Trigger Good example with try/catch

gistfile1.txt

trigger CaseTrigger on Case (after insert) {
 
 system.debug('***CaseTrigger begin');

 // In this example trigger we are simply wanting to flag at the Account level
 // that the Account has a Case linked to it, which is a lookup field on Case
 // so we wouldn't be able to do a rollup count.
 // In reality we would also want to track deletes of Cases but that is skipped 
 // for demonstration purposes.
  
 // bulk map of accounts that we need to update
 map<Id, Account> accountsForUpdateMap = new map<Id, Account>();

 // find accounts to update
 for(Case c : trigger.new){
  // if this case is linked to an account and we've not already tagged this account
  if(c.AccountId != null && !accountsForUpdate.containsKey(c.AccountId))
   // add this account to the map
   accountsForUpdate.put(c.AccountId, new Account(Id = c.AccountId, HasACase__c = true));
 }

 // check to see if we need to perform DML
 if(!accountsForUpdate.isEmpty()){
  try{
   // let's do the DML
   update accountsForUpdate.values();
  } catch(dmlexception e){
   // ************ Assume the ACCOUNT update FAILED ***********
   // If DML failed, ends up here
   system.debug('Error updating account: ' + e);

   // Let's force the database to roll-back by adding an error to these records just 
   // like salesforce would normally do.  Our error can be more descriptive though.
            
   // Build a map of Case trigger rows keyed on the Account Id   
   map<id, list<case>> accountIdCaseMap = new map<id, list<case>>();
   for(Case c : trigger.new){
    // if this case is linked to an account that failed
    if(c.AccountId != null)
     // if we already found this account and this is another case, add this 
     // case to that list
     if(accountIdCaseMap.containsKey(c.AccountId))
      accountIdCaseMap.get(c.AccountId).add(c);
     // Add this account id with a new list of Case
     else      
      accountIdCaseMap.put(c.AccountId, new list<case>(c));
   }

   // Loop through the errors and tag the proper cases   
   for ( Integer i = 0; i < e.getNumDml(); i++ ){
    // for this dml error, get the id of the failed account, tag the matching cases.
    for(Case c : accountIdCaseMap.get(e.getDmlId( i )))
     // add an error to this row, which will prevent this row from being updated
     c.addError('Unable to update linked Account record due to an error: ' + 
        e.getDmlMessage( i ));
   }
       
  }

 }

 // If we get this far in code, something may have failed and been caught above, or everything worked.
 system.debug('Potential Success');

 // If anything were to go wrong in the above DML, since we do have a try/catch the server
 // will NOT automatically rollback the changes. But since we have used the .addError method on the 
 // correct trigger rows we have effectively prevented the case inserts.
 // Our error would show to the user on the standard page or to the calling code that fired the trigger.

}