How to check referential integrity in Cerberus?

Question

Consider the following Cerberus schema:

{
  'employee': {
    'type': 'list',
    'schema': {
      'type': 'dict',
      'schema': {
        'id': {'required': True, 'type': 'integer'},
        'name': {'required': True, 'type': 'string'}
      }
    }
  },
  'ceo-employee-id': {'required': True, 'type': 'integer'}
}

1) How can I validate that the ceo-employee-id matches one of the id values in the employee list? (Referential integrity)

2) How can I validate that each id in the employee list is unique (i.e. no duplicate employee ids)?

I realize I can do this at run-time after validating and parsing the config as suggested by @rafael below. I am wondering if I can do it with the Cerberus validation features.

score 3 · Accepted Answer · answered May 04 '19 at 18:18

You'll need to make use of a custom validator that implements check_with methods, use the document property in these, and amend your schema to include these:

from cerberus import Validator


class CustomValidator(Validator):
    def _check_with_ceo_employee(self, field, value):
        if value not in (x["id"] for x in self.document["employee"]):
            self._error(field, "ID is missing in employee list.")

    def _check_with_employee_id_uniqueness(self, field, value):
        all_ids = [x["id"] for x in self.document["employee"]]
        if len(all_ids) != len(set(all_ids)):
            self._error(field, "Employee IDs are not unique.")


validator = CustomValidator({
    'employee': {
        'type': 'list',
        'schema': {
            'type': 'dict',
            'schema': {
                'id': {'required': True, 'type': 'integer'},
                'name': {'required': True, 'type': 'string'}
             },
        },
        'check_with': 'employee_id_uniqueness'
    },
    'ceo-employee-id': {'required': True, 'type': 'integer', 'check_with': 'ceo_employee'}
})

The referenced document contains hints on all the parts used here.

(I apologize for any indentation error that might have slipped into the example.)

score 0 · Answer 2 · answered Apr 21 '19 at 14:13

assuming that you already have validated the schema of your json you can easily check your two conditions like this. Let doc be your json document.

employee_ids = [employee['id'] for employee in doc['employee']]
ceo_employee_id =  doc['ceo-employee-id']

1) How can I validate that the ceo-employee-id matches one of the id values in the employee list? (Referential integrity)

ceo_id_exists_in_employees = any([employee_id == ceo_employee_id for employee_id in employee_ids])

2) How can I validate that each id in the employee list is unique (i.e. no duplicate employee ids)?

employee_id_is_unique = len(set(employee_ids)) == len(employee_ids)

3) Assert that both values are True

if ceo_id_exists_in_employees and employee_id_is_unique:
    print('passed')
else:
    print('failed')

Yes, I understand I can do this at run-time after validating and parsing the config. I was wondering if I can do it with the Cerberus validation features. I will add this clarification to the question. — Bruno Rijsman, Apr 21 '19 at 14:17

How to check referential integrity in Cerberus?

2 Answers2