Hi, I'm attempting to load some filtered relationships, and am running into issues when trying to independently load the same relationship multiple times.
As an example, I'd like to load Album.tracks, and Album.tracks.album.tracks in different ways. In the first tracks relationship, I'm trying to include all tracks with track_id >= 4, and in the second relationship every trackId < 4. Is this possible? And if so, what load options or technique should I be using? The query generated below contains all the information I'm trying to get, it's a matter of loading that information into my models that's tripping me up. Complete/runnable example can be found attached or below: from sqlalchemy import create_engine from sqlalchemy.orm import aliased, sessionmaker, relationship, contains_eager from sqlalchemy import Column, ForeignKey, Integer, Unicode from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() metadata = Base.metadata class Album(Base): __tablename__ = 'Album' album_id = Column("AlbumId", Integer, primary_key=True) title = Column("Title", Unicode(160), nullable=False) class Track(Base): __tablename__ = 'Track' track_id = Column("TrackId", Integer, primary_key=True) name = Column("Name", Unicode(200), nullable=False) album_id = Column("AlbumId", ForeignKey('Album.AlbumId'), index=True) album = relationship('Album', backref="tracks") engine = create_engine('sqlite://', echo=True) Base.metadata.create_all(engine, checkfirst=True) session_cls = sessionmaker(bind=engine) session = session_cls() # Set up the database with Chinook data session.add(Album(album_id=1, title="For Those About To Rock We Salute You")) session.add(Album(album_id=2, title="Balls to the Wall")) session.add(Album(album_id=3, title="Restless and Wild")) session.add(Album(album_id=4, title="Let There Be Rock")) session.add(Track(track_id=1, name="For Those About To Rock", album_id=1)) session.add(Track(track_id=2, name="Balls to the Wall", album_id=2)) session.add(Track(track_id=3, name="Fast As a Shark", album_id=3)) session.add(Track(track_id=4, name="Restless and Wild", album_id=3)) session.add(Track(track_id=5, name="Princess of the Dawn", album_id=3)) session.add(Track(track_id=6, name="Put The Finger On You", album_id=1)) session.add(Track(track_id=7, name="Let's Get It Up", album_id=1)) session.add(Track(track_id=8, name="Inject The Venom", album_id=1)) session.add(Track(track_id=9, name="Snowballed", album_id=1)) session.add(Track(track_id=10, name="Evil Walks", album_id=1)) session.add(Track(track_id=11, name="C.O.D.", album_id=1)) session.add(Track(track_id=12, name="Breaking The Rules", album_id=1)) session.add(Track(track_id=13, name="Night Of The Long Knives", album_id=1)) session.add(Track(track_id=14, name="Spellbound", album_id=1)) session.add(Track(track_id=15, name="Go Down" , album_id=4)) session.add(Track(track_id=16, name="Dog Eat Dog", album_id=4)) session.add(Track(track_id=17, name="Let There Be Rock", album_id=4)) session.add(Track(track_id=18, name="Bad Boy Boogie", album_id=4)) session.add(Track(track_id=19, name="Problem Child", album_id=4)) session.add(Track(track_id=20, name="Overdose", album_id=4)) session.add(Track(track_id=21, name="Hell Aint A Bad Place To Be", album_id=4)) session.add(Track(track_id=22, name="Whole Lotta Rosie", album_id=4)) session.commit() # Query set up query = session.query(Album).filter(Album.album_id == 1) track_1_alias = aliased(Track, name="Track1") album_2_alias = aliased(Album, name="Album2") track_2_alias = aliased(Track, name="Track2") # Subqueries we want to load our relationships from # This will match 9 tracks for AlbumId==1 track_1_subquery = session.query(track_1_alias).filter( track_1_alias.track_id >= 4).subquery("Track1") album_2_subquery = session.query(album_2_alias).subquery("Album2") # This should only match 1 track for AlbumId==1 track_2_subquery = session.query(track_2_alias).filter( track_2_alias.track_id < 4).subquery("Track2") # Set up our joins query = query.outerjoin(track_1_subquery, Album.tracks) query = query.outerjoin(album_2_subquery, track_1_alias.album) # Using album_2_alias.tracks for the second argument doesn't seem to work here. query = query.outerjoin(track_2_subquery, album_2_alias.album_id == track_2_alias.album_id) # Options - These don't work all at once, but seem fine separately option1 = contains_eager("tracks", alias=track_1_subquery) option2 = contains_eager("tracks.album", alias=album_2_subquery) option3 = contains_eager("tracks.album.tracks", alias=track_2_subquery) # Attempt to load just tracks option3_query = query.options(option3) results = option3_query.all() assert(len(results) == 1) # len here should be 9, but it's erroneously filtered to 1 assert(len(results[0].tracks) == 1) assert(len(results[0].tracks[0].album.tracks) == 1) -- 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 Example. 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from sqlalchemy import create_engine from sqlalchemy.orm import aliased, sessionmaker, relationship, contains_eager from sqlalchemy import Column, ForeignKey, Integer, Unicode from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() metadata = Base.metadata class Album(Base): __tablename__ = 'Album' album_id = Column("AlbumId", Integer, primary_key=True) title = Column("Title", Unicode(160), nullable=False) class Track(Base): __tablename__ = 'Track' track_id = Column("TrackId", Integer, primary_key=True) name = Column("Name", Unicode(200), nullable=False) album_id = Column("AlbumId", ForeignKey('Album.AlbumId'), index=True) album = relationship('Album', backref="tracks") engine = create_engine('sqlite://', echo=True) Base.metadata.create_all(engine, checkfirst=True) session_cls = sessionmaker(bind=engine) session = session_cls() # Set up the database with Chinook data session.add(Album(album_id=1, title="For Those About To Rock We Salute You")) session.add(Album(album_id=2, title="Balls to the Wall")) session.add(Album(album_id=3, title="Restless and Wild")) session.add(Album(album_id=4, title="Let There Be Rock")) session.add(Track(track_id=1, name="For Those About To Rock", album_id=1)) session.add(Track(track_id=2, name="Balls to the Wall", album_id=2)) session.add(Track(track_id=3, name="Fast As a Shark", album_id=3)) session.add(Track(track_id=4, name="Restless and Wild", album_id=3)) session.add(Track(track_id=5, name="Princess of the Dawn", album_id=3)) session.add(Track(track_id=6, name="Put The Finger On You", album_id=1)) session.add(Track(track_id=7, name="Let's Get It Up", album_id=1)) session.add(Track(track_id=8, name="Inject The Venom", album_id=1)) session.add(Track(track_id=9, name="Snowballed", album_id=1)) session.add(Track(track_id=10, name="Evil Walks", album_id=1)) session.add(Track(track_id=11, name="C.O.D.", album_id=1)) session.add(Track(track_id=12, name="Breaking The Rules", album_id=1)) session.add(Track(track_id=13, name="Night Of The Long Knives", album_id=1)) session.add(Track(track_id=14, name="Spellbound", album_id=1)) session.add(Track(track_id=15, name="Go Down" , album_id=4)) session.add(Track(track_id=16, name="Dog Eat Dog", album_id=4)) session.add(Track(track_id=17, name="Let There Be Rock", album_id=4)) session.add(Track(track_id=18, name="Bad Boy Boogie", album_id=4)) session.add(Track(track_id=19, name="Problem Child", album_id=4)) session.add(Track(track_id=20, name="Overdose", album_id=4)) session.add(Track(track_id=21, name="Hell Aint A Bad Place To Be", album_id=4)) session.add(Track(track_id=22, name="Whole Lotta Rosie", album_id=4)) session.commit() # Query set up query = session.query(Album).filter(Album.album_id == 1) track_1_alias = aliased(Track, name="Track1") album_2_alias = aliased(Album, name="Album2") track_2_alias = aliased(Track, name="Track2") # Subqueries we want to load our relationships from # This will match 9 tracks for AlbumId==1 track_1_subquery = session.query(track_1_alias).filter( track_1_alias.track_id >= 4).subquery("Track1") album_2_subquery = session.query(album_2_alias).subquery("Album2") # This should only match 1 track for AlbumId==1 track_2_subquery = session.query(track_2_alias).filter( track_2_alias.track_id < 4).subquery("Track2") # Set up our joins query = query.outerjoin(track_1_subquery, Album.tracks) query = query.outerjoin(album_2_subquery, track_1_alias.album) # Using album_2_alias.tracks for the second argument doesn't seem to work here. query = query.outerjoin(track_2_subquery, album_2_alias.album_id == track_2_alias.album_id) # Options - These don't work all at once, but seem fine separately option1 = contains_eager("tracks", alias=track_1_subquery) option2 = contains_eager("tracks.album", alias=album_2_subquery) option3 = contains_eager("tracks.album.tracks", alias=track_2_subquery) # Attempt to load just tracks option3_query = query.options(option3) results = option3_query.all() assert(len(results) == 1) # len here should be 9, but it's erroneously filtered to 1 assert(len(results[0].tracks) == 1) assert(len(results[0].tracks[0].album.tracks) == 1)