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Validating GraphQL Queries
--------------------------
.. currentmodule:: graphql.validation
When executing GraphQL queries, the second step that happens under the hood after
parsing the source code is a validation against the given schema using the rules of the
GraphQL specification. You can also run the validation step manually by calling the
:func:`validate` function, passing the schema and the AST document::
from graphql import parse, validate
errors = validate(schema, parse("""
{
human(id: NEWHOPE) {
name
homePlace
friends
}
}
"""))
As a result, you will get a complete list of all errors that the validators has found.
In this case, we will get the following three validation errors::
[GraphQLError(
'String cannot represent a non string value: NEWHOPE',
locations=[SourceLocation(line=3, column=17)]),
GraphQLError(
"Cannot query field 'homePlace' on type 'Human'."
" Did you mean 'homePlanet'?",
locations=[SourceLocation(line=5, column=9)]),
GraphQLError(
"Field 'friends' of type '[Character]' must have a selection of subfields."
" Did you mean 'friends { ... }'?",
locations=[SourceLocation(line=6, column=9)])]
These rules are available in the :data:`specified_rules` list and implemented in the
:mod:`graphql.validation.rules` subpackage. Instead of the default rules, you can also
use a subset or create custom rules. The rules are based on the :class:`ValidationRule`
class which is based on the :class:`~graphql.language.Visitor` class which provides a
way of walking through an AST document using the visitor pattern.
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