Custom Logging, @Future, Transaction Control

Question

I have a similar question to these two: Custom Logging and Future Methods Custom Exception Handling & Logging

But my question this time is: can I put the @Future annotation on the Logger Class? Why would this not allow me to process DML even if an exception is thrown?

Scenario: I have a custom Logger class that inserts a custom record with a error message. The logger class is called at the end of every catch statement. The only way for the Logger class to insert a new record is if we do not re-throw the caught exception. I do not want to do this because if there is an exception, this indicates something is broken which should halt the entire process. This leading me to never be able to insert a new Log error record.

My thought is: if the logger method runs in the future, is it possible for the process to run, all exceptions are thrown, the process is halted, AND THEN my log message DML happens outside of the transaction?

For example:

global with sharing class NFLogger {
private enum LogLevel {Error, Info}

@Future
public static void logError(String tags, String errorMessage){
    logMessage(logLevel.Error, tags, errorMessage, null);
}

@Future
public static void logError(String tags, String errorMessage, String ex){
    logMessage(logLevel.Error, tags, errorMessage, ex);
}

@Future
public static void logInfo(String tags, String infoMessage){
    logMessage(logLevel.Info, tags, infoMessage, null);
}

private static void logMessage(LogLevel level, String tags, String message, String ex){
    try {
        system.debug('Level = ' + level + ', tags = ' + tags + ', message = ' + message + ', system exception = ' + ex);
        LogMessage__c newMessage = new LogMessage__c(level__c = level.name(), tags__c = tags, message__c = message, exception__c = ex);
        insert newMessage;
    }
    catch (Exception e){
        //intentionally "we suppress" any exception
        //we need to guarantee that logMessage will never throw any exceptions
        system.debug('in the catch of NFLogger');
    }
}
}

APEX:

    ...
    try{
        TokenGenerator tg = new TokenGenerator();
        String tokenizedPayload = tg.getTokenizedPayloadForSingleLead(pLead, nfId); //WEBSERVICE
        return new pageReference('/apex/DLPEmailLinkUpdateSvc?id='+pLead+'&tokencred='+tokenizedPayload+'&data='+data+'&ptype=lead');
    } catch (Exception ex) {
        Apexpages.addMessages(ex);
        NFLogger.logError('SendDLPRequestLead, tokenizer', 'There has been an error in the SendDLPRequestLead on Lead: ' + pLead, ex);
        throw ex;
    }

Answer 1

Nope, you can't do that with a future method, or with a Queueable, or Batch Apex, because all of those asynchronous invocations are enqueued for execution after the transaction's over - and that enqueueing is rolled back when an unhandled exception is thrown just like DML is.

There is, however, one way you can get those logs out that's rollback-proof: Platform Events.

Unlike custom objects, platform events aren’t processed within database transactions in the Lightning platform. As a result, published platform events can’t be rolled back.

If what you really want is to throw an exception and roll back the transaction, but also persist some logging information, publish a Platform Event in your handler. Then, the trigger associated with your Platform Event can do the work needed to persist the log details into the database. That persisting takes place in a separate transaction, as the Automated Process user, and is not subject to the rollback of your original transaction.

That said, I'm not convinced that letting an unhandled exception propagate is the correct choice in the situations you're showing in your code. In backend code, yes. But - acknowledging that there are many schools of thought on exceptions across the software development world - I don't like unhandled exceptions in my UI code (Visualforce and Lightning controllers).

The user experience is not ideal in those cases, so I prefer to catch and handle them by presenting a user-friendly message. In Lightning, however, that does entail re-raising an AuraHandledException.

Answer 2

For your question:

is it possible for the process to run, all exceptions are thrown, the process is halted, AND THEN my log message DML happens outside of the transaction?

One of the approaches you can address this scenario is using try-catch-finally as finally block is always guaranteed to be executed as long as it's not an uncatchable exception. So your exceptions are handled, and only then you log the message by keeping your flow synchronous in nature without getting into complexities of handling this asynchronously.

Code in the finally block always executes regardless of whether an exception was thrown or the type of exception that was thrown. Because the finally block always executes, use it for cleanup code, such as for freeing up resources.

Sample below.

Based on a quick test, this approach will work if you are handling the exception in the catch block and not rethrowing it.

Boolean isException = false;
Exception myEx;
try {
....
} catch (Exception e) {
    isException = true;
    myEx = e;
    // handle exception
} finally {
    // verify if exception occurred, then take the call
    if(isException) {
        // log messages
    }
}