A Beginner's Guide to Salesforce Apex Maps

TL;DR

Apex Maps are powerful key-value pair collections that enable efficient data lookups and organization. They store unique keys that map to values of any data type, making them essential for Salesforce development.

What Are Apex Maps?

Think of a Map as a phone book or dictionary. Just like you look up a person's name (the key) to find their phone number (the value), Maps in Apex store key-value pairs where each unique key maps to exactly one value.

Why Use Maps?

Maps are incredibly useful when you need to:

• Quickly look up data without iterating through a list
• Associate related information (like Account IDs with Account records)
• Eliminate duplicate entries (keys are always unique)
• Organize data in a logical, accessible way

Declaring Apex Maps

The basic syntax for declaring a Map:

Map<String, Integer> personAges = new Map<String, Integer>();

Essential Map Operations

Adding Items with put()

Map<String, Integer> scores = new Map<String, Integer>();
scores.put('Alice', 95);
scores.put('Bob', 87);

Retrieving Values with get()

Integer aliceScore = scores.get('Alice'); // Returns 95
Integer notFound = scores.get('Charlie'); // Returns null

Checking for Keys with containsKey()

if (scores.containsKey('Alice')) {
    System.debug('Alice has a score!');
}

Real-World Example

Map<Id, Account> accountMap = new Map<Id, Account>(
    [SELECT Id, Name FROM Account LIMIT 100]
);
 
for (Contact con : [SELECT AccountId FROM Contact]) {
    if (accountMap.containsKey(con.AccountId)) {
        Account acc = accountMap.get(con.AccountId);
        System.debug('Contact belongs to: ' + acc.Name);
    }
}

Best Practices

1. Always check for null when using get()
2. Use containsKey() before accessing values
3. Bulkify your code by using Maps in triggers
4. Choose the right key type (usually Id or String)

Common Mistakes to Avoid

• Forgetting that get() returns null for missing keys
• Not using Maps in triggers (processing one record at a time)
• Using the wrong data type for keys
• Assuming order is maintained (Maps are unordered)

Conclusion

Apex Maps are fundamental to writing efficient Salesforce code. Master these basics, and you'll be ready to tackle more complex scenarios in your development journey!