I have a field and a function for computing this field

'score' : fields. ....
'myfield' : fields.function(_calculate_field,...)

def _calculate_field(self, cr, uid, ids, arg, context=None):
    result = {}
    for i in range(len(ids)):
        item = self.browse(cr, uid, ids[i], context=context)
        if item.data:
            ...
            result[ids[i]] = ...
        else:
            result[ids[i]] = ''
    return result

It work both tree view and form view, it is to heavy because it compute all the records.
I want it just work when I click on 1 record and access to form field, and compute just this record

Sorry for my bad english, thanks for any help