[sqlalchemy] Re: Tutorial Issue
I noticed that line but didn't think it was essential. It looked more
of an aside thing, but it seems I was wrong. Anyway, I'm glad I
brought it up because someone else could have made the same mistake.
Thank you for your answer.
On Sep 30, 5:16 pm, Michael Bayer mike...@zzzcomputing.com wrote:
OK, was hard to spot, and I think maybe I should change this, there's a line
where it does this:
users_table = User.__table__
So the original users_table is replaced with the one that User.__table__ is
mapped to.
I'm going to change that remapping to read like this:
mapper(User, User.__table__, properties={
... 'addresses':relationship(Address, backref='user', cascade=all,
delete, delete-orphan)
... })
Mapper at 0x...; User
addresses_table = Address.__table__
mapper(Address, addresses_table)
Mapper at 0x...; Address
On Sep 30, 2010, at 6:22 AM, LucianU wrote:
Hello, all!
I'm following the tutorial
herehttp://www.sqlalchemy.org/docs/orm/tutorial.html
and I'm running into some problems at one moment, specifically at the
Configuring delete/delete-orphan Cascade section. Here is a paste of
exactly what I'm doinghttp://bpaste.net/show/9861/. Am I making a
mistake somewhere or is the tutorial incorrect?
Lucian
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[sqlalchemy] Passing model objects to other threads
Hi all, i'm using SQLAlchemy in a TG2 web app which has long-running jobs kicked off by user POSTs. I'm planning on writing the pending jobs to the DB, then kick off a threading.Thread at the end of the web app method to actually do the work. Question - I'll need to pass the job description (a SA object) to the child thread; but to use the description, I need to detach it from the old TG2 thread's SA session, and reattach it to the child thread's SA session, right? How best to do that? I don't see a way of getting the current session from a live SA object... Thanks! James -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Re: Passing model objects to other threads
Hi, have you considered using TGScheduler ? -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Re: Passing model objects to other threads
Hi, Yes I was going to have TGScheduler run at intervals to complete any jobs that fail the first time round (as they might, for reasons I can't control). However, the initial job run is reasonably time-sensitive, so I would like it to get started right as the user POSTs the instructions; but I was thinking that having every web app instance polling the DB at short intervals would be a lot of overhead. That said, if TGScheduler handles the session initiation gracefully, and I'm going to have it running anyway, I could get away with polling a few times a minute and the user wouldn't realistically notice... Thanks for the suggestion! If all else fails, I'll bastardise the session initialisation code from TGScheduler to roll my own :) James On Oct 1, 3:11 pm, NiL nicolas.laura...@gmail.com wrote: Hi, have you considered using TGScheduler ? -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Passing model objects to other threads
On Oct 1, 2010, at 9:40 AM, James wrote: Hi all, i'm using SQLAlchemy in a TG2 web app which has long-running jobs kicked off by user POSTs. I'm planning on writing the pending jobs to the DB, then kick off a threading.Thread at the end of the web app method to actually do the work. Question - I'll need to pass the job description (a SA object) to the child thread; but to use the description, I need to detach it from the old TG2 thread's SA session, and reattach it to the child thread's SA session, right? How best to do that? I don't see a way of getting the current session from a live SA object... If you're writing jobs to the DB anyway, why not use a different process to handle the jobs, and have it poll the jobs table, instead of passing directly ? That's how I'm currently doing it. The job runner then forks off additional procs to run N number of jobs simultaneously with multiprocessing. You at least get true concurrency that way. Otherwise, the general paradigm to pass state between threads uses merge(), it leaves the original unaffected. obj = Session.query(...).first() start_new_thread(obj) # in the thread's method: def start_my_thing(obj): obj = Session.merge(obj) -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] appropriate place for before insert
I need to make a call to an external system (through SOAP) when a new object is saved/updated/deleted. If the external call fails then I would like the save to also fail. I have looked at the documentation and a MapperExtension cannot change the flush plan to cancel if the external call fails. I have looked at session extensions and it looks like they would work, but it seems far removed from my object. I would have to check each object in the session to see if it is the correct type and then execute the external method and then remove the object from the session if it fails. Is this the recommended way of binding an external action when modifying an object? I suppose I could add a before_insert method to my object and have a session extension that just checks every object to see if it has before_insert and if it does then execute it (and any errors would remove the object from the session). Thanks, Landreville -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] appropriate place for before insert
On Oct 1, 2010, at 12:30 PM, Landreville wrote: I need to make a call to an external system (through SOAP) when a new object is saved/updated/deleted. If the external call fails then I would like the save to also fail. I have looked at the documentation and a MapperExtension cannot change the flush plan to cancel if the external call fails. I have looked at session extensions and it looks like they would work, but it seems far removed from my object. I would have to check each object in the session to see if it is the correct type and then execute the external method and then remove the object from the session if it fails. Is this the recommended way of binding an external action when modifying an object? I suppose I could add a before_insert method to my object and have a session extension that just checks every object to see if it has before_insert and if it does then execute it (and any errors would remove the object from the session). Any extension, mapper or session, can cancel the operation overall by raising an exception, which will result in halting the flush and issuing a ROLLBACK. Usually, if something goes wrong inside of a transaction, the whole thing is rolled back since you otherwise have only a partial state of data. Inside of mapper extension, a simplistic dont update the row operation may be possible if you just expired the attributes of the instance inside of before_update(), though I haven't tried this and it wouldnt really work for inserts or deletes anyway. Within session extension, its common to search for objects by traversing through the .new, .dirty and .deleted collections. 0.7 will be expanding on this model by providing event listener hooks that do this filtering for you, sending only objects of the desired type to the listener, and from that it follows that we can eventually optimize the search by improving the bookkeeping performed by these collections.SessionExtension is definitely the more generic choice overall these days for flush events. the use cases for MapperExtension are much smaller. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Re: appropriate place for before insert
On Oct 1, 12:54 pm, Michael Bayer mike...@zzzcomputing.com wrote: Any extension, mapper or session, can cancel the operation overall by raising an exception, which will result in halting the flush and issuing a ROLLBACK. Usually, if something goes wrong inside of a transaction, the whole thing is rolled back since you otherwise have only a partial state of data. Inside of mapper extension, a simplistic dont update the row operation may be possible if you just expired the attributes of the instance inside of before_update(), though I haven't tried this and it wouldnt really work for inserts or deletes anyway. Within session extension, its common to search for objects by traversing through the .new, .dirty and .deleted collections. 0.7 will be expanding on this model by providing event listener hooks that do this filtering for you, sending only objects of the desired type to the listener, and from that it follows that we can eventually optimize the search by improving the bookkeeping performed by these collections. SessionExtension is definitely the more generic choice overall these days for flush events. the use cases for MapperExtension are much smaller. Sounds good. I suppose I would most often raise an exception to rollback the entire flush, but in rare cases I might want to go ahead and save the rest of the object I would just detach one from the session and delete it. Thanks for you reply, Landreville -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Building queries programmatically
Hi,
I'm working on an application where queries are created completely by
the user. (The goal is to make it easy for the user). Because of this
I have to support dynamic query creation and manipulation. My current
model has a query class with my own created specification for queries
which is manipulated by the user via the GUI. This is then turned into
an SQLA query when it's run. Well, it will be turned into one.
I'm trying to wrap my head around building the WHERE clause. I find
that when a function returns a condition (age 18 for example) it
comes with brackets around it. However, when I enter it into the where
function directly it doesn't unless it uses an SQLA method like
column.in_(stuff) .
I have some test code I've been playing with below:
def condition(age,b):
return age b
name = tableObjects['users'].c['name']
age = tableObjects['users'].c['age']
password = tableObjects['users'].c['password']
q = select([tableObjects['users']])
names = ('Mark','Joel')
#the query construction
a = (name.in_(names))
# I enter it into the where method directly:
q = q.where(name.in_(names)+age18+~password.like('v'))
#Results in:
#WHERE (users.name IN (?, ?)) + users.age ? + (users.password NOT
LIKE ?)
# If functions build the term:
expr = name.in_(names) + condition(age,18)
q = q.where(expr) # If placed in where(expr) it results in WHERE
(users.name IN (?, ?)) + (users.age ?)
# Note extra brackets
result = dataConnections['sqlite:///tutorial.db'].execute(q)
for row in result:
print row
Would the brackets make any difference to the performance? (They
wouldn't make any meaningful difference to the result as far as I can
see)
I've recently noticed the serializer for SQLA queries. How easy would
it be to save them with IDs? Also, is it easy to manipulate and adjust
a specific piece of a query? Like, the second element of a nested
where clause? If it is, my separate class system may be unnecessary
overhead (unless I decide the ability to port to other libraries is
really important...).
Thanks,
Edward
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