2484 LLM Anti Patterns 09c7deb4

LLM-Specific Anti-Patterns in Apex

This guide documents systematic errors that LLMs (including Claude) commonly make when generating Salesforce Apex code. These patterns are critical to validate in generated code.

Source: LLM Mistakes in Apex & LWC - Salesforce Diaries

Table of Contents

1. Non-Existent Methods
2. Java Types Instead of Apex Types
3. Map Access Without Null Safety
4. Missing SOQL Fields
5. Recursive Trigger Loops
6. Invalid InvocableVariable Types
7. Missing @JsonAccess Annotations
8. Null Pointer from Missing Checks
9. Incorrect DateTime Methods
10. Collection Initialization Patterns

1. Non-Existent Methods

LLMs often hallucinate methods that don't exist in Apex, borrowing syntax from Java or other languages.

Common Hallucinated Methods

❌ BAD: Hallucinated Datetime Method

// LLM generates this - DOES NOT EXIST
Datetime future = Datetime.now().addMilliseconds(500);

✅ GOOD: Correct Apex Pattern

// Apex has no millisecond precision - use seconds
Datetime future = Datetime.now().addSeconds(1);

// For sub-second timing, use System.currentTimeMillis()
Long startMs = System.currentTimeMillis();
// ... operation ...
Long elapsedMs = System.currentTimeMillis() - startMs;

❌ BAD: Java Stream Syntax

// LLM generates this - Java streams don't exist in Apex
List<String> names = accounts.stream()
    .map(a -> a.Name)
    .collect(Collectors.toList());

✅ GOOD: Apex Loop Pattern

// Use traditional loops in Apex
List<String> names = new List<String>();
for (Account a : accounts) {
    names.add(a.Name);
}

2. Java Types Instead of Apex Types

LLMs trained on Java code often use Java collection types that don't exist in Apex.

Java Types to Avoid

❌ BAD: Java Collection Types

// LLM generates these - COMPILE ERROR
ArrayList<Account> accounts = new ArrayList<Account>();
HashMap<Id, Contact> contactMap = new HashMap<Id, Contact>();
StringBuilder sb = new StringBuilder();

✅ GOOD: Apex Native Types

// Apex uses these types
List<Account> accounts = new List<Account>();
Map<Id, Contact> contactMap = new Map<Id, Contact>();

// For string concatenation
String result = '';
for (String s : parts) {
    result += s;  // OK for small strings
}

// For large string building
List<String> parts = new List<String>();
parts.add('Part 1');
parts.add('Part 2');
String result = String.join(parts, '');

Detection Rule

REGEX: \b(ArrayList|HashMap|HashSet|StringBuffer|StringBuilder|LinkedList|TreeMap|Vector|Hashtable)\s*<
SEVERITY: CRITICAL
MESSAGE: Java type "{match}" does not exist in Apex. Use Apex native collections.

3. Map Access Without Null Safety

LLMs often use Map.get() without checking if the key exists, causing null pointer exceptions.

❌ BAD: Unsafe Map Access

Map<Id, Account> accountMap = new Map<Id, Account>([SELECT Id, Name FROM Account]);

for (Contact c : contacts) {
    // DANGER: If AccountId not in map, .Name throws NPE
    String accountName = accountMap.get(c.AccountId).Name;
}

✅ GOOD: Safe Map Access (Option 1 - containsKey)

Map<Id, Account> accountMap = new Map<Id, Account>([SELECT Id, Name FROM Account]);

for (Contact c : contacts) {
    if (accountMap.containsKey(c.AccountId)) {
        String accountName = accountMap.get(c.AccountId).Name;
    }
}

✅ GOOD: Safe Map Access (Option 2 - Null Check)

Map<Id, Account> accountMap = new Map<Id, Account>([SELECT Id, Name FROM Account]);

for (Contact c : contacts) {
    Account acc = accountMap.get(c.AccountId);
    if (acc != null) {
        String accountName = acc.Name;
    }
}

✅ GOOD: Safe Map Access (Option 3 - Safe Navigation)

Map<Id, Account> accountMap = new Map<Id, Account>([SELECT Id, Name FROM Account]);

for (Contact c : contacts) {
    // Safe navigation operator (?.) - returns null if key not found
    String accountName = accountMap.get(c.AccountId)?.Name;
    if (accountName != null) {
        // Process
    }
}

✅ GOOD: Safe Map Access (Option 4 - Null Coalescing)

Map<Id, Account> accountMap = new Map<Id, Account>([SELECT Id, Name FROM Account]);

for (Contact c : contacts) {
    // Null coalescing operator (??) for default values
    String accountName = accountMap.get(c.AccountId)?.Name ?? 'Unknown';
}

4. Missing SOQL Fields

LLMs often query fields but then access different fields not in the SELECT clause.

❌ BAD: Accessing Unqueried Fields

// Only querying Id and Name
List<Account> accounts = [SELECT Id, Name FROM Account];

for (Account acc : accounts) {
    // RUNTIME ERROR: Industry was not queried!
    if (acc.Industry == 'Technology') {
        acc.Description = 'Tech company';  // Description also not queried!
    }
}

✅ GOOD: Query All Accessed Fields

// Query all fields that will be accessed
List<Account> accounts = [SELECT Id, Name, Industry, Description FROM Account];

for (Account acc : accounts) {
    if (acc.Industry == 'Technology') {
        acc.Description = 'Tech company';
    }
}

❌ BAD: Missing Relationship Fields

// Missing Account.Name in query
List<Contact> contacts = [SELECT Id, Name, AccountId FROM Contact];

for (Contact c : contacts) {
    // RUNTIME ERROR: Account.Name not queried
    System.debug('Account: ' + c.Account.Name);
}

✅ GOOD: Include Relationship Fields

// Include relationship fields using dot notation
List<Contact> contacts = [SELECT Id, Name, AccountId, Account.Name FROM Contact];

for (Contact c : contacts) {
    System.debug('Account: ' + c.Account.Name);  // Works!
}

Validation Checklist

Before running code, verify:

1. All fields accessed in if statements are queried
2. All fields accessed in assignments are queried
3. All relationship fields (e.g., Account.Name) are in SELECT
4. Parent relationship uses . notation in query (e.g., Contact.Account.Name)

5. Recursive Trigger Loops

LLMs often forget to add recursion prevention in triggers, causing infinite loops.

❌ BAD: No Recursion Prevention

// Trigger that updates related records
trigger AccountTrigger on Account (after update) {
    List<Contact> contactsToUpdate = new List<Contact>();

    for (Account acc : Trigger.new) {
        // This update might trigger another trigger, which might update Account...
        for (Contact c : [SELECT Id FROM Contact WHERE AccountId = :acc.Id]) {
            c.MailingCity = acc.BillingCity;
            contactsToUpdate.add(c);
        }
    }

    update contactsToUpdate;  // Could cause recursion!
}

✅ GOOD: Static Flag Pattern

// TriggerHelper.cls
public class TriggerHelper {
    private static Boolean isFirstRun = true;

    public static Boolean isFirstRun() {
        if (isFirstRun) {
            isFirstRun = false;
            return true;
        }
        return false;
    }

    public static void reset() {
        isFirstRun = true;
    }
}

// AccountTrigger.trigger
trigger AccountTrigger on Account (after update) {
    if (!TriggerHelper.isFirstRun()) {
        return;  // Skip on recursive calls
    }

    // ... trigger logic ...
}

✅ BETTER: Set-Based Recursion Control

// TriggerRecursionHandler.cls
public class TriggerRecursionHandler {
    private static Set<Id> processedIds = new Set<Id>();

    public static Boolean hasProcessed(Id recordId) {
        return processedIds.contains(recordId);
    }

    public static void markProcessed(Id recordId) {
        processedIds.add(recordId);
    }

    public static void markProcessed(Set<Id> recordIds) {
        processedIds.addAll(recordIds);
    }
}

// In trigger handler
for (Account acc : Trigger.new) {
    if (TriggerRecursionHandler.hasProcessed(acc.Id)) {
        continue;
    }
    TriggerRecursionHandler.markProcessed(acc.Id);
    // Process record...
}

✅ BEST: Trigger Actions Framework

// Use TAF for built-in recursion control via metadata
// See: references/trigger-actions-framework.md

6. Invalid InvocableVariable Types

LLMs often use unsupported types in @InvocableVariable annotations for Flow/Process Builder integration.

Supported InvocableVariable Types

Unsupported Types

❌ BAD: Unsupported InvocableVariable Types

public class FlowInput {
    @InvocableVariable
    public Map<String, String> options;  // NOT SUPPORTED!

    @InvocableVariable
    public Set<Id> recordIds;  // NOT SUPPORTED!

    @InvocableVariable
    public Blob fileContent;  // NOT SUPPORTED!
}

✅ GOOD: Supported Types with Wrapper Pattern

public class FlowInput {
    @InvocableVariable(label='Record IDs' description='Comma-separated IDs')
    public List<Id> recordIds;  // List is supported

    @InvocableVariable(label='Options JSON' description='JSON string of options')
    public String optionsJson;  // Serialize Map to JSON string

    @InvocableVariable(label='File Content' description='Base64 encoded content')
    public String fileContentBase64;  // Base64 encode Blob
}

// In your method, deserialize as needed
public static void process(List<FlowInput> inputs) {
    for (FlowInput input : inputs) {
        Map<String, String> options = (Map<String, String>)JSON.deserialize(
            input.optionsJson,
            Map<String, String>.class
        );

        Blob fileContent = EncodingUtil.base64Decode(input.fileContentBase64);
    }
}

7. Missing @JsonAccess Annotations

When using JSON.serialize() / JSON.deserialize() with inner classes or non-public classes, LLMs forget the @JsonAccess annotation required since API version 49.0.

❌ BAD: Missing JsonAccess

public class AccountService {
    // Inner class without @JsonAccess - JSON.serialize() fails silently
    private class AccountWrapper {
        public String name;
        public String industry;
    }

    public static String getAccountsJson() {
        List<AccountWrapper> wrappers = new List<AccountWrapper>();
        // ... populate ...
        return JSON.serialize(wrappers);  // Returns "[]" or throws error!
    }
}

✅ GOOD: With JsonAccess Annotation

public class AccountService {
    @JsonAccess(serializable='always' deserializable='always')
    private class AccountWrapper {
        public String name;
        public String industry;
    }

    public static String getAccountsJson() {
        List<AccountWrapper> wrappers = new List<AccountWrapper>();
        // ... populate ...
        return JSON.serialize(wrappers);  // Works correctly!
    }
}

When @JsonAccess is Required

8. Null Pointer from Missing Checks

LLMs often chain method calls without null safety, leading to null pointer exceptions.

❌ BAD: Chained Calls Without Null Checks

// Any of these could be null!
String city = [SELECT Id, Account.BillingAddress FROM Contact LIMIT 1]
    .Account
    .BillingAddress
    .getCity();

✅ GOOD: Safe Navigation Operator

// Use ?. for safe navigation
Contact c = [SELECT Id, Account.BillingCity FROM Contact LIMIT 1];
String city = c?.Account?.BillingCity;

// With default value
String city = c?.Account?.BillingCity ?? 'Unknown';

✅ GOOD: Explicit Null Checks

Contact c = [SELECT Id, Account.BillingCity FROM Contact LIMIT 1];

String city = 'Unknown';
if (c != null && c.Account != null && c.Account.BillingCity != null) {
    city = c.Account.BillingCity;
}

9. Incorrect DateTime Methods

LLMs confuse Date and DateTime methods, which have different APIs.

Date vs DateTime Method Confusion

❌ BAD: Mixing Date/DateTime Methods

// Date doesn't have addHours!
Date d = Date.today();
Date future = d.addHours(5);  // COMPILE ERROR

// DateTime doesn't have a static today()!
DateTime now = DateTime.today();  // COMPILE ERROR

✅ GOOD: Correct Method Usage

// For Date operations
Date d = Date.today();
Date future = d.addDays(5);

// For DateTime operations
DateTime now = DateTime.now();
DateTime future = now.addHours(5);

// Converting between Date and DateTime
Date d = Date.today();
DateTime dt = DateTime.newInstance(d, Time.newInstance(0, 0, 0, 0));

DateTime dt = DateTime.now();
Date d = dt.date();

10. Collection Initialization Patterns

LLMs sometimes use incorrect patterns for initializing collections from SOQL or other collections.

❌ BAD: Incorrect Map Initialization

// This doesn't work - can't construct Map from SOQL directly with fields
Map<Id, String> nameMap = new Map<Id, String>(
    [SELECT Id, Name FROM Account]
);  // COMPILE ERROR - wrong constructor

✅ GOOD: Correct Map Initialization

// Map<Id, SObject> works directly with SOQL
Map<Id, Account> accountMap = new Map<Id, Account>(
    [SELECT Id, Name FROM Account]
);

// For Map<Id, SpecificField>, use a loop
Map<Id, String> nameMap = new Map<Id, String>();
for (Account acc : [SELECT Id, Name FROM Account]) {
    nameMap.put(acc.Id, acc.Name);
}

❌ BAD: List to Set Conversion

// Can't directly convert List to Set in constructor
List<Id> idList = new List<Id>{'001...', '001...'};
Set<Id> idSet = new Set<Id>(idList);  // Actually this DOES work in Apex!

✅ GOOD: Collection Conversions

// List to Set - this works!
List<Id> idList = new List<Id>{'001...', '001...'};
Set<Id> idSet = new Set<Id>(idList);

// Set to List
Set<Id> idSet = new Set<Id>{'001...', '001...'};
List<Id> idList = new List<Id>(idSet);

// Map keys to Set
Map<Id, Account> accountMap = new Map<Id, Account>([SELECT Id FROM Account]);
Set<Id> accountIds = accountMap.keySet();

// Map values to List
List<Account> accounts = accountMap.values();

Quick Reference: LLM Validation Checklist

Before accepting LLM-generated Apex code, verify:

Methods & Types

• No Java collection types (ArrayList, HashMap, etc.)
• No hallucinated methods (addMilliseconds, stream(), etc.)
• Correct Date vs DateTime methods

Null Safety

• Map.get() has null check or uses containsKey()
• Chained method calls use safe navigation (?.)
• SOQL results checked before accessing

SOQL

• All accessed fields are in SELECT clause
• Relationship fields use dot notation in query
• Parent records accessed safely

Flow Integration

• InvocableVariable uses supported types
• No Map/Set in @InvocableVariable
• @JsonAccess on inner classes if serialized

Triggers

• Recursion prevention mechanism in place
• Static flag or processed ID tracking

Detection Script

Add this validation to your CI/CD pipeline:

# detect_llm_patterns.py
import re

JAVA_TYPES = [
    r'\bArrayList\s*<',
    r'\bHashMap\s*<',
    r'\bHashSet\s*<',
    r'\bStringBuffer\b',
    r'\bStringBuilder\b',
    r'\bLinkedList\s*<',
    r'\bTreeMap\s*<',
]

HALLUCINATED_METHODS = [
    r'\.addMilliseconds\s*\(',
    r'\.stream\s*\(\)',
    r'\.getOrDefault\s*\(',
    r'DateTime\.today\s*\(\)',
]

def validate_apex(content):
    issues = []

    for pattern in JAVA_TYPES:
        if re.search(pattern, content):
            issues.append(f"Java type detected: {pattern}")

    for pattern in HALLUCINATED_METHODS:
        if re.search(pattern, content):
            issues.append(f"Non-existent method: {pattern}")

    return issues

Reference

• Existing Anti-Patterns: See references/anti-patterns.md for traditional Apex anti-patterns
• Best Practices: See references/best-practices.md for correct patterns
• Source: Salesforce Diaries - LLM Mistakes