Comparing Values between two lists

Question

I'm having a custom object say obj.In my apex class I'm having two lists of this object

In list<obj__c> list1 ---- I'll be getting say suppose 3 Records &
In list<obj__c> list2 ---- I'll be getting say suppose 2 Records(this 2 records are of list1 records and will not be greater than list1).

My requirement here is I want to insert the 3rd record which is not present in list2. Every Record consists of unique Name.What would be the best way to solve this.Any help on this pls

My approach is something like this

if(list1.size() > list2.size()){
    //map my name
}

Answer 1

If I understand you correctly, you want to check if values exists in lists,

Since you have a unique name, it's best to leverage that uniqueness in combination with a map, you start of by adding all the values in your lists to 2 maps.

Map<String, Obj__c> objMap1 = new Map<String, Obj__c>();
Map<String, Obj__c> objMap2 = new Map<String, Obj__c>();

// List 1
for(Obj__c o : list1)
{
    objMap1.put(o.UniqueName__c, o);
}

// List 2
for(Obj__c o : list2)
{
    objMap2.put(o.UniqueName__c, o);
}

// Now you can easily check if that value is in your map by doing.
objMap1.containsKey('WhateverYouWantToCompare');
// or
objMap2.containsKey(newObj.UniqueName__c);

// ... do your logic

Here is the documentation for Maps and Sets try to use this as much as possible to reduce the number of script statements you have for manually looping over lists just to check if values exists or not.

Answer 2

The maps seems a little unnecessary here; I would leverage Sets instead.

Set<Obj__c> set1 = new Set<Obj__c>(list1);
Set<Obj__c> set2 = new Set<Obj__c>(list2);

for(Obj__c o : set1){
     if(!set2.contains(o) ){
          //your logic
     }
}