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53 lines
2.2 KiB
ReStructuredText
53 lines
2.2 KiB
ReStructuredText
Implementing custom validators
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==============================
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GraphQL uses query validators to check if Query AST is valid and can be executed. Every GraphQL server implements standard query validators.
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For example, a validator tests if a queried field exists on queried type, making the query fail with a "Cannot query field on type" error if it does not.
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If you need more complex validation than presented before, you can implement your own query validators.
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Implementing your custom validators
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-----------------------------------
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All custom query validators should extend the `ValidationRule`_ base class importable from the ``graphql.validation.rules`` module.
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Query validators are `Visitor`_ classes.
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Your custom validator should implement some methods of
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In order to perform validation, your validator class should define some one or more of ``enter_*`` or ``leave_*`` methods.
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Foreach methods, you will receive a node object to test:
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- You can now choose to raise an error by calling ``report_error`` method with an instance of GraphQLError describing the failure reason.
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- Or you can continue the parsing by returning ``None``.
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Example
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-------
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Here is an example query validator that only allows queries fields with a name of even length.
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.. code:: python
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from graphql import GraphQLError
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from graphql.language import FieldNode
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from graphql.validation import ValidationRule
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class MyCustomValidationRule(ValidationRule):
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def enter_field(self, node: FieldNode, *_args):
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if len(node.name.value) % 2 == 0:
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# Here the query length is even, so we allow it.
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return
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else:
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# Here the query length is odd, so we don't want to allow it.
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# Calling self.report_error will make the query fail with the error message.
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self.report_error(
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GraphQLError(
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f"Cannot query '{field_name}': length is odd.", node,
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)
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)
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.. _ValidationRule: https://github.com/graphql-python/graphql-core/blob/v3.0.5/src/graphql/validation/rules/__init__.py#L37
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.. _Visitor: https://github.com/graphql-python/graphql-core/blob/d90bf9902ca1639365639d5632861d1e18d672a9/src/graphql/language/visitor.py#L111
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