coal/helpers.go
func Contains(list []bson.ObjectId, id bson.ObjectId) bool {
	for _, item := range list {
		if item == id {
			return true
		}
	}

	return false
}
func Contains(list []bson.ObjectId, id bson.ObjectId) bool {
	for _, item := range list {
		if item == id {
			return true
		}
	}

	return false
}
// Contains returns true if a list of object ids contains the specified id.