Apex Map within a Map

Question

I need to have a Map within a Map in one of my Triggers. I know how to build the map initially as that is documented:

Map<Id, Map<Id, Addendum__c>> addendums = new Map<Id, Map<Id, Addendum__c>>{};

However, I'm having trouble actually assigning values to the multi-dimensional map. Normally I would use .put() to place values into a single-dimension map. Maybe I'm still supposed to use that function, but I can't for the life of me figure out the correct syntax.

I have tried the following which do not work:

addendums.put(addendum.Opportunity__c, addendum.Id, addendum);

addendums.put(addendum.Opportunity__c, (addendum.Id, addendum));

Does anyone know how to do this?

Thanks!

Answer 1

Using your sample code will work, though of course the second level map can only ever have one entry, if you're in a situation where you may need more then the code below will do the trick for you:

    // This line creates the map in the proper format
    Map<Id,Map<Id,Addendum__c>> addendums = new Map<Id,Map<Id,Addendum__c>>{};
    
    // This for loop goes through each addendum and first places it into a single dimension map.  
    // Once that map is created, it is placed into the final multi-dimensional
    for(Addendum__c addendum : [SELECT Id,Opportunity__c FROM Addendum__c WHERE Opportunity__c IN :oppBatch])
    {
        if(addendums.get(addendum.Opportunity__c) == null)
        {
            addendums.put(addendum.Opportunity__c, new Map<Id, Addendum__c>{addendum.Id => addendum);
        }
        else
        {
            addendums.get(addendum.Opportunity__c).put(addendum.Id, addendum);
        }
    }

As you can see this uses get() on the first map to get the correct second-level map in which we want to add an addendum.

Answer 2

The method that Josh provided works fine. If you'd like to remove one line of code, you can using the following approach:

Map<Id, Map<Id,Addendum__c>> addendums = new Map<Id,Map<Id,Addendum__c>>();
for(Addendum__c addendum : [SELECT Id,Opportunity__c FROM Addendum__c WHERE Opportunity__c IN :oppBatch]){
    addendums.put(addendum.opportunity__c, new Map<Id, Addendum__c>{addendum.id => addendum});
}

I'm not aware of a more efficient approach than this one.

Answer 3

I found a way to do this, although I'm not sure whether it's the most efficient method or not. So if you have a better solution, please let me know, I'll transfer the "solution" credit to you.

What I did was assign the first map, and then place that map within the final map.

// This line creates the map in the proper format
Map<Id,Map<Id,Addendum__c>> addendums = new Map<Id,Map<Id,Addendum__c>>{};

// This for loop goes through each addendum and first places it into a single dimension map.  
// Once that map is created, it is placed into the final multi-dimensional
for(Addendum__c addendum : [SELECT Id,Opportunity__c FROM Addendum__c WHERE Opportunity__c IN :oppBatch]){
    Map<Id,Addendum__c> thisAddendum = new Map<Id,Addendum__c>{ addendum.Id => addendum };
    addendums.put(addendum.Opportunity__c,thisAddendum);
}