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Recursion in Apex

We can use recursion in apex to find a self-lookup hierarchy in a custom object.


Parent__c (This is a lookup to itself i.e Custom_Object__c)

Now, we will try to go inside the n-level deep hierarchy with the help of recursion in the apex.
public static List<Custom_Object__c> retrieveHierarchyRecords(String param1, String param2){
try {
if(String.isBlank(param1)) return null;
if(String.isBlank(param2)) return null;
List<Custom_Object__c> parents = [SELECT Id, Field1__c, Field2__c, Field3__c, Field4__c, Parent__c FROM Custom_Object__c WHERE Field1__c =: param1 AND Field2__c =: param2];
if(parents == null) return null;
if(parents.size() == 0) return null;
List<String> ids = new List<String>();
List<Custom_Object__c> res = new List<Custom_Object__c>();
for(Custom_Object__c p : parents){
List<Custom_Object__c> result = findChildren(ids,res);
return result;
} catch (Exception e) {
throw new AuraHandledException(e.getMessage());
public static List<Custom_Object__c> findChildren(List<String> ids,List<Custom_Object__c> res){
if(ids == null) return res;
List<String> idList = new List<String>();
List<Custom_Object__c> result = [SELECT Id, Field1__c, Field2__c, Field3__c, Field4__c, Parent__c FROM Custom_Object__c WHERE Parent__c IN : ids];
for(Custom_Object__c a: result){
if(idList == null) return res;
if(idList.size() == 0) return res;
return findChildren(idList,res);

In the above example, we are searching for the hierarchy of Custom_Object__c where if Field1__c is empty, then only it would have further children and we have Parent__c which defines the parent lookup id.

This example shows only the retrieval of records, but following this method, we can do much more, such as DML operations also.

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