Re: [sqlalchemy] newest address for each user
Thank you for the help! Additionally, I was wondering if it would be
able to make newest_address an attribute on the user class, which can
then be used in a query with .options(joinedload('newest_address')).
My goal would be that I get an attribute that returns the newest'
address date time on normal access and is also able to be eagerly
loaded/joined in a query object. I read up in the docs and either
column_property or Correlated Subquery Relatonship Hybrid seems to be
made for this. Which one should I use?
ButAm 20.10.2013 04:41, schrieb Michael Bayer:
On Oct 19, 2013, at 4:24 PM, Sebastian Elsner sebast...@risefx.com wrote:
Hello,
using the Address and User example, where the Address is connected to
the User via a many-to-many relationship, I want to get all users with
the date of their newest address. This is what I have now:
s.query(User, s.query(func.max(Address.created)).\
filter(Address.users.any()).correlate(User).as_scalar()).\
outerjoin(User.addresses).all()
But this is giving me all users with the newest address in the whole
address table. I think the error is in the subquery's filter, but I fail
to see how I can fix it. I am also not tied to this query, so if you
know a better way to get a list of all Users and their newest address
date, shoot!
the format for this is the select user rows + an aggregate of a related
table, this format is illustrated here:
http://docs.sqlalchemy.org/en/rel_0_8/orm/tutorial.html#using-subqueries
where we illustrate the count of address rows per user.
I see here though you have an association table in between them so that just
has to be added to the subquery to create a row that goes across Address and
UserAddresses, same idea though, use subquery with aggregate + group_by,
(outer) join to that:
subq = session.query(
func.max(Address.created).label(created),
UserAddresses.user_id).join(UserAddresses).\
group_by(UserAddresses.user_id).subquery()
q = session.query(User, subq.c.created).outerjoin(subq)
print q.all()
Here is a working example. As you can see if you run it, even Users with
no Addresses assigned will get the newest address date in the query.
import datetime
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.engine import create_engine
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer, DateTime, String
from sqlalchemy.orm import relationship
from sqlalchemy.sql.expression import func
Base = declarative_base()
class Address(Base):
__tablename__ = 'address'
id = Column(Integer, primary_key=True)
created = Column(DateTime)
users = relationship('User', back_populates='addresses',
secondary='useraddress')
def __repr__(self):
return Address: %s, %s % (self.id, self.created)
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String)
addresses = relationship('Address', back_populates='users',
secondary='useraddress')
def __repr__(self):
return User: + self.name
class UserAddresses(Base):
__tablename__ = 'useraddress'
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
address_id = Column(Integer, ForeignKey('address.id'), primary_key=True)
engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
u1 = User(name=Foo)
u2 = User(name=Bar)
u1.addresses.append(Address(created=datetime.datetime.now()))
u1.addresses.append(Address(created=datetime.datetime.now() -
datetime.timedelta(days=1)))
session.add(u1)
session.add(u2)
session.commit()
print u1, u1.addresses
print u2, u2.addresses
print session.query(User, print session.query(User,
session.query(func.max(Address.created)).filter(Address.users.any()).correlate(User).as_scalar()).outerjoin(User.addresses).all()
Cheers
Sebastian
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Re: [sqlalchemy] Occasional InvalidRequestError: Table 'xxx' is already defined for this MetaData instance.
Hi Michael,
I spoke with the developer of the application that launches the plugins I
am writing and each
python script is run by starting an entirely new process with
the interpreter and each plugin.
It should be a clean environment. From the plugins, I simply import which
ever tables from
the module below that I would need.
In the event I am doing something wrong, my code looks like:
from os import path
from sqlalchemy import (
Column, CheckConstraint, DDL, ForeignKey, Index, Integer, String,
create_engine, event
)
from sqlalchemy.engine import Engine
from sqlalchemy.ext.declarative import declared_attr, declarative_base
from sqlalchemy.orm import sessionmaker
db_name = path.join('path', 'config', 'sqlite.db')
engine = create_engine('sqlite:///{}'.format(db_name), echo=False)
Session = sessionmaker(bind=engine, autoflush=False, autocommit=False)
Base = declarative_base()
@event.listens_for(Engine, 'connect')
def set_sqlite_pragma(dbapi_connection, connection_record):
cursor = dbapi_connection.cursor()
cursor.execute('PRAGMA foreign_keys=ON')
cursor.close()
table defs...
if __name__ == '__main__':
Base.metadata.create_all(engine)
Thanks so much for the help,
jlc
On Sun, Oct 20, 2013 at 11:01 PM, Michael Bayer mike...@zzzcomputing.comwrote:
the MetaData object holds one Table object per unique name given. If you
use the Table constructor more than once with the same name and the same
MetaData, you get this error.
That's how the error is caused, then the fact that the error is
occasional points strongly to a race condition of some kind, more than
one thread both calling the constructor for Table with the same name.
Patterns that could cause this could be some kind of unsynchronized global
registry or singleton object that when called produces a new Table object.
The recommended pattern is for Table objects (as well as mapped classes)
to generally be declared at the module level so that these names are
produced only at module import time, which itself should occur before the
application starts any threads in addition to the main application thread.
On Oct 20, 2013, at 11:04 PM, Joseph Casale jcas...@gmail.com wrote:
I have a module that is imported by several Python scripts run by an
application
that fires up a new interpreter session for each invocation. When not
under load or
running the code manually at the cli things work fine but once the
concurrency
raises and the application starts seeing some load it emits
InvalidRequestError
exceptions on one table.
After searching I am not sure the results relate to my issue or maybe my
lack
of familiarity with SQLAlchemy has the better of me.
Any guidance would be greatly appreciated,
jlc
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[sqlalchemy] quelified/disambiguated column names in query
Hello, Say that i have a table with reports with a column 'title' and a one to many relationship 'chapters' to chapters also with a column 'title', if i join these tables in a query, like: q = self.session.query(Report).join(Report.chapters).add_columns(Report.title, Chapter.title, Chapter.text) for p in q.all(): print p.title print p.title prints the title of the chapter. Is there a way to let the query.all() return NamedTuples with qualified/disambiguated names (either 'title' and 'chapters.title' or 'Report.title' and 'Chapter.title' or perhaps with underscores), because now i see no way to distinguish the columns (apart maybe from the order). p.keys() returns 'title' twice. Cheers, Lars PS: i am using sqla 0.7.5 -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/groups/opt_out.
Re: [sqlalchemy] Occasional InvalidRequestError: Table 'xxx' is already defined for this MetaData instance.
how about a stack trace?
On Oct 21, 2013, at 4:11 PM, Joseph Casale jcas...@gmail.com wrote:
Hi Michael,
I spoke with the developer of the application that launches the plugins I am
writing and each
python script is run by starting an entirely new process with the interpreter
and each plugin.
It should be a clean environment. From the plugins, I simply import which
ever tables from
the module below that I would need.
In the event I am doing something wrong, my code looks like:
from os import path
from sqlalchemy import (
Column, CheckConstraint, DDL, ForeignKey, Index, Integer, String,
create_engine, event
)
from sqlalchemy.engine import Engine
from sqlalchemy.ext.declarative import declared_attr, declarative_base
from sqlalchemy.orm import sessionmaker
db_name = path.join('path', 'config', 'sqlite.db')
engine = create_engine('sqlite:///{}'.format(db_name), echo=False)
Session = sessionmaker(bind=engine, autoflush=False, autocommit=False)
Base = declarative_base()
@event.listens_for(Engine, 'connect')
def set_sqlite_pragma(dbapi_connection, connection_record):
cursor = dbapi_connection.cursor()
cursor.execute('PRAGMA foreign_keys=ON')
cursor.close()
table defs...
if __name__ == '__main__':
Base.metadata.create_all(engine)
Thanks so much for the help,
jlc
On Sun, Oct 20, 2013 at 11:01 PM, Michael Bayer mike...@zzzcomputing.com
wrote:
the MetaData object holds one Table object per unique name given. If you
use the Table constructor more than once with the same name and the same
MetaData, you get this error.
That's how the error is caused, then the fact that the error is occasional
points strongly to a race condition of some kind, more than one thread both
calling the constructor for Table with the same name. Patterns that could
cause this could be some kind of unsynchronized global registry or singleton
object that when called produces a new Table object.
The recommended pattern is for Table objects (as well as mapped classes) to
generally be declared at the module level so that these names are produced
only at module import time, which itself should occur before the application
starts any threads in addition to the main application thread.
On Oct 20, 2013, at 11:04 PM, Joseph Casale jcas...@gmail.com wrote:
I have a module that is imported by several Python scripts run by an
application
that fires up a new interpreter session for each invocation. When not under
load or
running the code manually at the cli things work fine but once the
concurrency
raises and the application starts seeing some load it emits
InvalidRequestError
exceptions on one table.
After searching I am not sure the results relate to my issue or maybe my lack
of familiarity with SQLAlchemy has the better of me.
Any guidance would be greatly appreciated,
jlc
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Re: [sqlalchemy] quelified/disambiguated column names in query
On Oct 21, 2013, at 5:20 PM, lars van gemerden l...@rational-it.com wrote: Hello, Say that i have a table with reports with a column 'title' and a one to many relationship 'chapters' to chapters also with a column 'title', if i join these tables in a query, like: q = self.session.query(Report).join(Report.chapters).add_columns(Report.title, Chapter.title, Chapter.text) for p in q.all(): print p.title print p.title prints the title of the chapter. Is there a way to let the query.all() return NamedTuples with qualified/disambiguated names (either 'title' and 'chapters.title' or 'Report.title' and 'Chapter.title' or perhaps with underscores), because now i see no way to distinguish the columns (apart maybe from the order). p.keys() returns 'title' twice. use labels: add_columns(Report.title.label(report_title), Chapter.title.label(chapter_title)) Cheers, Lars PS: i am using sqla 0.7.5 -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/groups/opt_out. signature.asc Description: Message signed with OpenPGP using GPGMail
Re: [sqlalchemy] newest address for each user
if we're talking about just the timestamp, then that would be a column property
and if you don't want it to load normally it would be under a deferred().
An analogue of the subquery example using count() is here:
http://docs.sqlalchemy.org/en/rel_0_8/orm/mapper_config.html#using-column-property
again, you can adapt this to look like your max() + association table:
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
address_created = column_property(
select([func.max(Address.created)]).\
where(Address.id == UserAddresses.address_id).\
where(UserAddresses.user_id == id).\
correlate_except(Address, UserAddresses)
)
On Oct 21, 2013, at 3:12 AM, Sebastian Elsner sebast...@risefx.com wrote:
Thank you for the help! Additionally, I was wondering if it would be
able to make newest_address an attribute on the user class, which can
then be used in a query with .options(joinedload('newest_address')).
My goal would be that I get an attribute that returns the newest'
address date time on normal access and is also able to be eagerly
loaded/joined in a query object. I read up in the docs and either
column_property or Correlated Subquery Relatonship Hybrid seems to be
made for this. Which one should I use?
ButAm 20.10.2013 04:41, schrieb Michael Bayer:
On Oct 19, 2013, at 4:24 PM, Sebastian Elsner sebast...@risefx.com wrote:
Hello,
using the Address and User example, where the Address is connected to
the User via a many-to-many relationship, I want to get all users with
the date of their newest address. This is what I have now:
s.query(User, s.query(func.max(Address.created)).\
filter(Address.users.any()).correlate(User).as_scalar()).\
outerjoin(User.addresses).all()
But this is giving me all users with the newest address in the whole
address table. I think the error is in the subquery's filter, but I fail
to see how I can fix it. I am also not tied to this query, so if you
know a better way to get a list of all Users and their newest address
date, shoot!
the format for this is the select user rows + an aggregate of a related
table, this format is illustrated here:
http://docs.sqlalchemy.org/en/rel_0_8/orm/tutorial.html#using-subqueries
where we illustrate the count of address rows per user.
I see here though you have an association table in between them so that just
has to be added to the subquery to create a row that goes across Address and
UserAddresses, same idea though, use subquery with aggregate + group_by,
(outer) join to that:
subq = session.query(
func.max(Address.created).label(created),
UserAddresses.user_id).join(UserAddresses).\
group_by(UserAddresses.user_id).subquery()
q = session.query(User, subq.c.created).outerjoin(subq)
print q.all()
Here is a working example. As you can see if you run it, even Users with
no Addresses assigned will get the newest address date in the query.
import datetime
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.engine import create_engine
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer, DateTime, String
from sqlalchemy.orm import relationship
from sqlalchemy.sql.expression import func
Base = declarative_base()
class Address(Base):
__tablename__ = 'address'
id = Column(Integer, primary_key=True)
created = Column(DateTime)
users = relationship('User', back_populates='addresses',
secondary='useraddress')
def __repr__(self):
return Address: %s, %s % (self.id, self.created)
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String)
addresses = relationship('Address', back_populates='users',
secondary='useraddress')
def __repr__(self):
return User: + self.name
class UserAddresses(Base):
__tablename__ = 'useraddress'
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
address_id = Column(Integer, ForeignKey('address.id'), primary_key=True)
engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
u1 = User(name=Foo)
u2 = User(name=Bar)
u1.addresses.append(Address(created=datetime.datetime.now()))
u1.addresses.append(Address(created=datetime.datetime.now() -
datetime.timedelta(days=1)))
session.add(u1)
session.add(u2)
session.commit()
print u1, u1.addresses
print u2, u2.addresses
print session.query(User, print session.query(User,
session.query(func.max(Address.created)).filter(Address.users.any()).correlate(User).as_scalar()).outerjoin(User.addresses).all()
Cheers
Sebastian
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Re: [sqlalchemy] newest address for each user
This is just anazing! I was tinkering with the select statement, but
using the correlate_except would never have come to my mind. Thank you!
Am 22.10.2013 00:16, schrieb Michael Bayer:
if we're talking about just the timestamp, then that would be a column
property and if you don't want it to load normally it would be under a
deferred().
An analogue of the subquery example using count() is here:
http://docs.sqlalchemy.org/en/rel_0_8/orm/mapper_config.html#using-column-property
again, you can adapt this to look like your max() + association table:
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
address_created = column_property(
select([func.max(Address.created)]).\
where(Address.id == UserAddresses.address_id).\
where(UserAddresses.user_id == id).\
correlate_except(Address, UserAddresses)
)
On Oct 21, 2013, at 3:12 AM, Sebastian Elsner sebast...@risefx.com wrote:
Thank you for the help! Additionally, I was wondering if it would be
able to make newest_address an attribute on the user class, which can
then be used in a query with .options(joinedload('newest_address')).
My goal would be that I get an attribute that returns the newest'
address date time on normal access and is also able to be eagerly
loaded/joined in a query object. I read up in the docs and either
column_property or Correlated Subquery Relatonship Hybrid seems to be
made for this. Which one should I use?
ButAm 20.10.2013 04:41, schrieb Michael Bayer:
On Oct 19, 2013, at 4:24 PM, Sebastian Elsner sebast...@risefx.com wrote:
Hello,
using the Address and User example, where the Address is connected to
the User via a many-to-many relationship, I want to get all users with
the date of their newest address. This is what I have now:
s.query(User, s.query(func.max(Address.created)).\
filter(Address.users.any()).correlate(User).as_scalar()).\
outerjoin(User.addresses).all()
But this is giving me all users with the newest address in the whole
address table. I think the error is in the subquery's filter, but I fail
to see how I can fix it. I am also not tied to this query, so if you
know a better way to get a list of all Users and their newest address
date, shoot!
the format for this is the select user rows + an aggregate of a related
table, this format is illustrated here:
http://docs.sqlalchemy.org/en/rel_0_8/orm/tutorial.html#using-subqueries
where we illustrate the count of address rows per user.
I see here though you have an association table in between them so that
just has to be added to the subquery to create a row that goes across
Address and UserAddresses, same idea though, use subquery with aggregate +
group_by, (outer) join to that:
subq = session.query(
func.max(Address.created).label(created),
UserAddresses.user_id).join(UserAddresses).\
group_by(UserAddresses.user_id).subquery()
q = session.query(User, subq.c.created).outerjoin(subq)
print q.all()
Here is a working example. As you can see if you run it, even Users with
no Addresses assigned will get the newest address date in the query.
import datetime
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.engine import create_engine
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer, DateTime, String
from sqlalchemy.orm import relationship
from sqlalchemy.sql.expression import func
Base = declarative_base()
class Address(Base):
__tablename__ = 'address'
id = Column(Integer, primary_key=True)
created = Column(DateTime)
users = relationship('User', back_populates='addresses',
secondary='useraddress')
def __repr__(self):
return Address: %s, %s % (self.id, self.created)
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String)
addresses = relationship('Address', back_populates='users',
secondary='useraddress')
def __repr__(self):
return User: + self.name
class UserAddresses(Base):
__tablename__ = 'useraddress'
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
address_id = Column(Integer, ForeignKey('address.id'), primary_key=True)
engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
u1 = User(name=Foo)
u2 = User(name=Bar)
u1.addresses.append(Address(created=datetime.datetime.now()))
u1.addresses.append(Address(created=datetime.datetime.now() -
datetime.timedelta(days=1)))
session.add(u1)
session.add(u2)
session.commit()
print u1, u1.addresses
print u2, u2.addresses
print session.query(User, print session.query(User,
session.query(func.max(Address.created)).filter(Address.users.any()).correlate(User).as_scalar()).outerjoin(User.addresses).all()
Cheers
Re: [sqlalchemy] Occasional InvalidRequestError: Table 'xxx' is already defined for this MetaData instance.
Hey Michael,
For reasons beyond my control at the moment, logging was utterly butchered
in a completely
incomprehensible means by another developer.
Traceback (most recent call last):
File D:\app_folder\plugin\idm_rw.py, line 6, in module
from idm_config import Attribute, Session
File D:\app_folder\include\idm_config.py, line 478, in module
class PortalConfig(Base, EnvironmentMixin):
File D:\Python33\lib\site-packages\sqlalchemy\ext\declarative\api.py,
line 50, in __init__
_as_declarative(cls, classname, cls.__dict__)
File D:\Python33\lib\site-packages\sqlalchemy\ext\declarative\base.py,
line 222, in
_as_declarative **table_kw)
File D:\Python33\lib\site-packages\sqlalchemy\schema.py, line 319, in
__new__ existing Table object. % key)
sqlalchemy.exc.InvalidRequestTable 'attribute_config' is already
defined for this MetaData instance. Specify 'extend_existing=True' to
redefine
options and columns on an existing Table object.
I think thats what it looked like before he had his way:)
Thanks!
jlc
On Mon, Oct 21, 2013 at 3:25 PM, Michael Bayer mike...@zzzcomputing.comwrote:
how about a stack trace?
On Oct 21, 2013, at 4:11 PM, Joseph Casale jcas...@gmail.com wrote:
Hi Michael,
I spoke with the developer of the application that launches the plugins I
am writing and each
python script is run by starting an entirely new process with
the interpreter and each plugin.
It should be a clean environment. From the plugins, I simply import which
ever tables from
the module below that I would need.
In the event I am doing something wrong, my code looks like:
from os import path
from sqlalchemy import (
Column, CheckConstraint, DDL, ForeignKey, Index, Integer, String,
create_engine, event
)
from sqlalchemy.engine import Engine
from sqlalchemy.ext.declarative import declared_attr, declarative_base
from sqlalchemy.orm import sessionmaker
db_name = path.join('path', 'config', 'sqlite.db')
engine = create_engine('sqlite:///{}'.format(db_name), echo=False)
Session = sessionmaker(bind=engine, autoflush=False, autocommit=False)
Base = declarative_base()
@event.listens_for(Engine, 'connect')
def set_sqlite_pragma(dbapi_connection, connection_record):
cursor = dbapi_connection.cursor()
cursor.execute('PRAGMA foreign_keys=ON')
cursor.close()
table defs...
if __name__ == '__main__':
Base.metadata.create_all(engine)
Thanks so much for the help,
jlc
On Sun, Oct 20, 2013 at 11:01 PM, Michael Bayer
mike...@zzzcomputing.comwrote:
the MetaData object holds one Table object per unique name given. If
you use the Table constructor more than once with the same name and the
same MetaData, you get this error.
That's how the error is caused, then the fact that the error is
occasional points strongly to a race condition of some kind, more than
one thread both calling the constructor for Table with the same name.
Patterns that could cause this could be some kind of unsynchronized global
registry or singleton object that when called produces a new Table object.
The recommended pattern is for Table objects (as well as mapped classes)
to generally be declared at the module level so that these names are
produced only at module import time, which itself should occur before the
application starts any threads in addition to the main application thread.
On Oct 20, 2013, at 11:04 PM, Joseph Casale jcas...@gmail.com wrote:
I have a module that is imported by several Python scripts run by an
application
that fires up a new interpreter session for each invocation. When not
under load or
running the code manually at the cli things work fine but once the
concurrency
raises and the application starts seeing some load it emits
InvalidRequestError
exceptions on one table.
After searching I am not sure the results relate to my issue or maybe my
lack
of familiarity with SQLAlchemy has the better of me.
Any guidance would be greatly appreciated,
jlc
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Re: [sqlalchemy] Occasional InvalidRequestError: Table 'xxx' is already defined for this MetaData instance.
OK what's idm_rw.py, and is it the only module in the app that specifies a
table named attribute_config? is idm_rw.py always imported right when the
app starts up? or is there some kind of loading going on ?
On Oct 21, 2013, at 9:51 PM, Joseph Casale jcas...@gmail.com wrote:
Hey Michael,
For reasons beyond my control at the moment, logging was utterly butchered in
a completely
incomprehensible means by another developer.
Traceback (most recent call last):
File D:\app_folder\plugin\idm_rw.py, line 6, in module
from idm_config import Attribute, Session
File D:\app_folder\include\idm_config.py, line 478, in module
class PortalConfig(Base, EnvironmentMixin):
File D:\Python33\lib\site-packages\sqlalchemy\ext\declarative\api.py,
line 50, in __init__
_as_declarative(cls, classname, cls.__dict__)
File D:\Python33\lib\site-packages\sqlalchemy\ext\declarative\base.py,
line 222, in
_as_declarative **table_kw)
File D:\Python33\lib\site-packages\sqlalchemy\schema.py, line 319, in
__new__ existing Table object. % key)
sqlalchemy.exc.InvalidRequestTable 'attribute_config' is already
defined for this MetaData instance. Specify 'extend_existing=True' to
redefine
options and columns on an existing Table object.
I think thats what it looked like before he had his way:)
Thanks!
jlc
On Mon, Oct 21, 2013 at 3:25 PM, Michael Bayer mike...@zzzcomputing.com
wrote:
how about a stack trace?
On Oct 21, 2013, at 4:11 PM, Joseph Casale jcas...@gmail.com wrote:
Hi Michael,
I spoke with the developer of the application that launches the plugins I am
writing and each
python script is run by starting an entirely new process with the
interpreter and each plugin.
It should be a clean environment. From the plugins, I simply import which
ever tables from
the module below that I would need.
In the event I am doing something wrong, my code looks like:
from os import path
from sqlalchemy import (
Column, CheckConstraint, DDL, ForeignKey, Index, Integer, String,
create_engine, event
)
from sqlalchemy.engine import Engine
from sqlalchemy.ext.declarative import declared_attr, declarative_base
from sqlalchemy.orm import sessionmaker
db_name = path.join('path', 'config', 'sqlite.db')
engine = create_engine('sqlite:///{}'.format(db_name), echo=False)
Session = sessionmaker(bind=engine, autoflush=False, autocommit=False)
Base = declarative_base()
@event.listens_for(Engine, 'connect')
def set_sqlite_pragma(dbapi_connection, connection_record):
cursor = dbapi_connection.cursor()
cursor.execute('PRAGMA foreign_keys=ON')
cursor.close()
table defs...
if __name__ == '__main__':
Base.metadata.create_all(engine)
Thanks so much for the help,
jlc
On Sun, Oct 20, 2013 at 11:01 PM, Michael Bayer mike...@zzzcomputing.com
wrote:
the MetaData object holds one Table object per unique name given. If you
use the Table constructor more than once with the same name and the same
MetaData, you get this error.
That's how the error is caused, then the fact that the error is occasional
points strongly to a race condition of some kind, more than one thread both
calling the constructor for Table with the same name. Patterns that could
cause this could be some kind of unsynchronized global registry or singleton
object that when called produces a new Table object.
The recommended pattern is for Table objects (as well as mapped classes) to
generally be declared at the module level so that these names are produced
only at module import time, which itself should occur before the application
starts any threads in addition to the main application thread.
On Oct 20, 2013, at 11:04 PM, Joseph Casale jcas...@gmail.com wrote:
I have a module that is imported by several Python scripts run by an
application
that fires up a new interpreter session for each invocation. When not under
load or
running the code manually at the cli things work fine but once the
concurrency
raises and the application starts seeing some load it emits
InvalidRequestError
exceptions on one table.
After searching I am not sure the results relate to my issue or maybe my
lack
of familiarity with SQLAlchemy has the better of me.
Any guidance would be greatly appreciated,
jlc
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