Here is the code:
from sqlalchemy import Column, ForeignKey, Integer, create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship
engine = create_engine('postgresql://postgres@localhost/test_db')
Session = sessionmaker(bind=engine)
session = Session()
Base = declarative_base()
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
class News(Base):
__tablename__ = 'news'
id = Column(Integer, primary_key=True)
comments = relationship('Comment')
class Comment(Base):
__tablename__ = 'comment'
id = Column(Integer, primary_key=True)
news_id = Column(Integer, ForeignKey(News.id))
class CommentRead(Base):
__tablename__ = 'comment_read'
comment_id = Column(Integer, ForeignKey(Comment.id), primary_key=True)
user_id = Column(Integer, ForeignKey(User.id), primary_key=True)
Base.metadata.create_all(engine)
# Initialize data
session.add_all([User(id=1), News(id=2)])
session.commit()
session.add(Comment(id=3, news_id=2))
session.commit()
session.add(CommentRead(comment_id=3, user_id=1))
session.commit()
# Make query
comment_read_query = (
session.query(CommentRead).filter(
CommentRead.comment_id == Comment.id,
CommentRead.user_id == 1, # Interested in reads by specific user
).exists().label('is_read')
)
comment_query = session.query(Comment, comment_read_query).subquery()
news = session.query(News).outerjoin(comment_query).all()
# How can I get `is_read` column value as comment attribute?
assert news[0].comments[0].is_read
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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