How to Block Recursion in Triggers?

Question:

How can recursion be effectively blocked in generic trigger handlers that handle all TriggerOperation types for arbitrary SObject types? Specifically, what are robust strategies to block recursion while allowing valid updates, handling partial updates, and avoiding side effects like blocking retries or workflows?

Answer

A proper strategy for recursion blocking depends on the context and requirements of your implementation. Here are a few approaches, along with considerations for their use:

1. Block During Known Recursive Updates Only

This pattern involves using a static Boolean flag to block recursion only when updates known to cause recursion are being performed. Here’s an example:

public class AccountTriggerHandler {
    static Boolean isInAccountUpdate = false;

    public static void afterUpdate(Account[] oldValues, Account[] newValues) {
        if (!isInAccountUpdate) {
            if (shouldDoUpdate()) {
                isInAccountUpdate = true; // Block further recursion
                updateRecords(oldValues, newValues);
                isInAccountUpdate = false; // Unblock after updates
            }
        }
    }
}

This approach works well for simple cases where recursive updates can be identified and controlled. However, it might not suffice for more complex scenarios with multiple operations or partial updates.

2. Use “Rising Edge” Triggers

A rising edge trigger processes only records that have undergone meaningful changes, minimizing the need for recursion blocking. Here’s an example:

public static void afterUpdate(Account[] oldValues, Account[] newValues) {
    Account[] oldChanges = new Account[0], newChanges = new Account[0];
    for (Integer i = 0; i < newValues.size(); i++) {
        if (recordChanged(oldValues[i], newValues[i])) {
            oldChanges.add(oldValues[i]);
            newChanges.add(newValues[i]);
        }
    }
    processChangedRecords(oldChanges, newChanges);
}

This pattern reduces the risk of recursion without additional variables, as it ensures updates are processed only when necessary. It’s a more declarative approach to handling changes.

3. Use a Set to Track Processed Records

For cases involving multiple records of the same type or updates that span different trigger contexts, a Set<Id> can be used to track which records have already been processed. The key is to reset this set at the end of the trigger to avoid blocking valid updates or retries.

public class AccountTriggerHandler {
    static Set<Id> accountIds = new Set<Id>();

    public static void afterUpdate(Account[] oldValues, Account[] newValues, Set<Id> accountIdSet) {
        if (accountIds.containsAll(accountIdSet)) {
            return; // Skip already processed records
        }
        accountIds.addAll(accountIdSet); // Mark records as processed
        doMainLogicHere();
        accountIds.removeAll(accountIdSet); // Reset at the end of the trigger
    }
}

This method ensures that partial updates, retries, or updates involving workflows and approval processes are handled without side effects. Always clear the set when the trigger completes to maintain flexibility and reliability.

Considerations and Best Practices:

1. Always reset recursion-blocking flags or sets at the end of the trigger context. Failing to do so can block valid updates or cause unintended behavior in workflows and tests.
2. Minimize the “lock time” during which recursion is blocked. Locking for longer than necessary can interfere with retries and chained operations.
3. Combine patterns as needed. A single static Boolean may suffice for simple cases, while more complex scenarios might require a combination of rising edge triggers and record-tracking sets.
4. Ensure that your implementation supports partial updates. For example, if a batch operation processes some records but fails for others, your handler should correctly handle retries.

There is no one-size-fits-all solution for recursion blocking in generic trigger handlers. Depending on the complexity of your triggers and the business logic, you may use simple Boolean flags, rising edge triggers, or record-tracking sets. A robust implementation often combines these strategies to balance performance, correctness, and maintainability.

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