Prevent duplicate records in custom object

Question

I have a custom object. There are combination of fields like month_c,Project_c,contact_c and role_c which determine the record as unique.

I can write a trigger on before insert to check if there are any records with the same combination already existing. The question i wanted to ask was

how can i make the insertion stop. once i find there is already an record then it should just not insert the record. it doesnt need to throw / show an error.

Thanks

Prady

Answer 1

Although others have answered this with better solutions (generally non-code solutions are more flexible for the end users of the system), the answer to stop a particular record from being inserted is to add an error to a field on that record.

For instance, if I was inserting accounts I might have something like this:

for(Account sAcct : trigger.new)
{
    if(sAcct.Name == 'DeniedAccount')
    {
        sAcct.Name.addError('This is a denied account.');
    }
}

Another alternative is to create a class extending Exception, and then throw a new instance of that exception class, this will prevent all of the records passed to the trigger from being processed as opposed to specific records.