System.ListException：在Insert或Upsert列表之前，不能有两个完全相同的元素

Question

我在插入触发器执行的新记录时收到此错误：

  

“System.ListException：在Insert或Upsert列表之前，必须没有两个完全相同的元素”

以下是触发器：

trigger createCETAccount on Account (before update) {
    //trigger runs after the update of an Account record
    //create a set of all the unique Account IDs
    Set<id> AIds = new Set<id>();
    //for each instance of the trigger being fired if the Contact field is not blank 
    //and the Contact Exact Target Send field is not blank and has changed from what it was   previously - add that record's ID to the MTIds Set
    for (Integer i = 0; i < Trigger.new.size(); i++)
    {
        if(Trigger.new[i].Contact_Exact_Target_Send__c != Trigger.old[i].Contact_Exact_Target_Send__c && Trigger.new[i].Contact_Exact_Target_Send__c != null)
        {
            AIds.add(Trigger.new[i].Id);  
        }
    } 

    //query for all the Account records for the unique AIds in the records
    List <Account> aList = new List<Account> ([Select Id, Contact_Exact_Target_Send__c from Account where Id in :AIds]);
    //List all the Contacts associated with the Account
    List <Contact> ContactList = new List <Contact> ([Select Id, AccountId, isPrimary__c from Contact where AccountId in :AIds ORDER BY isPrimary__c ASC, createdDate DESC]);
    //Create a list of ContactExactTarget records
    List <ContactExactTarget__c> CETList = new List<ContactExactTarget__c> ([Select ID, Account__c from ContactExactTarget__c where Account__c in :AIds]);
    List <ContactExactTarget__c> CETList2 = new List<ContactExactTarget__c>;
    //iterate over the list of Account records being processed in the trigger
    for(Account acc: aList){
        //create a new ContactExactTarget send record for each instance
        ContactExactTarget__c objCET = new ContactExactTarget__c();
        objCET.ET_Code__c = acc.Contact_Exact_Target_Send__c;
        objCET.Account__c = acc.Id;
        //add the record to the CETList defined above
        CETList.add(objCET);
    }
    //add the related Contact to the CET record
    for(Contact con : ContactList) {  
        for (ContactExactTarget__c cet : CETList){
            if (con.AccountId  == cet.Account__c)
                cet.Contact__c = con.Id;
            CETList2.add(cet);
        }
    }

    //upsert the list to insert the new records
    upsert CETList2;
}