Graphene Python class doesn't recognize self

Question

I have the following Python module that implements Graphene.

import graphene
import json
import psycopg2

connection = psycopg2.connect(user='postgres', password='xxxxx', host='127.0.0.1', port='5432', database='xxxx')
cursor = connection.cursor()

class Entity(graphene.ObjectType):
    name = graphene.String()

class Query(graphene.ObjectType):
    entity_relationships = graphene.List(Entity, entity=graphene.String())
    postgresql_version = graphene.String
    path = graphene.String(name=graphene.String(), path=graphene.String(), accumulate=graphene.String(), depth=graphene.Int())

    def get_foreign_relationships(self, entity):
        cursor.execute('''
            SELECT 
                tc.table_schema, tc.constraint_name, tc.table_name, kcu.column_name, ccu.table_schema AS foreign_table_schema, ccu.table_name AS foreign_table_name, ccu.column_name AS foreign_column_name 
            FROM information_schema.table_constraints AS tc 
            JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_name
            AND tc.table_schema = kcu.table_schema
            JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name
            AND ccu.table_schema = tc.table_schema
            WHERE tc.constraint_type = 'FOREIGN KEY' AND tc.table_name='{}';'''.format(entity))
        result = cursor.fetchall()
        result_array = []
        
        for record in result:
            new_entity = Entity(name=record[5])
            result_array.append(new_entity)

        return result_array

    def is_relationship(self, referencing, referenced):
        foreign_relationships = self.get_foreign_relationships(referencing)

        if referenced in list(map(lambda table: relationship[5], foreign_relationships)):
            return True
        else:
            return False

    def traverse(self, entities, direction):
        for i in range(len(entities)):
            if i > 0 and i < len(entities)-1:
                if not self.is_relationship(entities[i], entities[i-1]):
                    raise "entity {} has no relation with entity {}".format(entities[i], entities[i-1])

        return True

    def validate_path(self, path):
        entities = path.split('/')
        
        self.traverse(entities)

        return True

    def resolve_path(self, info, name, path, accumulate, depth):
        if self.validate_path(path):
            return "Éste método regresará los datos anidados para el camino '{}'".format(path)

    def resolve_entity_relationships(self, info, entity):
        result_array = self.get_foreign_relationships(entity)

        return result_array

    def resolve_postgresql_version(self, info):
        cursor.execute("SELECT version();")
        record = cursor.fetchone()
        return record

def execute_query(query_to_execute):
    queries = {
        'postgresqlVersion': '''
            {
                postgresqlVersion
            }
        ''',
        'entityRelationships': '''
            {
                entityRelationships (entity: "inventory_productitem") {
                    name
                }
            }
        ''',
        'path': '''
            {
                path(name: "Ventas", path: "inventory_family/inventory_product/inventory_sale", accumulate: "_calculate(amount*price)", depth: 1)
            }
        '''
    }

    schema = graphene.Schema(query=Query)

    result = schema.execute(queries[query_to_execute])

    dict_result = dict(result.data.items())
    print(json.dumps(dict_result, indent=2))

execute_query('path')

The problem is that resolvers that call other methods of the class raise this error:

Traceback (most recent call last):
  File "/Users/hugovillalobos/Documents/Code/agrowareproject/backend/AgrowareVenv/lib/python3.7/site-packages/graphql/execution/executor.py", line 452, in resolve_or_error
    return executor.execute(resolve_fn, source, info, **args)
  File "/Users/hugovillalobos/Documents/Code/agrowareproject/backend/AgrowareVenv/lib/python3.7/site-packages/graphql/execution/executors/sync.py", line 16, in execute
    return fn(*args, **kwargs)
  File "query.py", line 59, in resolve_path
    if self.validate_path(path):
graphql.error.located_error.GraphQLLocatedError: 'NoneType' object has no attribute 'validate_path'

The line that rises the error is: if self.validate_path(path):

I don't know why, if method validate_path() is in the same class that the method that calls it.

Answer 1

This is because Graphene considering all resolver methods are staticmethods

From the doc,

Sometimes this argument will be named self in Graphene code, but this can be misleading due to Implicit staticmethod while executing queries in Graphene.

So, you must rearrange your code as follows,

def validate_path(path):
    # do something
    return True  # ot False depends on your evaluation


class Query(graphene.ObjectType):
    path = graphene.String(
        name=graphene.String(),
        path=graphene.String(),
        accumulate=graphene.String(),
        depth=graphene.Int()
    )

    @staticmethod
    def resolve_path(parent, info, name, path, accumulate, depth):
        if validate_path(path):
            return "Validated path"
        return "Path Not Valid"