Salesforce APEX is a powerful, strongly-typed programming language that allows developers to customize business logic within the Salesforce platform. However, writing efficient and maintainable APEX code requires adhering to best practices. Below are some key guidelines to follow when developing APEX applications.

1. Follow Governor Limits

Salesforce enforces strict governor limits to ensure efficient resource usage. To avoid hitting these limits:

• Minimize the number of SOQL queries inside loops.
• Use bulkified operations to process multiple records at once.
• Optimize DML statements to reduce the number of database transactions.

2. Use Bulkification Techniques

APEX should be written to handle large data volumes efficiently:

• Use collections (Lists, Sets, Maps) instead of querying or updating records one by one.
• Use FOR loops with bulk SOQL queries to retrieve records efficiently.

Example of Bulkified Code:

List<Account> accountsToUpdate = [SELECT Id, Name FROM Account WHERE Industry = 'Technology'];
for (Account acc : accountsToUpdate) {
    acc.Name = acc.Name + ' - Updated';
}
update accountsToUpdate;  // Bulk DML operation

3. Use Future Methods and Queueable Apex

For long-running or asynchronous operations, use:

• @future methods to perform tasks asynchronously.
• Queueable Apex for complex processing requiring chaining.

Example of Queueable Apex:

public class ProcessLargeData implements Queueable {
    public void execute(QueueableContext context) {
        List<Account> accs = [SELECT Id FROM Account];
        for (Account acc : accs) {
            acc.Name = 'Processed';
        }
        update accs;
    }
}

4. Implement Proper Exception Handling

Use try-catch blocks to manage errors gracefully and avoid unhandled exceptions:

try {
    Account acc = [SELECT Id FROM Account WHERE Name = 'Nonexistent'];
} catch (Exception e) {
    System.debug('Error: ' + e.getMessage());
}

5. Use Apex Triggers Wisely

• Use one trigger per object and delegate logic to a Trigger Handler Class.
• Avoid business logic inside triggers, move it to a helper class.

6. Optimize SOQL Queries

• Use selective queries to improve performance.
• Avoid using SELECT * and retrieve only necessary fields.
• Use indexed fields in WHERE conditions to speed up queries.

7. Write Unit Tests with High Coverage

Salesforce requires at least 75% code coverage for deployment. Best practices for unit tests:

• Use Test.startTest() and Test.stopTest().
• Use @isTest annotation for test classes and methods.
• Test both positive and negative scenarios.

Example of a Simple Test Class:

@isTest
private class AccountTest {
    @isTest
    static void testAccountInsert() {
        Test.startTest();
        Account acc = new Account(Name = 'Test Account');
        insert acc;
        Test.stopTest();
        System.assert(acc.Id != null);
    }
}

Conclusion

Following these best practices ensures that your APEX code is efficient, scalable, and maintainable. By writing optimized, bulkified, and well-tested code, you can build high-performing, and manageable applications on the Salesforce platform.