I have a many-to-many relationship between say blog entries and tags. Now I want to know how many entries a specific tag has.
Imagine the following models (simplified):
rel_entries_tags = Table('rel_entries_tags', Base.metadata,
Column('entry_id', Integer, ForeignKey('entries.id')),
Column('tag_id', Integer, ForeignKey('tags.id'))
)
class Entry(Base):
__tablename__ = 'entries'
id = Column(Integer, primary_key=True)
title = Column(String(80))
text = Column(Text)
tags = relationship('Tag', secondary=rel_entries_tags, backref=backref('entries'))
def __init__(self, title, text):
self.title = title
self.text = text
self.tags = tags
class Tag(Base):
__tablename__ = 'tags'
id = Column(Integer, primary_key=True)
name = Column(String(80), unique=True, nullable=False)
def __init__(self, name):
self.name = name
My approach to count the amount of entries for a tag is len(db_session.query(Tag).get(1).entries). The problem is that when it gets db_session.query(Tag).get(1).entries SQLAlchemy selects all the entries with all their columns for a tag, however, I want only the amount of the entries, not the entries themselves. Is there a more optimal approach for this problem?
Thanks.
session.query(Entry).join(Entry.tags).filter(Tag.id==1).count()
or if you have a Tag already
session.query(Entry).with_parent(mytag, "entries").count()
Related
I have this database schema:
class Profile_Eval(Base):
__tablename__ = 'profile_eval'
id = Column(Integer, primary_key=True)
url = Column(String(), unique=True)
job_descriptions = relationship("Job_Description", back_populates='profile')
def __init__(self, url=None):
self.url = url
class Job_Description(Base):
__tablename__ = 'job_description'
id = Column(Integer, primary_key=True)
data = Column(String())
profile_eval_id = Column(Integer, ForeignKey('profile_eval.id'))
profile = relationship("Profile_Eval", back_populates='job_descriptions')
job_predictions= relationship("Job_Prediction", back_populates='job_description')
def __init__(self, data=None, profile_eval_id=None):
self.data = data
class Job_Prediction(Base):
__tablename__ = 'job_prediction'
id = Column(Integer, primary_key=True)
label = Column(String())
score = Column(String())
job_description_id = Column(Integer, ForeignKey('job_description.id'))
job_description = relationship("Job_Description", back_populates="job_predictions")
def __init__(self, label=None, score=None, job_description_id=None):
self.label = label
self.score = score
The structure is that each profile has many jobs. Each job has many predictions.
I am able to add a profile like:
profile = Profile_Eval(url=url)
and then I am able to add the job descriptions to the profile like:
profile_record.job_descriptions.append(Job_Description(description))
but now I'm a little confused as to how I can add the predictions to each description.
Should I break it out into their own tables and get rid of the relationship? Or is there a way to add them?
Thanks!
Should I break it out into their own tables and get rid of the relationship?
The Job_Prediction is already its own table.
Or is there a way to add them?
yes, add predictions to the descriptions at the same time you're adding the descriptions to the jobs:
job_description = Job_Description(description)
job_description.job_predictions.append(...)
# ^^^ whetever you need, here
profile_record.job_descriptions.append(job_description)
I have a SQLAlchemy model named NoteType with a relationship named sections. The NoteSection table is joined to the NoteType table through NoteTypeToSectionMap.
I want the sections list on the NoteType model to be ordered by the position field on the NoteTypeToSectionMap model. The code I have below seems to randomly be ordering the sections.
Does anyone know how to get the ordering to work?
Thanks!
class NoteType(ModelAbstract):
__tablename__ = "noteType"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(255))
description = db.Column(db.String(255))
sections = db.relationship("NoteSection",
secondary=NoteTypeToSectionMap.__table__,
primaryjoin=id==NoteTypeToSectionMap.__table__.c.noteTypeId,
secondaryjoin=id==NoteTypeToSectionMap.__table__.c.noteSectionId,
order_by=NoteTypeToSectionMap.__table__.c.position)
-
class NoteTypeToSectionMap(ModelAbstract):
__tablename__ = "noteTypeToSectionMap"
id = db.Column(db.Integer, primary_key=True)
noteTypeId = db.Column(db.Integer, db.ForeignKey("noteType.id"))
noteSectionId = db.Column(db.Integer, db.ForeignKey("noteSection.id"))
position = db.Column(db.Integer)
Re-write the relationship as follows.
sections = db.relationship("NoteSection",
secondary=NoteTypeToSectionMap.__table__,
order_by=NoteTypeToSectionMap.__table__.c.position)
I am using SQLAlchemy here, trying to make a couple tables and link them and am having problems implementing this.
class Team(Base):
__tablename__ = "teams"
id = Column(Integer, primary_key=True)
espn_team_id = Column(Integer, unique=True, nullable=False)
games = relationship("Game", order_by="Game.date")
def __init__(self, name):
self.name = name
self.espn_team_id = espn_team_id
self.games = games
class Game(Base):
__tablename__ = "games"
id = Column(Integer, primary_key=True)
espn_game_id=Column(Integer, unique=True, nullable=False)
date = Column(Date)
h_espn_id = Column(Integer, ForeignKey('teams.espn_team_id'))
a_espn_id = Column(Integer, ForeignKey('teams.espn_team_id'))
I have this in one file which I use to create the tables. Then in another file I use the insert() function to put values into both tables. I think if I have a team with espn_team_id 360, and then I put in multiple games into the game table which have either h_espn_id=360, or a_espn_id=360, i should be able to do:
a = Table("teams", metadata, autoload=True)
a = session.query(a).filter(a.c.espn_team_id==360).first().games
and it should give me a list of all games team with ID 360 has played. But instead I get this error
AttributeError: 'NamedTuple' object has no attribute 'games'
What am I misunderstanding about SQLAlchemy or relational databases here?
Firstly, you don't have to create another Table object, as it is available as Team.__table__. Anyway, you can just query the mapped class, e.g.
query = Session.query(Team).filter(Team.espn_team_id == 360)
team360 = query.one()
games = team360.games
Refer to the documentation for methods .one(), .first(), and .all(): http://docs.sqlalchemy.org/en/latest/orm/query.html
Here is the solution I found, took way too long to understand this...
class Team(Base):
__tablename__ = "teams"
id = Column(Integer, primary_key=True)
name = Column(String)
espn_team_id = Column(Integer, unique=True, nullable=False)
h_games = relationship(
"Game",
primaryjoin="Game.h_espn_id==Team.espn_team_id",
order_by="Game.date")
a_games = relationship(
"Game",
primaryjoin="Game.a_espn_id==Team.espn_team_id",
order_by="Game.date")
#hybrid_property
def games(self):
return self.h_games+self.a_games
def __init__(self, name):
self.name = name
self.espn_team_id = espn_team_id
self.h_games = h_games
self.a_games = a_games
self.games = games
I have two models, related with many-to-many, one of them is hierarchical model:
#hierarchical model
class Tag(Base):
__tablename__ = "tags"
id = Column(Integer, primary_key=True)
name = Column(String)
Tag.parent_id = Column(Integer, ForeignKey(Tag.id, ondelete='CASCADE'))
Tag.childs = relationship(Tag, backref=backref('parent', remote_side=[Tag.id]),
cascade="all, delete")
class Subject(Base):
__tablename__ = "subjects"
id = Column(Integer, primary_key=True, doc="ID")
name = Column(String)
tags = relationship(Tag, secondary="tags_subjects", backref="subjects")
#many-to-many relations model
class TagsSubjects(Base):
__tablename__ = "tags_subjects"
id = Column(Integer, primary_key=True)
tag_id = Column(Integer, ForeignKey("tags.id"))
subject_id = Column(Integer, ForeignKey("subjects.id"))
So, I'll try to explain what I want to do... I want to make one (or several) query, for search all Subject's objects,
that have 'name' field value like 'foo' OR that has related tags having names with values like 'foo'
OR that has related tags, that has one or more parents (or above by hierarchy) tag with 'name' value like 'foo'
I've tried to do somethis like this:
>>> subjects = session.query(Subject).filter(or_(
Subject.name.ilike('%{0}%'.format('foo')),
Subject.tags.any(
Tag.name.ilike('%{0}%'.format('foo')))
)).order_by(Subject.name).all()
But it isn't correct and "flat" query, without hierarchical feature :(
How to do this by SQLAlchemy's API?
Thanks!
P.S. I'm using SQLite backend
I created a many to many relationship with sqlalchemy like this:
subject_books = Table('subject_books', Base.metadata,
Column('subject_id', Integer, ForeignKey('subjects.id')),
Column('book_id', Integer, ForeignKey('books.id')),
Column('group', Integer)
)
class Subject(Base):
__tablename__ = 'subjects'
id = Column(Integer, primary_key=True)
value = Column(Unicode(255), unique=True)
class Book(Base):
__tablename__ = 'books'
id = Column(Integer, primary_key=True)
title = Column(Unicode(255))
isbn = Column(Unicode(24))
subjects = relationship('Subject', secondary=subject_books, collection_class=attribute_mapped_collection('group'), backref='books')
after that I created a test like following:
book = Book(title='first book',isbn='test')
book.subjects[0] = Subject(value='first subject')
book.subjects[1] = Subject(value='second subject')
session.add(book)
transaction.commit()
and it works fine. But what I really want is to store more than one subject with the same group value, so I tried the following test:
book = Book(title='first book',isbn='test')
book.subjects[0] = [Subject(value='first subject'),Subject(value='second subject')]
book.subjects[1] = [Subject(value='third subject'),Subject(value='forth subject')]
session.add(book)
transaction.commit()
but it does not work.
Can this be done using sqlalchemy?
Thanks in Advance
Razi
I think you are constructing wrong relation ship.
Your relation ship must be
book M2M subject
subject M2M group
So you have to create one more model for group and that must be assign as m2m in Subject
Your models will be like.
subject_books = Table('subject_books', Base.metadata,
Column('subject_id', Integer, ForeignKey('subjects.id')),
Column('book_id', Integer, ForeignKey('books.id')),
)
subject_group = Table('subject_groups', Base.metadata,
Column('group_id', Integer, ForeignKey('groups.id')),
Column('subject_id', Integer, ForeignKey('subjects.id')),
)
class Subject(Base):
__tablename__ = 'subjects'
id = Column(Integer, primary_key=True)
value = Column(Unicode(255), unique=True)
groups = relationship('Groups', secondary=subject_groups, backref='subjects')
class Groups(Base):
__tablename__ = 'groups'
id = Column(Integer, primary_key=True)
name = Column(Unicode(255), unique=True)
class Book(Base):
__tablename__ = 'books'
id = Column(Integer, primary_key=True)
title = Column(Unicode(255))
isbn = Column(Unicode(24))
subjects = relationship('Subject', secondary=subject_books, backref='books')
I also check the docs for attribute_mapped_collection. But each time I found that each key is associated with only one object not more then one. If you read anywhere then please provide the link so I can check that how it will be fit in your code.
I think this will be help you.