func (s *Storage) PoolsConstraints() *storage.Collection {
	poolConstraintIndex := mgo.Index{Key: []string{"poolexpr", "field"}, Unique: true}
	c := s.Collection("pool_constraints")
	c.EnsureIndex(poolConstraintIndex)
	return c
}
func (s *Storage) PoolsConstraints() *storage.Collection {
	poolConstraintIndex := mgo.Index{Key: []string{"poolexpr", "field"}, Unique: true}
	c := s.Collection("pool_constraints")
	c.EnsureIndex(poolConstraintIndex)
	return c
}
// PoolsConstraints return the pool constraints collection.