def _add_constraints(self, relation):
names = []<EOL>expression = relation.expression<EOL>for value_set in expression.value_sets():<EOL><INDENT>name = next(self._constr_names)<EOL>self._p.addConstr(<EOL>self._grb_expr_from_value_set(value_set),<EOL>self.CONSTR_SENSE_MAP[relation.sense],<EOL>-float(expression.offset), name)<EOL>names.append(name)<EOL><DEDENT>self._p.update()<EOL>return names<EOL>
Add the given relation as one or more constraints.

        Return a list of the names of the constraints added.