On Feb 20, 2011, at 3:17 PM, fred.h...@mail.com wrote:
> Hello Michael,
>
> thank you (all) for sqlalchemy :)
>
> The "uniquifying" had me spooked, and i am afraid it got me confused
> completely about connections, sessions, autoflushing and all the wonderful
> toys.
I'm not really sure how uniquifying somehow has to do with sessions and
autoflushing. Imagine there's no "uniquifying". Then imagine that
query.all() just means, sorted(set([x for x in query])). Does that have some
impact on connections or otherwise ?
> I now even flush() and commit() directly after every add
that's entirely unnecessary. flush is usually automatic and commit() should
be called at the end of a transaction (and your app should have some concept of
transactions beginning and ending, just as though you made a connection to your
database, worked with it, then closed it).
> ... (not that it helped, ofc). So, lots of gratitude here for answering me on
> a sunday evening (for me). Ppl here all of a sudden thought i was going nuts.
>
> Back to it, thank you very much.
>
> cheers
>
>
> -----Original Message-----
> From: Michael Bayer <mike...@zzzcomputing.com>
> To: sqlalchemy@googlegroups.com
> Sent: Sun, Feb 20, 2011 7:30 pm
> Subject: Re: [sqlalchemy] difference between query.count() and query.all(),
> concurrency?
>
>
> On Feb 20, 2011, at 8:40 AM, fred.h...@mail.com wrote:
>
>> Hi listmembers,
>>
>> i have a problem with a difference i find playing with sqla between
> query.count and query.all results.
>> I have a parent class declaratively mapped to a table in MySQL, there
> is a child class with a relationship.
>> I'm not sure how to create a quick session (i suspect a problem lies
> there, but i have no clue) - my usecase is very general, but i am not sure if
> i have the lingo right (been reading the docs till blue in the face, didn't
> know using this wonderful stuff is so intricate).
>>
>> In short i use the following, (productdescriptions depending on
> languages):
>>
>> Session = scoped_session(sessionmaker())
>> session = Session(autoflush=True)
>>
>> class Products(Base):
>> products_id = Column(Integer, primary_key=True)
>> products_loc = Column(String)
>> product_descriptions = relationship("Products_description",
>> cascade="all",
>> backref=backref('product'))
>>
>> class Products_description(Base):
>> products_description_id = Column(Integer, primary_key=True)
>> products_id = Column(Integer, ForeignKey('products.products_id'),
> nullable=False)
>> language_id = Column(Integer, ForeignKey('languages.languages_id'),
> nullable=False)
>>
>> class Languages(Base):
>> languages_id = Column(Integer, primary_key=True)
>> etc..
>>
>>
>> I would expect the product_descriptions to hold two objects if there
> are two records in de database (for two languages, but that is irrelevant
> here .. or is it?), related via the products_id attribute. When i query the
> database like so:
>>
>> qry =
> session.query(Products_description).join(Products).filter(Products_descri
>
>> ption.products_id == :someniceproducts_id)
>>
>> with some nice existing products_id
>>
>> qry.count() results in 2L (like i would expect, there being two
> description records in the db for the product)
>>
>> but when i issue:
>> qry.all()
>>
>> i only get one object as a result.
>>
>> I clearly - after studying the docs - don't understand sqlalchemy at
> all :)
>> What am i doing wrong? it looks so easy and straightforward that i
> find myself checking my chair twice to be sure it's there before sitting down
> (..).
>
> count() is going to count rows, not necessarily distinct entities. You have
> a join in your query so you're going to get multiple Products_description
> rows with the same identifier, for each related Products. all() gets two
> rows as well internally, which you'll see if you enable echo='debug' on your
> engine, but because they have the same primary key identifier for
> Products_description they are "uniqueified" before being returned.
>
> If you queried for both, query(Products_description, Products), the
> "uniquifying" step is removed and you'd get two entries.
>
>
>
>
>
>
>
>>
>> Can somebody please HELP me :)
>> Cheers
>> Freddy
>>
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