How to avoid apex `CPU time limit exceeded` by using map based query?

Question

I have the following piece of source code:

List<Account> accountsList = ([SELECT id FROM Account]); 
for(Account account: accountsList) { 
    List<CustomObject1__c> allCustomObjects1 = ([SELECT Id, Account FROM CustomObject1__c where AccountName =:account.Id]); 
    List<CustomObject2__c> allCustomObjects2 = ([SELECT Id, Account FROM CustomObject2__c where AccountName =:account.Id]);
    for(CustomObject2__c cObj2 :allCustomObjects2) { 
        List<CustomObject3__c> allCustomObject3ForCobj1 = new List<CustomObject3__c>(); 
        List<CustomObject3__c> allCustomObject3ForCobj2 = cObj2.CustomsObject3__r; 
        if(allCustomObjects1.size() == allCustomObject3ForCobj2.size()) { 
            continue; 
        } 
        if(allCustomObject3ForCobj2.size() > 0) { 
            delete allCustomObject3ForCobj2; 
        } 
        for(CustomObject1__c cObj1 :allCustomObjects1) { 
            CustomObject3__c cObj3 = new CustomObject3__c(); 
            cObj3.CustomObject1__c = cObj1.Id; 
            cObj3.CustomObject2__c = cObj2.Id; 
            allCustomObject3ForCobj1.add(cObj3);  
        } 
        insert allCustomObject3ForCobj1; 
    } 
}

How can I avoid nested for loops and use Map instead?

Answer 1

Here is the example how to do it this is not complete solution but give you an idea how to do it. Please don't do DML or soql inside for loop create a list and do that action outside of the loop.

Map<ID, Account> accountMap = new Map<ID, Account>([SELECT Id, Name FROM Account LIMIT 50000]);
List<CustomObject1__c> allCustomObjects1 = ([SELECT Id, Account FROM CustomObject1__c where AccountName IN:accountMap.keySet()]); 
List<CustomObject2__c> allCustomObjects2 = ([SELECT Id, Account FROM CustomObject2__c where AccountName  IN:accountMap.keySet()]);

Map<Id,List<CustomObject1__c>> object1map = new Map<Id,List<CustomObject1__c>>();

for(CustomObject1__c obj1 : allCustomObjects1){
    if(object1map.get(obj1.AccountName) == NULL){
        List<CustomObject1__c> tempList = new List<CustomObject1__c>();
        tempList.add(obj1);
        object1map.put(obj1.AccountName,tempList);
    }
    else{
        List<CustomObject1__c> tempList = object1map.get(obj1.AccountName);
        tempList.add(obj1);
        object1map.put(obj1.AccountName,tempList);
    }
}
Map<Id,List<CustomObject2__c>> object2map = new Map<Id,List<CustomObject2__c>>();
for(CustomObject2__c obj2 : allCustomObjects2){
    if(object2map.get(obj2.AccountName) == NULL){
        List<CustomObject2__c> tempList = new List<CustomObject2__c>();
        tempList.add(obj2);
        object1map.put(obj2.AccountName,tempList);
    }
    else{
        List<CustomObject2__c> tempList = object2map.get(obj2.AccountName);
        tempList.add(obj2);
        object1map.put(obj2.AccountName,tempList);
    }
}

for(Id accountId : accountMap.keyset()){
    List<CustomObject1__c> obj1List = object1map.get(accountId);
    List<CustomObject2__c> obj2List = object2map.get(accountId);
    // ==== Your code here for business logic==========
    // prepare list for DMLS

}

// ============ DML here ===========