How to implement proper locking in APEX?

Question

I'm trying to implement locking in sake of not having duplicates. The problem is it works only with this line System.debug(LoggingLevel.DEBUG, 'duplicateCallLog.size() == 0 - '+ duplicateCallLog.size());. It sounds like System.debug call guarantees that result of insert will be available in other instances of controllers. Is there any procedure in APEX aka commit or saveChanges that grants data in database? Or there any other locking patterns in APEX?

   List<CallLog__c> duplicateCallLog = [SELECT Id FROM CallLog__c WHERE SessionID__c = :sessionId ORDER BY CreatedDate DESC NULLS LAST LIMIT 1];
        if(duplicateCallLog.size() == 0)
        {
           System.debug(LoggingLevel.DEBUG, 'duplicateCallLog.size() == 0 - '+ duplicateCallLog.size());
           insert newCallLog;
           newCallLog = [SELECT Id FROM CallLog__c WHERE SessionID__c = :sessionId ORDER BY CreatedDate DESC NULLS LAST LIMIT 1];
           callLogId = newCallLog.Id; 
        }
        else{
           System.debug(LoggingLevel.DEBUG, 'duplicateCallLog.size() != 0 - '+ duplicateCallLog.size());            
           callLogId = null;     
        }                       

Answer 1

I believe what you are looking for is the "FOR UPDATE" keyword on your SOQL calls.

A great resource is Locking Statements

The idea is that you can do the following:

List<Contact> contact = [SELECT Id, Name, Phone FROM Contact WHERE Id IN :idSet FOR UPDATE]

This will allow you to lock the records while you are editing and ensure that no other processes modify the records you pull from the database.