I tried following this reference and this is now my domain's code:

class SnbrActVector {

    long nid
    String term
    double weight

    static mapping = {
        version false
        nid index:'Nid_Idx'
    }

    static constraints = {
        term(blank:false)
    }
}

What I want is to do is to add an index key for 'nid' column. I dropped the existing table and run the app again so the table is then recreated. However, when i check for list of indices, I can't see a 'Nid_Idx', only available is 'PRIMARY'. Do I have to manually create the index and name it 'Nid_idx in my mysql database?

Thanks.