Getting this error while insert 'System.ListException: Before Insert or Upsert list must not have two identically equal elements'

Question

I'm getting the following error 'System.ListException: Before Insert or Upsert list must not have two identically equal elements' when i'm trying below code

Map<Id,SBQQ__QuoteLine__c> parentQuoteLines = new Map<Id,SBQQ__QuoteLine__c>();

for(SBQQ__QuoteLine__c  qli : qliToInsert){

if( String.isBlank(qli.SBQQ__RequiredBy__r.Id) 
                            && !parentQuoteLines .containsKey(qli.Id) 
   &&qliprodCodetoRecordMap.containsKey(qli.SBQQ__Product__c)){
                                parentQuoteLines.put(qli.Id,qliprodCodetoRecordMap.get(qli.SBQQ__Product__c));
                        }

if(!parentQuoteLines .values().isEmpty()){

    insert parentQuoteLines .values(); // Getting error when inserting
}

Answer 1

This:

parentProducts.put(qli.Id, qliprodCodetoRecordMap.get(qli.Id));

or this (more likely what you want):

parentProducts.put(qli.SBQQ__Product__c, qliprodCodetoRecordMap.get(qli.SBQQ__Product__c));

or this (cleaner code version):

SBQQ__QuoteLine__c pqli = qliprodCodetoRecordMap.get(qli.SBQQ__Product__c);
parentProducts.put(pqli.Id, pqli);

would avoid duplicate records but this mixture that you are using will not:

parentProducts.put(qli.Id, qliprodCodetoRecordMap.get(qli.SBQQ__Product__c));