[sqlalchemy] count(*) function
Hi, does anyone know the syntax of SELECT COUNT(*) FROM table_name; for SQLAlchemy? Is there a list of functions (used in SELECT statement) that exist in SQL that I can use in SQLAlchemy? btw, I am using MySQL. I need to see if my table is empty (isemty function doesn't work). Thanks! --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: count(*) function
milena wrote: I have tried select([func.count(*)], from_obj=[table_name]).execute() but it didn't work I suppore you're not using mappers, so this is the fastest method: number_of_rows = table.count().execute().fetchone()[0] where table is the table object --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: count(*) function
I have tried select([func.count(*)], from_obj=[table_name]).execute() but it didn't work I think you should try to specify a column in your count or leave it empty (didn't try). If you're using mapped objects, you can use the SelectResults extension: from sqlalchemy.ext.selectresults import SelectResults SelectResults(your_session.query(YourMappedClass)).count() Cheers, Seb -- Sébastien LELONG sebastien.lelong[at]sirloon.net --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: Column aliases
Michael Bayer wrote: to have aliases of properties that are usable with get_by(), use the synonym function, described in: http://www.sqlalchemy.org/docs/adv_datamapping.myt#advdatamapping_properties_overriding Thank you. Altough the docs are very well done, there are many APIs and that sometimes may be confusing. --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: Questions about polymorphic mappers
Micheal Bayer wrote: id rather just add another plugin point on MapperExtension for this, which takes place before the polymorphic decision stage at the top of the _instance method, like get_polymorphic_identity(). that way you could do all of this stuff cleanly in an extension (and id do that instead of making polymorphic_identity into a list). hows that sound? That would be ideal for me, and would seem to be the most flexible solution as well - it leaves the decision for which class to use up to the application. What would it actually return, though? An instance ready to be populated? Thanks a lot, Simon --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: pickle and mapped objects
Michael Bayer ha scritto:
if you can pickle the object by itself, then id guess youre using lazy
loaders with the query.options(lazyload('something')) call, which
places per-object lazy loaders (i.e. callables) on your objects.
I'm not sure, since I never use lazy loaders (I use Twisted).
either make sure the lazy loaders are fired off, or make lazyload the
default loading for that mapper. similar advice if you are using
deferred columns.
The problem can be with a nested relation (always lazy loaded, as I can
understand).
However the best solution is to implement __setstate__, also for
avoiding trash in the database.
Thanks and regards Manlio Perillo
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[sqlalchemy] Re: adding a foreign key constraint to an existing table
On 1/15/07, Michael Bayer [EMAIL PROTECTED] wrote: 2. no support for CASCADE in the DROP statement right now. someone fill me in, is DROP CASCADE part of the sql standard ? yes, at least for tables. --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] portable schema
Hi.
I don't know if this already implemented or planned.
Schemas are supported by SQLAlchemy, but unfortunately not all database
supported by SQLAlchemy supports schema.
My idea is simple.
1) When the database does not support schema, the schema name specified
in Table costructor should be prepended to the table name.
foo = Table('foo', ..., schema='bar')
result in a table named bar_foo
2) If the database is SQLite, the schema name should be used to create a
new database, attaching it to the main database.
engine = create_engine('sqlite://db')
foo = Table('foo', ..., schema='bar')
result in a new database named db_bar.
Of course the user can decide if to use solution 1)
Regards Manlio Perillo
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[sqlalchemy] Re: portable schema
On Jan 15, 2007, at 12:05 PM, Manlio Perillo wrote:
My idea is simple.
1) When the database does not support schema, the schema name
specified
in Table costructor should be prepended to the table name.
foo = Table('foo', ..., schema='bar')
result in a table named bar_foo
why not just name your table bar_foo ? why have two ways to do the
same thing ? how would this work with autoloading ? why make a
keyword argument called schema do something that is nothing like a
what a schema actually is ?
2) If the database is SQLite, the schema name should be used to
create a
new database, attaching it to the main database.
engine = create_engine('sqlite://db')
foo = Table('foo', ..., schema='bar')
result in a new database named db_bar.
why not just conenct to a database file called db_bar? why have
two ways to do the same thing ? why make a keyword argument called
schema do something that is nothing like a what a schema actually
is ?
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[sqlalchemy] Re: Questions about polymorphic mappers
at this point the entity_name should get set after your custom create_instance is called (at least thats in the trunk). init_attr is not required, it pre-sets attributes on the object that are otherwise auto-created later (but the autocreation step throws a single AttributeError per attribute, which hits performance a little bit). On Jan 15, 2007, at 12:19 PM, King Simon-NFHD78 wrote: Michael Bayer wrote: you can still override create_instance() as well and try to spit out subclasses that are otherwise not mapped. This was something I looked at a while ago as well, and I wasn't sure what the requirements on objects returned from create_instance were. If it is not overridden, the mapper calls _create_instance, which sets _entity_name and calls attribute_manager.init_attr. How important are these things to the rest of the library? Simon --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Constructing where-clauses dynamically
in continuing http://groups.google.com/group/sqlalchemy/browse_thread/thread/4dab6cfae1f62521/8b66851007c6a652?lnk=gstq=daniel+millerrnum=2#8b66851007c6a652 , which bizarrely GG will not let me continue, on a closely related but not exactly the same issue, i broke my limit of people expecting this particular behavior and just added it: # get an instance of Address someaddress = session.query(Address).get_by(street='123 Green Street') # look for User instances which have the # someaddress instance in their addresses collection l = session.query(User).select_by(addresses=someaddress) so, not quite the same as the previous discussion since we are back in the XXX_by world of things, but this would be SA's first foray into higher-level querying functionality. as ive maintained, i dont think the Query object can go too far with this since it ultimately would need some totally reworked querying paradigm to come up with some kind of OQL. --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Action on object deletion
Hi Folks, I have an application that needs to do a certain amount of housekeeping when objects are deleted or edited. Essentially, I need to keep historical data, so under some circumstances deleted objects actually need to be obsoleted, and edited objects need to be copied and references to them from elsewhere updated. Now, object modification can be caught and handled in the object itself without (too much) hassle. But object deletion through a session is another matter... My first impulse was to use a mapper extension and before_delete. This is not very satisfying, though - since before_delete is called inside a flush(), the ORM can't be used, and manipulating the database straight through the connection object during a flush() just seems brittle. Another option is to put a .delete() method on the mapped object itself, and mandate that objects should be deleted through this method. This means that these objects would need to be treated differently througout the codebase, which is not nice. That said, this is the approach I'm using at the moment. What would be nice is if a method on an object could be called when session.delete(object) is called, before the flush() happens. To do this, Session.delete might be extended to provide MapperExtension-like functionality: def delete(self, object, entity_name=None): ... if hasattr(object, on_delete): r = object.on_delete(self) if r == EXT_PASS: return ... The same thing could be done for other session.X operations on mapped objects. I'm not yet very familiar with SQLAlchemy's internals, so I'm sure there are subtleties I haven't thought of, but you get the drift. So, firstly: is there a nicer way to do this? Secondly, is a patch that does something like the above a good idea? Cheers, Aldo -- Aldo Cortesi [EMAIL PROTECTED] http://www.nullcube.com Mob: 0419 492 863 --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
