Custom Roll up With Apex Trigger.

Sometimes we have Requirement to have a number of Counts of Contact on Account, just like Rollup Field Salesforce. But Salesforce has provided Rollup Summary Field on the Master-Detail Object. Below is Sample code for the Same.

Apex Trigger :

trigger trgContactTrigger on Contact (before insert, after insert, before update,after update,after Delete) 
{
ContactTriggerHandler objClass = new ContactTriggerHandler();
objClass.runTrigger();
    
}

Apex Class:

Public class ContactTriggerHandler{

    public void runTrigger() {
        // Method will be called to handle Before Insert events
        if (Trigger.isBefore && Trigger.isInsert) {
            onBeforeInsert((List < Contact> ) trigger.new, null);
        }
        
        // Method will be called to handle Before Update events
        if (Trigger.isBefore && Trigger.isUpdate) {
            onBeforeUpdate((List < Contact> ) trigger.new, (Map < Id, Contact> ) trigger.OldMap);
        }
        
        if (Trigger.isAfter && Trigger.isInsert) {
            onAfterInsert((List < Contact> ) trigger.new, null);
        }
        
        if (Trigger.isAfter && Trigger.isUpdate) {
            onAfterUpdate((List < Contact> ) trigger.new, null);
        }
        
        if (Trigger.isAfter && Trigger.isDelete) {
            onAfterDelete((List < Contact> ) trigger.OldMap.values(), null);
        }
    }
    
    // Method calls all the methods required to be executed before insert
    public void onBeforeInsert(List < Contact> lstTriggerNew, Map < Id, Contact> mapTriggerOld) {
    
    }
    
    // Method calls all the methods required to be executed before insert
    public void onAfterUpdate(List < Contact> lstTriggerNew, Map < Id, Contact> mapTriggerOld) {
    }
    
    // Method calls all the methods required to be executed before insert
    public void onAfterInsert(List < Contact> lstTriggerNew, Map < Id, Contact> mapTriggerOld) {
        updateContactCountThroughTrigger(lstTriggerNew, mapTriggerOld);
    }
    
    // Method calls all the methods required to be executed after delete
    public void onAfterDelete(List < Contact> lstTriggerNew, Map < Id, Contact> mapTriggerOld) {
        updateContactCountThroughTrigger(lstTriggerNew, mapTriggerOld);
    }
    
    // Method calls all the methods required to be executed before update
    public void onBeforeUpdate(List < Contact> lstTriggerNew, Map < Id, Contact> mapTriggerOld) {
    
    }
    
    public void updateContactCountThroughTrigger(List < Contact> lstTriggerNew, Map < Id, Contact> mapTriggerOld){
        Set< Id > setOfAccountID = new Set< Id >();
        if(lstTriggerNew!= null){
            For(Contact objCon : lstTriggerNew){
                if(objCon.AccountId != null)
                  setOfAccountID.add(objCon.AccountId);  
            }
            if(setOfAccountID == null || setOfAccountID.isEmpty())
            return;
            Integer ContactCount ;

            List< Account > lstofAccount = new List< Account >();
            For (Account objAcc :[Select id , (Select id,AccountId FROM Contacts), No_of_Contact_Trigger__c FROM  Account WHERE ID IN : setOfAccountID]){

                ContactCount= 0; 
                For (Contact objContact : objAcc.Contacts){
                    if(objContact.AccountId != null )
                    ContactCount++;
                }
                objAcc.No_of_Contact_Trigger__c =ContactCount;
                lstofAccount.add(objAcc);    
            }
                
            if(!lstofAccount.IsEmpty())
            update lstofAccount;
        }
        
    }

}

This Code is Tested in my personal Dev org. Please let me know if you have any suggestions for this.

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