[sqlalchemy] could not assemble any primary key columns for mapped table '...'
How do I create an ORM type with no primary key columns? For some reason I'm getting: sqlalchemy.exc.ArgumentError: Mapper Mapper|ActorActivity|actor_activities could not assemble any primary key columns for mapped table 'actor_activities' for: class ActorActivity(Base): __tablename__ = 'actor_activities' actor_id = Column(UUID,ForeignKey(Actor.id), nullable = False) t= Column(SmallInteger, nullable = False) ts= Column(TIMESTAMP, nullable = False) a = Column(UUID,ForeignKey(A.id)) b = Column(UUID,ForeignKey(B.id)) n = Column(SmallInteger) x = Column(SmallInteger) Thanks for any hints. -- Yang Zhang http://yz.mit.edu/ -- 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] Custom UUID type with variant impl
I defined a TypeDecorator with impl=postgres.PGUuid so that I can work with raw UUID bytes (instead of hex strings), but I'd like to make this portable to other DBMSs, where i want the impl to be a BLOB. How can I do this? The reference docs are pretty sparse here. Thanks in advance. -- Yang Zhang http://yz.mit.edu/ -- 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] Custom UUID type with variant impl
On Thu, May 20, 2010 at 8:06 PM, Michael Bayer mike...@zzzcomputing.com wrote: On May 20, 2010, at 4:49 PM, Yang Zhang wrote: I defined a TypeDecorator with impl=postgres.PGUuid so that I can work with raw UUID bytes (instead of hex strings), but I'd like to make this portable to other DBMSs, where i want the impl to be a BLOB. How can I do this? The reference docs are pretty sparse here. Thanks in advance. i'd recommend a VARCHAR for a uuid as they are usually used as primary keys - BLOBs make very poor primary keys. But is there a way to accomplish this such that for PG dialects I'm using a PGUuid instead of a CHAR? -- Yang Zhang http://yz.mit.edu/ -- 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] could not assemble any primary key columns for mapped table '...'
On Thu, May 20, 2010 at 8:09 PM, Michael Bayer mike...@zzzcomputing.com wrote: On May 20, 2010, at 5:51 PM, Yang Zhang wrote: How do I create an ORM type with no primary key columns? For some reason I'm getting: sqlalchemy.exc.ArgumentError: Mapper Mapper|ActorActivity|actor_activities could not assemble any primary key columns for mapped table 'actor_activities' for: class ActorActivity(Base): __tablename__ = 'actor_activities' actor_id = Column(UUID, ForeignKey(Actor.id), nullable = False) t = Column(SmallInteger, nullable = False) ts = Column(TIMESTAMP, nullable = False) a = Column(UUID, ForeignKey(A.id)) b = Column(UUID, ForeignKey(B.id)) n = Column(SmallInteger) x = Column(SmallInteger) Thanks for any hints. the orm has to be given the list of columns that serve as the primary key even if the table doesn't actually have any. FAQ entry here: http://www.sqlalchemy.org/trac/wiki/FAQ#IhaveaschemawheremytabledoesnthaveaprimarykeycanSAsORMhandleit I did see that, and the only thing I'll say here is: I know what I'm doing :) although here you can just put primary_key=True on those columns you'd like to consider as PK cols, since you are using declarative and everything is in one place anyway. if the issue is, you want no PK at all, even a python-only one, that's not really possible. The ORM needs a way to locate the row for your instance in the DB in order to issue updates/deletes etc. Thanks for the anwser. It would be nice if this restriction could be lifted if explicitly requested somehow (__use_pk__ = False, and have those operations raise run-time exceptions if attempted). (As for why I'm using the ORM, it's basically because it affords many relatively minor benefits such as packaging up the tuple in its own object, a cleaner declaration syntax than Table(...), no need to use table.c.blah, custom constructors and methods, etc.) -- Yang Zhang http://yz.mit.edu/ -- 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] Custom UUID type with variant impl
Thanks for your follow-up answers to my questions (and in the other thread). I am curious about what you said on BLOBs making for poor PKs. Can you elaborate on that and/or point me to something that does? Thanks in advance. On Thu, May 20, 2010 at 8:06 PM, Michael Bayer mike...@zzzcomputing.com wrote: On May 20, 2010, at 4:49 PM, Yang Zhang wrote: I defined a TypeDecorator with impl=postgres.PGUuid so that I can work with raw UUID bytes (instead of hex strings), but I'd like to make this portable to other DBMSs, where i want the impl to be a BLOB. How can I do this? The reference docs are pretty sparse here. Thanks in advance. i'd recommend a VARCHAR for a uuid as they are usually used as primary keys - BLOBs make very poor primary keys. impl is like: class GUIDType(TypeDecorator): impl = sa.CHAR def __init__(self): TypeDecorator.__init__(self, length=16) def load_dialect_impl(self, dialect): if dialect.name == 'sqlite': return dialect.type_descriptor(sa.CHAR(self.impl.length)) else: return dialect.type_descriptor(pg.UUID()) def process_bind_param(self, value, dialect): if value is None: return value else: return str(value) def process_result_value(self, value, dialect): if value is None: return value else: return uuid.UUID(value) -- Yang Zhang http://yz.mit.edu/ -- 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. -- 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. -- Yang Zhang http://yz.mit.edu/ -- 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] BLOB and str comparisons
I'm trying to run the following: session.query(Activity).filter(Activity.blob == blob).one() where Activity.blob is a BLOB and blob is a Python bytes object (equiv. to str in Python 2.x). But although I can insert Activity(blob = blob) objects fine, the above query fails with: ProgrammingError: (ProgrammingError) You must not use 8-bit bytestrings unless you use a text_factory that can interpret 8-bit bytestrings (like text_factory = str). This is because blob has to be wrapped with sqlite3.Binary(blob). Why doesn't sqlalchemy automatically do this casting, given that it has schema awareness? Is there any way to avoid having to do this for every such query? Thanks in advance. -- Yang Zhang http://yz.mit.edu/ -- 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: BLOB and str comparisons
On Fri, May 21, 2010 at 6:47 PM, Yang Zhang yanghates...@gmail.com wrote: I'm trying to run the following: session.query(Activity).filter(Activity.blob == blob).one() where Activity.blob is a BLOB and blob is a Python bytes object (equiv. to str in Python 2.x). But although I can insert Activity(blob = blob) objects fine, the above query fails with: ProgrammingError: (ProgrammingError) You must not use 8-bit bytestrings unless you use a text_factory that can interpret 8-bit bytestrings (like text_factory = str). This is because blob has to be wrapped with sqlite3.Binary(blob). Why doesn't sqlalchemy automatically do this casting, given that it has schema awareness? Is there any way to avoid having to do this for every such query? Thanks in advance. -- Yang Zhang http://yz.mit.edu/ Also, how do I do the wrapping portably? For sqlite3 I have to wrap with sqlite3.Binary, for postgresql I have to wrap with psycopg2.Binary, etc. -- Yang Zhang http://yz.mit.edu/ -- 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] Re: BLOB and str comparisons
On Sat, May 22, 2010 at 4:12 PM, Michael Bayer mike...@zzzcomputing.com wrote: On May 22, 2010, at 1:14 AM, Michael Bayer wrote: On May 21, 2010, at 10:04 PM, Yang Zhang wrote: Also, how do I do the wrapping portably? For sqlite3 I have to wrap with sqlite3.Binary, for postgresql I have to wrap with psycopg2.Binary, etc. I am not able to reproduce your error in py2k or py3k: clarifying, I can't reproduce in py3k because the type of bytes is coerced into LargeBinary. I *can* reproduce in py2k using a non-ascii value, as the right side of the expression isn't coerced by the left, and we only see str or unicode as the type which doesn't by itself get coerced into a _Binary. So I have added an expression coercion rule to the _Binary in r19922de7317c to fix this issue. -- 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. Ah, I was *just* about to paste you a test case I constructed. Glad to see this get fixed, really appreciate it. -- Yang Zhang http://yz.mit.edu/ -- 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] What is a good pattern for using sqlalchemy+psycopg2+gevent in a pylons app
On Fri, Jun 4, 2010 at 7:16 AM, afrotypa ovuaia...@gmail.com wrote: Hi All, For a while I have been toying with the idea of developing/running a database (postgresql backend) driven WSGI app using an async python WSGI server such as gevent. Now that the newer psycopg2 (=2.2.0) drivers provide coroutine support (via a hook which makes c extension database drivers co- routine friendly) I am looking to try gevent out as soon as I can figure out how to integrate gevent and sqlalchemy. In theory it should be possible to run blocking SQLAlchemy queries in a spawned greenlet using an async DB API 2.0 driver such as psycopg2. Blocking only the greenlet handling the specific request. See the following URL for details of coroutine support in psycopg2:- http://bitbucket.org/dvarrazzo/psycogreen/wiki/Home An example of a wait call back implementation for gevent is here :- http://bitbucket.org/dvarrazzo/psycogreen/src/tip/gevent/psyco_gevent.py My question is what is a good pattern for using SQLAlchemy with a co- routine library such as gevent in a pylons based WSGI app.? For starters how do I configure the SQLAlchemy connection pool to create async connections only?. i.e. Write a custom getconn method and passing async=True to psycopg2.connect? Or pass connect_args to create_engine?. Assuming gevent spawns a greenlet to handle each WSGI request, I think SQLAlchemy should just work as usual in this situation, since the scopedSession would ensure that a different SQLAlchemy session is used for each request. Is this a reasonable assumption to make about this?. If I wanted to run multiple independent queries (each in its own greenlet) in the same pylons request, it appears I would have to explicitly create an sqlalchemy session for each greenlet instance in this case. Is this the case? Am I missing something very important here? Hopefully someone here might be able to shed some more light into all this. Thanks, Note: I already posted this question on pylons-discuss, but I am thinking this is more an SQLAlchemy than a pylons question. -- 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. I would also love to know the answer to this question! Also interested in other libraries like those for mysql (gevent-mysql). -- Yang Zhang http://yz.mit.edu/ -- 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] Getting ORM to use locking selects (select for update, etc.)
How do I get the ORM to use locking selects when I do a Session.query()? E.g., select for update, or select for share (PG)/select lock in share mode (MySQL). I know this is possible using the lower-level SQL expression library. Thanks in advance. -- Yang Zhang http://yz.mit.edu/ -- 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] What is a good pattern for using sqlalchemy+psycopg2+gevent in a pylons app
On Fri, Jun 25, 2010 at 6:41 AM, Michael Bayer mike...@zzzcomputing.com wrote: That's as deep as my thought goes on this and its all based on hypotheticals since I've never used twisted or greenlets or anything like that. Sorry if I'm totally off on how gevent/greenlets work, the linked documents didn't really make it clear how they work for someone who isn't already familiar. That's completely fair, the docs leave a lot to be desired. Think of greenlets as an implementation of cooperative threading. In typical threading, threads can first of all run in parallel, and the threading is also preemptive, meaning context switches between threads can happen at any time. With greenlets, threads are run in a single real OS thread (no parallelism, only multiplexed concurrency), and context switches between threads happen only voluntarily. Why is this useful? Because then you can write non-blocking code in a blocking style. Non-blocking IO is useful for scalable systems development, but event-driven programming (a la twisted) tends to be more tedious and less natural than programming with blocking IO. Plus, most existing code is written against blocking IO, but event-driven programming makes those difficult to reuse. So to answer your first question of what things would look like in an asynchronous world: with cooperative threads like greenlets, everything would hopefully look identical. Embracing event-driven style would indeed spell out significant changes to both sqlalchemy and user code (and that's also not what I'm personally interested in using). Upon closer inspection, it seems that changes might not even be necessary for sqlalchemy, since one can globally set the asynchronous callback for psycopg to hook directly into gevent. http://bitbucket.org/dvarrazzo/psycogreen/src/tip/gevent/psyco_gevent.py -- Yang Zhang http://yz.mit.edu/ -- 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] Getting ORM to use locking selects (select for update, etc.)
On Fri, Jun 25, 2010 at 6:42 AM, Michael Bayer mike...@zzzcomputing.com wrote: On Jun 25, 2010, at 3:27 AM, Yang Zhang wrote: How do I get the ORM to use locking selects when I do a Session.query()? E.g., select for update, or select for share (PG)/select lock in share mode (MySQL). I know this is possible using the lower-level SQL expression library. Thanks in advance. use query.with_lockmode(). The argument is passed down to the for_update argument of select(). -- 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. Thanks. Is there some way to have sqlalchemy always attach *at least* a for share/lock in share mode when issuing queries? -- Yang Zhang http://yz.mit.edu/ -- 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] ObjectDeletedError on orm.Query.delete
We're getting a strange ObjectDeletedError that we've been trying to debug for a large part of the day. The problem occurs when we keep a (hard) reference to an ORM object, drop_all, create_all, then delete() on a query over that ORM class (using the same scoped_session). Unfortunately, just the above steps aren't enough; despite our efforts so far, we haven't been able to reproduce this outside of our (large) application. Any help would be tremendously appreciated. Traceback (most recent call last): ... File /home/yang/work/app.py, line 3115, in foo count = q.delete() File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/query.py, line 1858, in delete if issubclass(cls, target_cls) and eval_condition(obj)] File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 60, in evaluate value = sub_evaluate(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 60, in evaluate value = sub_evaluate(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 60, in evaluate value = sub_evaluate(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 60, in evaluate value = sub_evaluate(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 60, in evaluate value = sub_evaluate(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 60, in evaluate value = sub_evaluate(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 60, in evaluate value = sub_evaluate(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 82, in evaluate left_val = eval_left(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/evaluator.py, line 42, in lambda return lambda obj: get_corresponding_attr(obj) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/attributes.py, line 159, in __get__ return self.impl.get(instance_state(instance), instance_dict(instance)) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/attributes.py, line 377, in get value = callable_(passive=passive) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/state.py, line 268, in __call__ self.manager.deferred_scalar_loader(self, toload) File /usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/mapper.py, line 2097, in _load_scalar_attributes raise orm_exc.ObjectDeletedError(Instance '%s' has been deleted. % state_str(state)) ObjectDeletedError: Instance 'Blah at 0x33032d0' has been deleted. When echoing the SQL, we see toward the end: ... sqlalchemy.engine.base.Engine.0x...1f90: INFO: DELETE FROM blah WHERE blah.actor_id = ? AND blah.atype = ? AND blah.domain = ? AND ... sqlalchemy.engine.base.Engine.0x...1f90: INFO: (read-only buffer for 0x4aaece0, size -1, offset 0 at 0x4807170, 2, u'fake.com', ...) sqlalchemy.engine.base.Engine.0x...1f90: INFO: SELECT blah.id AS blah_id, blah.actor_id AS blah_actor_id, blah.domain AS blah_domain, ... FROM blah WHERE blah.id = ? sqlalchemy.engine.base.Engine.0x...1f90: INFO: (426,) sqlalchemy.engine.base.Engine.0x...1f90: INFO: ROLLBACK -- Yang Zhang http://yz.mit.edu/ -- 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] Read-only transactions
Hi, we're building an application where we're distinguishing strictly between read-only and read-write transactions, so we'd like to (as a sanity measure) ensure that we're not inadvertently doing any writing from the read-only sections. What's the simplest way to catch writes with sqlalchemy? Some Googling turned up monkey-patching the .flush() method to be a no-op that also logs a message, but we're interested in raising an exception if the flush actually has dirty data to write. Thanks! -- Yang Zhang http://yz.mit.edu/ -- 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] Read-only transactions
Thanks, Michael. We're now doing something similar to your suggestion: monkey-patching Session.flush() to check len(Session.dirty) == 0. This seems to work OK. We can't rely on read-only DB-level users because we also use sqlite for testing purposes, and we'd like to catch errors there too (impractical to make our web application straddle two different Linux users). SessionExtension is interesting, but it seems there's no way to pass information to it, e.g. to let it know whether we're in a read-only transaction or not. We could switch off between two Sessions - one read-only and the other read-write - but we'd like to avoid having to keep around for each web app thread multiple Sessions (and thus 2x the open connections on the DB). Yang On Fri, Nov 5, 2010 at 6:42 PM, Michael Bayer mike...@zzzcomputing.com wrote: On Nov 5, 2010, at 8:48 PM, Yang Zhang wrote: Hi, we're building an application where we're distinguishing strictly between read-only and read-write transactions, so we'd like to (as a sanity measure) ensure that we're not inadvertently doing any writing from the read-only sections. What's the simplest way to catch writes with sqlalchemy? Some Googling turned up monkey-patching the .flush() method to be a no-op that also logs a message, but we're interested in raising an exception if the flush actually has dirty data to write. The traditional approach to this would be to connect the read-only session to an engine that's on a user with read-only permissions. From within SQLA, I suppose a before_flush() extension would fit the bill here, if new, dirty, deleted aren't empty, raise. If you want to be more fine grained about it and not trigger for attributes with no net changes, scan through dirty and see if session.is_modified(obj) returns True. Thanks! -- Yang Zhang http://yz.mit.edu/ -- 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. -- 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. -- Yang Zhang http://yz.mit.edu/ -- 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] Quick question on fetch batch size
When reading objects like so (notice no `.all()`): for obj in Session().query(User): ... what's the batch size with which sqlalchemy fetches rows from the DB? (If the engine matters: for Postgresql, MySQL, and sqlite?) Thanks. -- Yang Zhang http://yz.mit.edu/ -- 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] Multi-get?
Is there something similar to the .get() method in SqlSoup and Session but which allows me to fetch more than one object by ID, so as to save on round trips to the DB? (This could be done by composing using the IN operator in SQL.) Thanks in advance. -- Yang Zhang http://yz.mit.edu/ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@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] Multi-get?
Yeah, that's what we do right now. On Wed, Jan 26, 2011 at 8:03 PM, Mike Conley mconl...@gmail.com wrote: On Wed, Jan 26, 2011 at 8:17 PM, Yang Zhang yanghates...@gmail.com wrote: Is there something similar to the .get() method in SqlSoup and Session but which allows me to fetch more than one object by ID, so as to save on round trips to the DB? (This could be done by composing using the IN operator in SQL.) Thanks in advance. Did you try something like session.query(MyClass).filter(MyClass.id.in_([...list of ids...])).all() -- Mike Conley -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@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. -- Yang Zhang http://yz.mit.edu/ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@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] Advice on debugging an unexpected dirty flush update
I have a model with a field:
class Obj(Base):
...
meta = Column(PickleType)
For some reason, when I do
obj = session.query(Obj).get(id)
obj2 = session.query(Obj2)
I get a dirty UPDATE being attempted on the first object (noticed this
due to read-only access to a Postgresql DB):
InternalError: (InternalError) transaction is read-only
'UPDATE intel.opportunity_runs SET meta=%(meta)s WHERE
intel.opportunity_runs.id = %(intel_opportunity_runs_id)s' {'meta':
psycopg2._psycopg.Binary object at 0x2f8fe18,
'intel_opportunity_runs_id': '21da68c8-499d-11e0-a5c9-12313f00dc12'}
I'm using 0.6.4. I haven't been able to repro this issue outside the
app. Just wondering if there's any high-level tips on how to best go
about debugging this. Thanks in advance.
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Re: [sqlalchemy] Advice on debugging an unexpected dirty flush update
On Wed, Mar 9, 2011 at 7:46 AM, Michael Bayer mike...@zzzcomputing.com wrote:
On Mar 9, 2011, at 4:57 AM, Yang Zhang wrote:
I have a model with a field:
class Obj(Base):
...
meta = Column(PickleType)
For some reason, when I do
obj = session.query(Obj).get(id)
obj2 = session.query(Obj2)
I get a dirty UPDATE being attempted on the first object (noticed this
due to read-only access to a Postgresql DB):
InternalError: (InternalError) transaction is read-only
'UPDATE intel.opportunity_runs SET meta=%(meta)s WHERE
intel.opportunity_runs.id = %(intel_opportunity_runs_id)s' {'meta':
psycopg2._psycopg.Binary object at 0x2f8fe18,
'intel_opportunity_runs_id': '21da68c8-499d-11e0-a5c9-12313f00dc12'}
I'm using 0.6.4. I haven't been able to repro this issue outside the
app. Just wondering if there's any high-level tips on how to best go
about debugging this. Thanks in advance.
It would appear that the comparison of the pickled data is coming up as
modified, which is a common occurrence. To debug this, you'd do a pdb or
print statement after obj is loaded, assuming that's the one being marked
dirty, then do an obj in session.dirty which would probably return True,
then if still unsure that it's meta do an attributes.get_history(obj,
meta) and inspect the history object. Within get_history() the comparison
is actually performed. By default the == operator is used, as defined by
the compare_values() method of the column's type object. The History
object returns a tuple with ([new value], (), [previous value]), the
previous value being a copy of the original. If new_value !=
previous_value, that is the issue.
Going forward, just generally, if you see UPDATEs coming out for no reason
and you see a PickleType, its already obvious that this is the issue.
mutable types are headed towards deprecation in favor of the mutable
scalars extension in 0.7. The strategies, in order of preference are:
1. set mutable=False on the PickleType. Your CPU will thank you as
mutable=True is extremely inefficient.
2. If in place mutation detection is definitely needed, if possible (I
know, its probably not, just go to #3), upgrade to 0.7 and use the new
mutable scalars extension to detect in-place change events.
3. add a comparator function to your PickleType, or implement an __eq__()
method on the object that you're pickling.
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Ah, after some more experimentation, I think I understand what you're
saying. I can repro this problem outside the app by trying to pickle
something whose instances don't implement __eq__ (e.g., object()).
For posterity, my guess from reading the docs on MutableType (correct
me if I'm wrong) is that the ORM does loads(meta) twice, once for the
historic instance and once for the instance the app uses/mutates (not
really sure where in the code these take place), and it compares the
two whenever does a check for anything dirty to flush (which may be
pretty frequently, e.g. on every read).
And it sounds like in 0.7 the mutable scalars approach is to
define/use your own data structures that know when they've been
mutated and inform Mutable.changed().
Thanks!
--
Yang Zhang
http://yz.mit.edu/
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Re: [sqlalchemy] Advice on debugging an unexpected dirty flush update
On Wed, Mar 9, 2011 at 12:07 PM, Yang Zhang yanghates...@gmail.com wrote:
On Wed, Mar 9, 2011 at 7:46 AM, Michael Bayer mike...@zzzcomputing.com
wrote:
On Mar 9, 2011, at 4:57 AM, Yang Zhang wrote:
I have a model with a field:
class Obj(Base):
...
meta = Column(PickleType)
For some reason, when I do
obj = session.query(Obj).get(id)
obj2 = session.query(Obj2)
I get a dirty UPDATE being attempted on the first object (noticed this
due to read-only access to a Postgresql DB):
InternalError: (InternalError) transaction is read-only
'UPDATE intel.opportunity_runs SET meta=%(meta)s WHERE
intel.opportunity_runs.id = %(intel_opportunity_runs_id)s' {'meta':
psycopg2._psycopg.Binary object at 0x2f8fe18,
'intel_opportunity_runs_id': '21da68c8-499d-11e0-a5c9-12313f00dc12'}
I'm using 0.6.4. I haven't been able to repro this issue outside the
app. Just wondering if there's any high-level tips on how to best go
about debugging this. Thanks in advance.
It would appear that the comparison of the pickled data is coming up as
modified, which is a common occurrence. To debug this, you'd do a pdb or
print statement after obj is loaded, assuming that's the one being marked
dirty, then do an obj in session.dirty which would probably return True,
then if still unsure that it's meta do an attributes.get_history(obj,
meta) and inspect the history object. Within get_history() the
comparison is actually performed. By default the == operator is used, as
defined by the compare_values() method of the column's type object. The
History object returns a tuple with ([new value], (), [previous value]), the
previous value being a copy of the original. If new_value !=
previous_value, that is the issue.
Going forward, just generally, if you see UPDATEs coming out for no reason
and you see a PickleType, its already obvious that this is the issue.
mutable types are headed towards deprecation in favor of the mutable
scalars extension in 0.7. The strategies, in order of preference are:
1. set mutable=False on the PickleType. Your CPU will thank you as
mutable=True is extremely inefficient.
2. If in place mutation detection is definitely needed, if possible (I
know, its probably not, just go to #3), upgrade to 0.7 and use the new
mutable scalars extension to detect in-place change events.
3. add a comparator function to your PickleType, or implement an __eq__()
method on the object that you're pickling.
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Ah, after some more experimentation, I think I understand what you're
saying. I can repro this problem outside the app by trying to pickle
something whose instances don't implement __eq__ (e.g., object()).
For posterity, my guess from reading the docs on MutableType (correct
me if I'm wrong) is that the ORM does loads(meta) twice, once for the
historic instance and once for the instance the app uses/mutates (not
really sure where in the code these take place), and it compares the
two whenever does a check for anything dirty to flush (which may be
pretty frequently, e.g. on every read).
And it sounds like in 0.7 the mutable scalars approach is to
define/use your own data structures that know when they've been
mutated and inform Mutable.changed().
Thanks!
--
Yang Zhang
http://yz.mit.edu/
Also, when using mutable=False, is there a way to manually mark the
field dirty, without creating a new copy of the value with a different
id?
--
Yang Zhang
http://yz.mit.edu/
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[sqlalchemy] ORM performance
We've been finding the SA ORM to be a large component in our application execution time. Our application makes frequent queries, and most of them simply query whole rows from a single table with some filters, but no joins (therefore, very basic queries). We've found that an alarming amount of CPU time is being spent on three parts: 1. Query compilation. Even though the compiled_cache execution option exists, the way Query objects are commonly constructed makes compiled statements non-cacheable. For example, the statements created often have the argument values baked in, and in any case, compiled_cache is keyed by instance-equality statements, so unless we pass in the exact same statement, we have to compile again. We hacked around this by manually managing statement instances for some subset of our most common queries so that they can be looked up by compiled_cache. This resulted in ~2x improvement. 2. Instance mapping. For these same relatively simple queries that don't need fancy mapping but are run over tables with a lot of columns, it takes a long time to create the ORM instances from rows. We worked around this by adding our own MapperExtension with a populate_instance that runs much faster, but makes several assumptions (single-table, all columns, etc.). This resulted in ~2x improvement after applying 1. 3. ResultMetaData creation. Since our tables have a lot of columns, a significant amount of time is actually spent in creating processors that read data off the cursor. This work is sadly not reused in between queries. We hacked around this by building our own dialect execution_ctx_cls that caches ResultMetaData._keymap/keys for certain queries. This resulted in ~3x performance improvement after applying 1 and 2. All this feels like a lot of work, and we can't help but feel that we might be doing something wrong or missing something obvious. We're wondering if there are any tips or anything built in to SA that could help improve the performance situation. Thanks! -- Yang Zhang http://yz.mit.edu/ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@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] Postgresql COPY
Is it possible to execute a Postegresql COPY ... FROM STDIN statement via sqlalchemy, or do we have to drop down to psycopg2 for that (http://initd.org/psycopg/docs/usage.html#using-copy-to-and-copy-from)? Tried executing a COPY statement followed directly by the input values, as in psql, but that didn't work. Thanks in advance. -- Yang Zhang http://yz.mit.edu/ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@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] ORM performance
On Wed, Apr 13, 2011 at 6:07 PM, Michael Bayer mike...@zzzcomputing.com wrote:
To work around the instance arguments being baked in, create the query like
this:
query.filter(SomeClass.somerecord ==bindparam(somerecord))
The params are then added using query.params(somerecord=x).
Is it possible to use this with .get()?
Currently, all our
...query(Item).get(id)
become
q=...query(Item).filter_by(id=bindparam('id'))
q.params(id=id).one()
We're thinking of having a custom Session and Query that override
Query.get() to build and cache the above query internally, since this
is such a frequently used construct. But we wanted to see if we're
missing anything first.
--
Yang Zhang
http://yz.mit.edu/
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Re: [sqlalchemy] ORM performance
On Tue, Apr 26, 2011 at 12:32 PM, Yang Zhang yanghates...@gmail.com wrote:
On Wed, Apr 13, 2011 at 6:07 PM, Michael Bayer mike...@zzzcomputing.com
wrote:
To work around the instance arguments being baked in, create the query
like this:
query.filter(SomeClass.somerecord ==bindparam(somerecord))
The params are then added using query.params(somerecord=x).
Is it possible to use this with .get()?
Currently, all our
...query(Item).get(id)
become
q=...query(Item).filter_by(id=bindparam('id'))
q.params(id=id).one()
We're thinking of having a custom Session and Query that override
Query.get() to build and cache the above query internally, since this
is such a frequently used construct. But we wanted to see if we're
missing anything first.
Actually, this is turning out *slower* than using .get(), by about an
order of magnitude.
--
Yang Zhang
http://yz.mit.edu/
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[sqlalchemy] Query object over sqlite3 returning Nones
I'm using sqlalchemy 0.6.6 and sqlite 3.6.22 on Python 2.6. When I do: In [1]: for i in ses.query(UserSnapshot): ...: print i ...: if i is None: break ...: I see: ... twopt.UserSnapshot object at 0x86a52f50 twopt.UserSnapshot object at 0x86a55050 twopt.UserSnapshot object at 0x86a55110 twopt.UserSnapshot object at 0x86a551d0 twopt.UserSnapshot object at 0x86a55290 twopt.UserSnapshot object at 0x86a55350 None My schema: class User(Base): __tablename__ = 'user' id = Column(Integer, primary_key=True) blob = Column(LargeBinary, nullable=False) since = Column(DateTime, nullable=False) class UserSnapshot(Base): __tablename__ = 'user_snapshot' id = Column(Integer, primary_key=True) uid = Column(Integer, ForeignKey(User.id), nullable=False) blob = Column(LargeBinary, nullable=False) time = Column(DateTime, nullable=False) Short of dumping my entire DB, any hints as to what might cause `None` to be returned? I searched the documentation but couldn't find any leads. Thanks. -- Yang Zhang http://yz.mit.edu/ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@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: Query object over sqlite3 returning Nones
Oy...this turned out to be due to my own fiddling with the DB outside of sqlalchemy, where I swapped out the user_snapshot table with a copy that had id int primary key instead of id integer primary key Apparently sqlite treats these differently: sqlite create table a (a integer primary key, b integer); sqlite insert into a (b) values (0); sqlite select * from a; 1|0 sqlite create table b (a int primary key, b integer); sqlite insert into b (b) values (0); sqlite select * from b; |0 I couldn't find in http://www.sqlite.org/autoinc.html or http://www.sqlite.org/datatype3.html any mention of this peculiar distinguishing behavior. Anyway, that's that. On Fri, Nov 18, 2011 at 4:45 PM, Yang Zhang yanghates...@gmail.com wrote: I'm using sqlalchemy 0.6.6 and sqlite 3.6.22 on Python 2.6. When I do: In [1]: for i in ses.query(UserSnapshot): ...: print i ...: if i is None: break ...: I see: ... twopt.UserSnapshot object at 0x86a52f50 twopt.UserSnapshot object at 0x86a55050 twopt.UserSnapshot object at 0x86a55110 twopt.UserSnapshot object at 0x86a551d0 twopt.UserSnapshot object at 0x86a55290 twopt.UserSnapshot object at 0x86a55350 None My schema: class User(Base): __tablename__ = 'user' id = Column(Integer, primary_key=True) blob = Column(LargeBinary, nullable=False) since = Column(DateTime, nullable=False) class UserSnapshot(Base): __tablename__ = 'user_snapshot' id = Column(Integer, primary_key=True) uid = Column(Integer, ForeignKey(User.id), nullable=False) blob = Column(LargeBinary, nullable=False) time = Column(DateTime, nullable=False) Short of dumping my entire DB, any hints as to what might cause `None` to be returned? I searched the documentation but couldn't find any leads. Thanks. -- Yang Zhang http://yz.mit.edu/ -- Yang Zhang http://yz.mit.edu/ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@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] AttributeError: 'Session' object has no attribute '_model_changes'
Specifically, the code path where this is appearing ends up looking like:
session = sqlalchemy.orm.Session(sqlalchemy.create_engine('sqlite:///'))
session.execute('run_some_transaction()')
session.commit()
This raises:
AttributeError: 'Session' object has no attribute '_model_changes'
I get that there's nothing happening at the Session layer, but how
else do I achieve this without having to duplicating my code to use
raw Connections instead of Sessions? (Most of my code *does* use
Sessions; only under certain conditions does no Session layer activity
actually take place.)
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[sqlalchemy] Re: AttributeError: 'Session' object has no attribute '_model_changes'
Sorry, disregard—wrong mailing list! This is Flask-SQLAlchemy-specific.
On Mon, Oct 21, 2013 at 11:51 PM, Yang Zhang yanghates...@gmail.com wrote:
Specifically, the code path where this is appearing ends up looking like:
session = sqlalchemy.orm.Session(sqlalchemy.create_engine('sqlite:///'))
session.execute('run_some_transaction()')
session.commit()
This raises:
AttributeError: 'Session' object has no attribute '_model_changes'
I get that there's nothing happening at the Session layer, but how
else do I achieve this without having to duplicating my code to use
raw Connections instead of Sessions? (Most of my code *does* use
Sessions; only under certain conditions does no Session layer activity
actually take place.)
--
Yang Zhang
http://yz.mit.edu/
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[sqlalchemy] Connecting via pyodbc (to Vertica)
I'm trying to connect to Vertica as a regular ODBC DSN, which I can do
fine outside of sqlalchemy:
$ isql -v pod
+---+
| Connected!|
| |
| sql-statement |
| help [tablename] |
| quit |
| |
+---+
SQL
In [4]: pyodbc.connect('DSN=pod', ansi=True)
Out[4]: pyodbc.Connection at 0x18f0440
In [6]: con.execute('select 1')
Out[6]: pyodbc.Cursor at 0x18e8c90
How do I get sqlalchemy to connect? It speaks a Postgresql-like
dialect (since it's a fork of PG); I have installed vertica-sqlalchemy
which provides this dialect. However, I'm confused because there's no
way to just specify a DSN to sqlalchemy (not even getting to the
dialect-using stage of connection). Whatever strings I try, I get:
DBAPIError: (Error) ('IM002', '[IM002] [unixODBC][Driver Manager]Data
source name not found, and no default driver specified (0)
(SQLDriverConnect)') None None
The /etc/odbc.ini is pretty simple:
[ODBC Data Sources]
pod = the pod database
[pod]
Driver = /opt/vertica/lib64/libverticaodbc.so
Servername = localhost
Database = pod
Port = 15433
UserName = dbadmin
Password = ...
I've been wrestling with this for a good part of the day. Any hints
would be greatly appreciated. Thanks in advance.
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[sqlalchemy] Re: Connecting via pyodbc (to Vertica)
Right after sending this, I hit upon the magic incantation, which I
had not thought of trying:
vertica+pyodbc://pod
Sigh.
On Fri, Nov 8, 2013 at 4:48 PM, Yang Zhang yanghates...@gmail.com wrote:
I'm trying to connect to Vertica as a regular ODBC DSN, which I can do
fine outside of sqlalchemy:
$ isql -v pod
+---+
| Connected!|
| |
| sql-statement |
| help [tablename] |
| quit |
| |
+---+
SQL
In [4]: pyodbc.connect('DSN=pod', ansi=True)
Out[4]: pyodbc.Connection at 0x18f0440
In [6]: con.execute('select 1')
Out[6]: pyodbc.Cursor at 0x18e8c90
How do I get sqlalchemy to connect? It speaks a Postgresql-like
dialect (since it's a fork of PG); I have installed vertica-sqlalchemy
which provides this dialect. However, I'm confused because there's no
way to just specify a DSN to sqlalchemy (not even getting to the
dialect-using stage of connection). Whatever strings I try, I get:
DBAPIError: (Error) ('IM002', '[IM002] [unixODBC][Driver Manager]Data
source name not found, and no default driver specified (0)
(SQLDriverConnect)') None None
The /etc/odbc.ini is pretty simple:
[ODBC Data Sources]
pod = the pod database
[pod]
Driver = /opt/vertica/lib64/libverticaodbc.so
Servername = localhost
Database = pod
Port = 15433
UserName = dbadmin
Password = ...
I've been wrestling with this for a good part of the day. Any hints
would be greatly appreciated. Thanks in advance.
--
Yang Zhang
http://yz.mit.edu/
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