Undercover Maps

Posted on January 23, 2014 by Tony Scott

The Map class is probably the most useful collection on the Salesforce platform.

When you combine a Map with a SOQL query you have a really cool tool for automatically populutating a Map of SObjects keyed on Id using a special Map constructor:

Map<Id, Account> accountMap = new Map<Id, Account>([Select Id, Name From Account]);

This is well documented (and really useful for bulk loading foreign objects in triggers) but it turns out you can use this map constructor to populate a Map from any list of SObjects.

In the following example we have a query that loads Accounts as well as Opportunities. You can use the Map constructor to load the subquery results into a Map as follows:

// Query Accounts and Opportunities into a Map
Map<Id, Account> accountMap = new Map<Id, Account>([Select Id, Name, (Select Id, Name From Opportunities) From Account]);

// Iterate over the Map keys
for (Id key : accountMap.keySet())
{
    Account acc = accountMap.get(key);

    System.debug('Account: ' + key + ' => ' + acc.Name);

    // Load the Opportunities into a Map
    Map<Id, Opportunity> oppMap = new Map<Id, Opportunity>(acc.Opportunities);

    // Iterate over the Map Keys
    for (Id key2 : oppMap.keySet())
    {
        Opportunity opp = oppMap.get(key2);

        System.debug('Opportunity: ' + key2 + ' => ' + opp.Name);
    }
}

You can do the same with Dynamic SOQL with one subtle difference, you need to check for Nulls:

// Query to execute
String query = 'Select Id, Name, (Select Id, Name From Opportunities) From Account';

// Query Accounts and Opportunities into a Map
Map<Id, SObject> sObjectMap = new Map<Id, SObject>(Database.query(query));

// Iterate over the Map keys
for (Id key : sObjectMap.keySet())
{
    SObject so = sObjectMap.get(key);

    System.debug('Account SObject: ' + key + ' => ' + so.get('Name'));

    // Load the Opportunities into a Map
    List<SObject> sos = so.getSObjects('Opportunities');

    // Check the Map for Null in case the Account has no Opportunities
    if (sos != null)
    {
        Map<Id, SObject> soMap2 = new Map<Id, SObject>();

		// Iterate over the Map keys
        for (Id key2 : soMap2.keySet())
        {
            SObject so2 = soMap2.get(key2);

            System.debug('Opportunity SObject: ' + key2 + ' => ' + so2.get('Name'));
        }
    }
}

The Map constructor also allows you to use a Dynamic SOQL query to load into Map of concrete SOBjects by casting it to a List:

String query = 'Select Id, Name From Account';

Map<Id, Account> accountMap = new Map<Id, Account>((List<Account>)Database.query(query));

A Final Word of Warning:

Always exercise caution when using undocumented features within Salesforce. They may break without warning.

Undercover Maps

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