mirror of
https://github.com/graphql-python/graphene.git
synced 2025-02-02 20:54:16 +03:00
42 lines
2.1 KiB
ReStructuredText
42 lines
2.1 KiB
ReStructuredText
Implementing custom validators
|
|
==============================
|
|
|
|
GraphQL uses query validators to check if Query AST is valid and can be executed. Every GraphQL server implements
|
|
standard query validators. For example, there is an validator that tests if queried field exists on queried type, that
|
|
makes query fail with "Cannot query field on type" error if it doesn't.
|
|
|
|
If you need more complex validation than presented before, you can implement your own query validators. All custom query
|
|
validators should extend the `ValidationRule`_ base class importable from the ``graphql.validation.rules`` module. Query
|
|
validators are visitor classes. They are instantiated at the time of query validation with one required argument
|
|
(context: ASTValidationContext). In order to perform validation, your validator class should define one or more of
|
|
``enter_*`` and ``leave_*`` methods. For possible enter/leave items as well as details on function documentation, please
|
|
see contents of the visitor module. To make validation fail, you should call validator's report_error method with the
|
|
instance of GraphQLError describing failure reason.
|
|
|
|
Implementing your custom validators
|
|
-----------------------------------
|
|
|
|
Here is an example query validator that only allows queries fields with a name of even length.
|
|
|
|
.. code:: python
|
|
|
|
from graphql import GraphQLError
|
|
from graphql.language import FieldNode
|
|
from graphql.validation import ValidationRule
|
|
|
|
|
|
class MyCustomValidationRule(ValidationRule):
|
|
def enter_field(self, node: FieldNode, *_args):
|
|
if len(node.name.value) % 2 == 0:
|
|
# Here the query length is even, so we allow it.
|
|
return
|
|
else:
|
|
# Here the query length is odd, so we don't want to allow it.
|
|
# Calling self.report_error will make the query fail with the error message.
|
|
self.report_error(
|
|
GraphQLError(
|
|
f"Cannot query '{field_name}': length is odd.", node,
|
|
)
|
|
)
|
|
|
|
.. _ValidationRule: https://github.com/graphql-python/graphql-core/blob/v3.0.5/src/graphql/validation/rules/__init__.py#L37 |