Where to place Validation code in an Apex Trigger?

Quite often when i answer questions on Salesforce StackExchange they prompt me to consider future blog posts. This question has been sat on my blog list for a while and i’m finally going to tackle the ‘performing validation in the after‘ comment in this short blog post, so here goes!

Salesforce offers Apex developers two phases within an Apex Trigger, before and after. Most examples i see tend to perform validation code in the before phase of the trigger, even the Salesforce examples show this. However there can be implications with this, that is not at first that obvious. Lets look at an example, first here is my object…

Now the Apex Trigger doing some validation…

trigger LifeTheUniverseAndEverythingTrigger1 on LifeTheUniverseAndEverything__c
   (before insert) {
 
    // Make sure if there is an answer given its always 42!
    for(LifeTheUniverseAndEverything__c record : Trigger.new) {
        if(record.Answer__c!=null && record.Answer__c != 42) {
            record.Answer__c.addError('Answer is not 42!');
        }
    }
}