How to run the getRole command using pymongo? - mongodb

Question

I want to check whether a role exists in a mongodb, before I create a new one . I tried to do it the following way:
result = self.client[database].command("getRole", name=app_name)
Unfortunately I get the following error:
msg = msg or "%s"
raise OperationFailure(msg % errmsg, code, response)
pymongo.errors.OperationFailure: no such command: 'getRole', bad cmd: '{ getRole: 1, name: "test" }'
I am referring to this database command: https://docs.mongodb.com/manual/reference/method/db.getRole/
For createRole I can execute the command: https://docs.mongodb.com/manual/reference/method/db.createRole/#db.createRole

Answer 1

Shell methods db.* are different from Database commands.
Using the roleInfo command you can get information for a particular role.
db.command({
'rolesInfo': {'role': 'noremove','db': 'test'},
'showPrivileges': True, 'showBuiltinRoles': True
})
The above command returns a result in this form when there is a matching role:
{'ok': 1.0,
'roles': [{'db': 'test',
'inheritedPrivileges': [{'actions': ['find', 'insert', 'update'],
'resource': {'collection': 'test', 'db': 'test'}}],
'inheritedRoles': [],
'isBuiltin': False,
'privileges': [{'actions': ['find', 'insert', 'update'],
'resource': {'collection': 'test', 'db': 'test'}}],
'role': 'noremove',
'roles': []}]}
When there is no matching role, you get this result:
{'ok': 1.0, 'roles': []}
Checking that a role exists falls to checking for the length of the "roles" list in the returned result as follow:
noremove_role = db.command({
'rolesInfo': {'role': 'noremove','db': 'test'},
'showPrivileges': True, 'showBuiltinRoles': True
})
if not len(noremove_role['roles']):
# create role
pass
Is there a better way?
Yes, in keeping with ask forgiveness not permission philosophy, create the role and handle the resulting exception from trying to add an existing role.
from pymongo.errors import DuplicateKeyError
import logging
logger = logging.getLogger()
try:
db.command(
'createRole', 'noremove',
privileges=[{
'actions': ['insert', 'update', 'find'],
'resource': {'db': 'test', 'collection': 'test'}
}],
roles=[])
except DuplicateKeyError:
logger.error('Role already exists.')
pass