LeadDuplicatePreventer.apex
Force.com Cookbook Sample Code
Chapter 4: Best Practices for Writing Apex - Bulk Processing Records in a Trigger
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This Apex trigger is a good example of how to write a trigger that processes records in bulk. Instead of looping over individual records in the Trigger.old or Trigger.new lists, it uses maps to organize records based on their ID or another identifying field, and sets to isolate distinct records.
trigger leadDuplicatePreventer on Lead (before insert, before update) {
Map<String, Lead> leadMap = new Map<String, Lead>();
for (Lead lead : System.Trigger.new) {
// Make sure we don't treat an email address that
// isn't changing during an update as a duplicate.
if ((lead.Email != null) && (System.Trigger.isInsert || (lead.Email != System.Trigger.oldMap.get(lead.Id).Email))) {
// Make sure another new lead isn't also a duplicate
if (leadMap.containsKey(lead.Email)) {
lead.Email.addError('Another new lead has the same email address.');
} else {
leadMap.put(lead.Email, lead);
}
}
}
// Using a single database query, find all the leads in
// the database that have the same email address as any
// of the leads being inserted or updated.
for (Lead lead : [SELECT Email FROM Lead WHERE Email IN :leadMap.KeySet()]) {
Lead newLead = leadMap.get(lead.Email);
newLead.Email.addError('A lead with this email address already exists.');
}
}
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