number of childs that the parent has. It will iterate that no of times and concatenate the field values also that no of times.

NOTE: I'm fetching the childs on the basis of this query

parentObjList = [SELECT id,Name,(SELECT ID, Field1__c,Field2__c,Field3__c FROM ChildObjects__r) FROM ParentObject__c WHERE ID IN :listIds];

And this parentObjList is iterating in the loop, so it will iterate the desired no of times as many childs are present.

If this post is helpful please throw Kudos.If this post solves your problem kindly mark it as solution.

Thanks