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How to achive rollupsummary by using of agregate functions?(lookup relation between custom object)

How to achive rollupsummary by using of agregate functions?(lookup relation between custom object)
obj1 - count__c(custom field) - will calculate the total amount__c
obj2 - having lookup to obj1 - amount__c (available in obj2)

How can I achive this by aggregate functions?
Best Answer chosen by sen19
Tikam.SangwaniTikam.Sangwani
Hi Ananga,

You need to write trigger on obj2. Please find below code where I used obj1 as parent and obj2 as child:

trigger trigRollup on obj2__c (after insert, after update, after delete) {
    
            set<id> parentIds = new set<id>();
            if(Trigger.isDelete)
            {
                for(obj2__c objchild : Trigger.Old)
                {
                    parentIds.add(objchild.LookupField__c);
                }
            }
            else
            {
                for(obj2__c objchild : Trigger.New)
                {
                    parentIds.add(objchild.LookupField__c);
                }
            }
        
            list<obj1__c> lstObj1 = new list<obj1__c>();
    
            list<AggregateResult> lstAgrRes = [select LookupField__r.Id parentId,sum(amount__c) total from obj2__c where LookupField__r.id in :parentIds Group By LookupField__r.Id];
    
            for(AggregateResult agr : lstAgrRes){

                obj1__c objmaster = new obj1__c();
                
                objmaster.Id = (Id)agr.get('parentId');
                
                objmaster.Total_Amount__c = (Decimal) agr.get('total');
                
                lstObj1.add(objmaster);
            }
            if(lstObj1.size() > 0)
                update lstObj1;
}

Please let me know for any query on this and mark this as best answer if it helps you . 

Best Regards 
Tikam Sangwani

All Answers

Tikam.SangwaniTikam.Sangwani
Hi Ananga,

You need to write trigger on obj2. Please find below code where I used obj1 as parent and obj2 as child:

trigger trigRollup on obj2__c (after insert, after update, after delete) {
    
            set<id> parentIds = new set<id>();
            if(Trigger.isDelete)
            {
                for(obj2__c objchild : Trigger.Old)
                {
                    parentIds.add(objchild.LookupField__c);
                }
            }
            else
            {
                for(obj2__c objchild : Trigger.New)
                {
                    parentIds.add(objchild.LookupField__c);
                }
            }
        
            list<obj1__c> lstObj1 = new list<obj1__c>();
    
            list<AggregateResult> lstAgrRes = [select LookupField__r.Id parentId,sum(amount__c) total from obj2__c where LookupField__r.id in :parentIds Group By LookupField__r.Id];
    
            for(AggregateResult agr : lstAgrRes){

                obj1__c objmaster = new obj1__c();
                
                objmaster.Id = (Id)agr.get('parentId');
                
                objmaster.Total_Amount__c = (Decimal) agr.get('total');
                
                lstObj1.add(objmaster);
            }
            if(lstObj1.size() > 0)
                update lstObj1;
}

Please let me know for any query on this and mark this as best answer if it helps you . 

Best Regards 
Tikam Sangwani
This was selected as the best answer
sen19sen19
thanks