Lesson: 29 | Prevent users to create an opportunity with an existing name

I am a User.

WHEN I want to create a New Opportunity AND there is already an Opportunity with the same name

THEN a validation error message should prevent me from doing this change.

ERROR MESSAGE: There is an Opportunity with the same Name. Try another name

trigger OppTrigger on Opportunity (before insert) {
    List<Opportunity> oppList =[SELECT Id, Name FROM Opportunity WHERE Name =:Trigger.new[0].Name];
    if(oppList.size()!=0){
        Trigger.new[0].Name.addError('There is an Opportunity with the same Name. Try another name');
    }
}