Lesson: 17 | Unique Email

Apex Trigger

trigger ContactTrigger on Contact (before insert) {
    
    Set<String> oldEmails = new Set<String>();
    
    for(Contact con : [SELECT id, Email FROM Contact]){
        oldEmails.add(con.Email);
    }
    for(Contact con : Trigger.new){
        if(oldEmails.contains(con.email)){
            con.email.addError('An account with the same name is already exists.');
        }
    }
    
}