Assuming you have a (simplified) model like below:
user_to_interest = Table('user_to_interest', Base.metadata,
Column('id', Integer, primary_key=True),
Column('user_id', Integer, ForeignKey('user.id')),
Column('interest_id', Integer, ForeignKey('interest.id'))
)
event_to_interest = Table('event_to_interest', Base.metadata,
Column('id', Integer, primary_key=True),
Column('event_id', Integer, ForeignKey('event.id')),
Column('interest_id', Integer, ForeignKey('interest.id'))
)
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String)
class Event(Base):
__tablename__ = 'event'
id = Column(Integer, primary_key=True)
name = Column(String)
class Interest(Base):
__tablename__ = 'interest'
id = Column(Integer, primary_key=True)
name = Column(String)
users = relationship(User, secondary=user_to_interest, backref="interests")
events = relationship(Event, secondary=event_to_interest, backref="interests")
Version-1: you should be able to do simple query on list of interest_id
s, which will generate basically the SQL
statement you desire:
interest_ids = [10, 144, 432]
query = session.query(Event.name)
query = query.join(event_to_interest, event_to_interest.c.event_id == Event.id)
query = query.filter(event_to_interest.c.interest_id.in_(interest_ids))
However, if there are events which have two or more of the interests from the list, the query will return the same Event.name
multiple times. You can work-around it by using distinct
though: query = session.query(Event.name.distinct())
Version-2: Alternatively, you could do this using just relationships, which will generate different SQL
using sub-query with EXISTS
clause, but semantically it should be the same:
query = session.query(Event.name)
query = query.filter(Event.interests.any(Interest.id.in_(interest_ids)))
This version does not have a problem with duplicates.
However, I would go one step back, and assume that you do get interest_ids
for particular user, and would create a query that works for a user_id
(or User.id
)
Final Version: using any
twice:
def get_events_for_user(user_id):
#query = session.query(Event.name)
query = session.query(Event) # @note: I assume name is not enough
query = query.filter(Event.interests.any(Interest.users.any(User.id == user_id)))
return query.all()
One can agrue that this creates not so beautiful SQL statement, but this is exactly the beauty of using SQLAlchemy which hides the implementation details.
Bonus: you might actually want to give higher priority to the events which have more overlapping interests. In this case the below could help:
query = session.query(Event, func.count('*').label("num_interests"))
query = query.join(Interest, Event.interests)
query = query.join(User, Interest.users)
query = query.filter(User.id == user_id)
query = query.group_by(Event)
# first order by overlaping interests, then also by event.date
query = query.order_by(func.count('*').label("num_interests").desc())
#query = query.order_by(Event.date)