sqlalchemy-orm-query-querycontext.markdown

title: sqlalchemy.orm.query QueryContext Example Code category: page slug: sqlalchemy-orm-query-querycontext-examples sortorder: 500031089 toc: False sidebartitle: sqlalchemy.orm.query QueryContext meta: Example code for understanding how to use the QueryContext class from the sqlalchemy.orm.query module of the SQLAlchemy project.

QueryContext is a class within the sqlalchemy.orm.query module of the SQLAlchemy project.

Query is another callable from the sqlalchemy.orm.query package with code examples.

Example 1 from graphene-sqlalchemy

graphene-sqlalchemy (project documentation and PyPI package information) is a SQLAlchemy integration for Graphene, which makes it easier to build GraphQL-based APIs into Python web applications. The package allows you to subclass SQLAlchemy classes and build queries around them with custom code to match the backend queries with the GraphQL-based request queries. The project is provided as open source under the MIT license.

graphene-sqlalchemy / graphene_sqlalchemy / batching.py

# batching.py
import sqlalchemy
from promise import dataloader, promise
from sqlalchemy.orm import Session, strategies
~~from sqlalchemy.orm.query import QueryContext


def get_batch_resolver(relationship_prop):

    selectin_loader = strategies.SelectInLoader(relationship_prop, (('lazy', 'selectin'),))

    class RelationshipLoader(dataloader.DataLoader):
        cache = False

        def batch_load_fn(self, parents):  # pylint: disable=method-hidden
            child_mapper = relationship_prop.mapper
            parent_mapper = relationship_prop.parent
            session = Session.object_session(parents[0])

            for parent in parents:
                assert session is Session.object_session(parent)
                assert parent not in session.dirty

            states = [(sqlalchemy.inspect(parent), True) for parent in parents]

~~            query_context = QueryContext(session.query(parent_mapper.entity))

            selectin_loader._load_for_path(
                query_context,
                parent_mapper._path_registry,
                states,
                None,
                child_mapper,
            )

            return promise.Promise.resolve([getattr(parent, relationship_prop.key) for parent in parents])

    loader = RelationshipLoader()

    def resolve(root, info, **args):
        return loader.load(root)

    return resolve



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