Example for Bulk supported Trigger

  To write bulk safe triggers we need to understand and utilize sets and maps. Sets are used to isolate distinct records, while maps are name-value pairs that hold the query results retrievable by record id. for more details refer the Apex developer guide.

Example:
======

 trigger ChangeColor on Account (before insert, before update)
{
      // create a set of all the unique ownerIds
      Set<id> ownerIds = new Set<id>( );
      for (Account a : Trigger.new)
      {
           ownerIds.add(a.OwnerId);
      }
   
      // query for all the User records for the unique userIds
      Map<id, User> owners = new Map<id, User>([Select Favorite_Color__c from User Where Id in          
                                                      :ownerIds]);
     
      // iterate over the list of records being processed
      for (Account a : Trigger.new)
     {
           a.Owner_Favorite_Color__c = owners.get(a.OwnerId).Favorite_Color__c;
     }
}