It seems like a bit of a workaround to commit changes, query the database for the key, and insert it somewhere else.
I assumed one should use the synonym() function for this, but it doesn't seem to have any effect, i.e. my synonymous column doesn't exist when querying the database afterwards.
E.g.
class MyClass(Base):
__tablename__ = 'my_table'
id = Column(Integer, primary_key=True, autoincrement=True)
job_status = Column(String(50))
other_id = synonym("id")
Related
I know this question has already been asked by I could not find a clean solution.
My problem is simple: I have a table with a many to many association. Where users have many workspaces and workspaces have many users.
invitations_table = db.Table('invitations', db.Model.metadata,
db.Column('user_id', db.Integer, db.ForeignKey('user.id', ondelete='cascade'), primary_key=True),
db.Column('workspace_id', db.Integer, db.ForeignKey('workspace.id', ondelete='cascade'), primary_key=True)
)
Now my two class are declared like that:
class Workspace(db.Model):
id = db.Column(db.Integer, primary_key = True)
...
u_invited = db.relationship("User",
secondary = invitations_table,
cascade = 'all',
back_populates = "w_invited")
class User(db.Model):
id = db.Column(db.Integer, primary_key = True)
...
w_invited = db.relationship("Workspace",
secondary = invitations_table,
back_populates = "u_invited")
Now, If I delete my workspace, I can't cascade the deletion on the associative table as well:
def delete_all_workspace(self):
workspace = Workspace.query.filter_by(owner=self)
# for w in workspace.all():
# w.u_invited.clear()
succeed = workspace.delete()
db.session.commit()
The problem is: I need, as some people suggest, to manually loop into my list of objects then call clear() in order to not get this exception:
sqlalchemy.exc.IntegrityError: (psycopg2.IntegrityError) update or delete on table "workspace" violates foreign key constraint "invitations_workspace_id_fkey" on table "invitations"
DETAIL: Key (id)=(142) is still referenced from table "invitations".
I though ondelete='cascade' will be enough to tell sqlalchemy to delete the associative table as well but that's not working as expected.
My question is: Is there a way to tell SQLAlchemy to clear the associative table invitations as well without having the burden to clear it manually?
Thanks for your answers
I'm trying to retrieve data from multiple tables with SQLAlchemy using the .join() method.
When I run the query I was expecting to get a single object back which had all the data from the different tables joined so that I could use a.area_name and so on where area_name is on one of the joined tables. Below is the query I am running and the table layout, if anyone could offer insight into how to achieve the behavior I'm aiming for I would greatly appreciate it! I've been able to use the .join() method with this same syntax to match results and return them, I figured it would return the extra data from the rows as well since it joins the tables (perhaps I'm misunderstanding how the method works or how to retrieve the information via the query object?).
If it helps with the troubleshooting I'm using MySQL as the database
query:
a = User.query.filter(User.user_id==1).join(UserGroup,
User.usergroup==UserGroup.group_id).join(Areas, User.area==Areas.area_id).first()
and the tables:
class User(db.Model):
user_id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(20), unique=True)
usergroup = db.Column(db.Integer, db.ForeignKey('user_group.group_id'), nullable=False)
area = db.Column(db.Integer, db.ForeignKey('areas.area_id'), nullable=False)
class UserGroups(db.Model):
id = db.Column(db.Integer, primary_key=True)
group_id = db.Column(db.Integer, nullable=False, unique=True)
group_name = db.Column(db.String(64), nullable=False, unique=True)
class Areas(db.Model):
id = db.Column(db.Integer, primary_key=True)
area_id = db.Column(db.Integer, nullable=False, unique=True)
area_name = db.Column(db.String(64), nullable=False, unique=True)
So it seems that I need to use a different approach to the query, and that it returns a tuple of objects which I then need to parse.
What worked is:
a = db.session.query(User, UserGroups, Areas
).filter(User.user_id==1
).join(UserGroup,User.usergroup==UserGroup.group_id
).join(Areas, User.area==Areas.area_id
).first()
The rest remaining the same. This then returned a tuple that I could parse where the data from User is a[0], from UserGroups is a[1], and Areas is a[2]. I can then access the group_name column with a[1].group_name etc.
Hopefully this helps someone else who's trying to work with this!
Take a look at SQLAlchemy's relationship function:
http://docs.sqlalchemy.org/en/latest/orm/basic_relationships.html#one-to-many
You may want to add a new attribute to your User class like so:
group = sqlalchemy.relationship('UserGroups', back_populates='users')
This will automagically resolve the one-to-many relationship between User and UserGroups (assuming that a User can only be member of one UserGroup at a time). You can then simply access the attributes of the UserGroup once you have queried a User (or set of Users) from your database:
a = User.query.filter(...).first()
print(a.group.group_name)
SQLAlchemy resolves the joins for you, you do not need to explicitly join the foreign tables when querying.
The reverse access is also possible; if you just query for a UserGroup, you can access the corresponding members directly (via the back_populates-keyword argument):
g = UserGroup.query.filter(...).first()
for u in g.users:
print(u.name)
Do you set your foreign keys as nullable=false if always expect a foreign key on that column in the database?
I'm using sqlalchemy and have set my models with required foreign keys. This sometimes causes me to run session.commit() more often, since I need the parent model to have an id and be fully created in order to build a child object in the ORM. What is considered best practice? My models are below:
class Location(Base):
__tablename__ = 'locations'
id = Column(Integer, primary_key=True)
city = Column(String(50), nullable=False, unique=True)
hotels = relationship('Hotel', back_populates='location')
class Hotel(Base):
__tablename__ = 'hotels'
id = Column(Integer, primary_key=True)
name = Column(String(100), nullable=False, unique=True)
phone_number = Column(String(20))
parking_fee = Column(String(10))
location_id = Column(Integer, ForeignKey('locations.id'), nullable=False)
location = relationship('Location', back_populates='hotels')
You don't need to do session.commit() to get an ID; session.flush() will do.
Even better, you don't need to get an ID at all if you set the relationship because SQLalchemy will figure out the order to do the INSERTs in. You can simply do:
loc = Location(city="NYC", hotels=[Hotel(name="Hilton")])
session.add(loc)
session.commit()
and it will work fine.
I would suggest that you'd better not set nullable=False. Make foreign key nullable is very reasonable in many situations. In your scenario, for example, if I want to insert a hotel whose location is currently underdetermined, you can not accomplish this with the foreign key not null. So the best practice when using foreign key is to set it nullable.
See necessary nullable foreign key Any example of a necessary nullable foreign key?
I have a MySQL table, defined in sqlalchemy with following structure:
class User(Base):
__tablename__ = 'user'
__table_args__ = {'mysql_charset': 'utf8', 'mysql_engine': 'InnoDB'}
id = Column(Integer, primary_key=True)
handle = Column(String(250), nullable=False)
owned = Column(Boolean(), default=False)
owner_id = Column(Integer, ForeignKey("user.id"), nullable=True, default=null )
current_price = Column(Integer, nullable=False, default=1)
balance = Column(Integer, nullable=False, default=0)
I want a relationship so that the owner_id can either be null, OR if it is set it must refer to a valid user.id, in the same table.
I don't quite understand the sqlalchemy relationship stuff well enough to be able to do it. The special stuff at the top of this page http://docs.sqlalchemy.org/en/latest/orm/relationship_persistence.html seems to suggest that it's possible, but I can't figure it out.
I want to then be able to either add Users like:
u1 = User(handle="bob")
u2 = User(handle="jim", owner=u1)
Thanks for any help!
I should add that sqlalchemy has no problem doing the CREATE TABLE with the correct FOREIGN KEY constraint, and I can manually INSERT data into the table that obeys the rules as I want them in MySQL, it's only using the sqlalchemy model that fails.
EDIT: SOLVED
The 'default=null' on owner_id was causing the problem for some reason. Helpful docs were here: http://docs.sqlalchemy.org/en/rel_1_0/orm/self_referential.html and code example from that page here: http://docs.sqlalchemy.org/en/rel_1_0/orm/examples.html#examples-adjacencylist
For the google spider bots, errors that I got during this process were:
sqlalchemy.exc.IntegrityError: (_mysql_exceptions.IntegrityError) (1452, 'Cannot add or update a child row: a foreign key constraint fails (`twitfriends`.`tree`, CONSTRAINT `tree_ibfk_1` FOREIGN KEY (`parent_id`) REFERENCES `tree` (`id`))') [SQL: u'INSERT INTO tree (parent_id, name) VALUES (%s, %s)'] [parameters: (<sqlalchemy.sql.elements.Null object at 0x7fe7e8c468d0>, 'rootnode')]
And
ArgumentError: Node.next and back-reference Node.prev are both of the same direction <symbol 'ONETOMANY>. Did you mean to set remote_side on the many-to-one side ?
Since there is only one foreign key for User, I would expect sqlalchemy to automatically figure out the join conditions. You can also add a backref so you can get the other side of the relationship.
class User(Base):
...
owner = relationship('User', remote_side=['id'], backref='owned_users')
Docs
Ex.
u1 = User(handle="bob")
u2 = User(handle="jim", owner=u1)
print u2.owned_users[0] == u1
# True
I have this code, thats been mostly taken from the sqlalchemy site
class Order(Base):
__tablename__ = 'order'
id = Column(Integer, Sequence('tri_id_seq'), primary_key=True)
text = Column(String(1024), nullable=False)
items = relationship("Item", cascade="save-update, delete-orphan, merge, delete", backref="parent")
class Item(Base):
__tablename__ = 'item'
id = Column(Integer, Sequence('tri_id_seq'), primary_key=True)
text = Column(String(1024), nullable=False)
parent_id = Column(Integer, ForeignKey('order.id'))
I want deletes to Order to cascade down and delete its items as well. In code:
# test insert/delete - save data to mssql server
i1 = Item(text="item one")
i2 = Item(text="item two")
o = Order(text="one", items=[i1, i2])
session.add(o)
session.commit()
session.delete(o) # delete it
# tests to make sure items/order gone ....
session.commit()
This works ok.
BUT if I try and delete an Order in MS SQL management studio. i.e.
DELETE FROM [dbo].[order] WHERE id = 1
I get the error
"the DELETE statement conflicted with the REFERENCE constraint FK__item__parent_id_1D00044F" The conflict error blah blah....
I guess theres something missing on the relationship definitions but I can't see it.
Any help/thoughts?
ta.
class Comment(Base):
__tablename__ = 'comments'
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey("users.id", ondelete='CASCADE'), nullable=False)
user = relationship("User", backref=backref('comments', cascade="all,delete", order_by=id))
This kind of setup works for me, my User class doesn't have any special fields except for primary key.
So basically, this works as intended, when I delete the user - his comments are gone as well.
It doesn't have to be deletion through SQLAlchemy either, this code creates an appropriate table structure, that even if you delete user manually (sql query) - cascade deletion will still work.