patrick wrote:
> In the past I assigned
> Matrix.text=column_property(select(["uncompress(compressed)"]),deferred=True)
> I could probably write a little SqlSoup to do this select statement,
> but is there a way I can integrate this all well? The way I'm doing
> this feels very sloppy. SqlAlchemy is powerful, but can be very
> complicated.
you should map an attribute directly to
column_property(uncompress(table.c.compressed)). if you want it only to
fire when you read it, use deferred() instead of column_property().
>
> On Mar 5, 8:30 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
>> On Mar 5, 2010, at 6:44 PM, patrick wrote:
>>
>> > Well it's something between the two. The instance variable
>> > "compressed" will always be NULL when adding or updating an instance,
>> > but I want it to infer a value from another instance variable. When
>> > inserting... the value of 'compressed' in the sql statement needs to
>> > be the raw SQL string "COMPRESS('%s')" % instance.text. It isn't
>> > simply running it through a function... it's dynamically creating the
>> > column value from the object's instance variables upon insert or
>> > update. MySQL has some funky compression function so the insert value
>> > for the column has to be raw sql.
>>
>> so do a before_insert() mapper extension and set the attribute as needed
>> to "func.compressed(instance.text)". Or do the same at the object
>> level, i.e user sets myobject.foo, "foo" is a descriptor-enabled method
>> which then sets myobject.bar = func.compressed(foo) or whatever.
>>
>> the technique here
>> ishttp://www.sqlalchemy.org/docs/session.html#embedding-sql-insert-upda....
>>
>>
>>
>> > On Mar 4, 3:30 pm, "Michael Bayer" <mike...@zzzcomputing.com> wrote:
>> >> patrick wrote:
>> >>> Hey,
>> >>> I'm trying to create dynamic defaults for columns ala "http://
>> >>>www.sqlalchemy.org/docs/metadata.html#context-sensitive-default-funct...".
>> >>> MySQL has COMPRESS and UNCOMPRESS functions that I'm trying to
>> >>> leverage. I don't want to compress with python's zlib because I
>> have
>> >>> legacy tables that were compressed using MySQL (which has a weird
>> non-
>> >>> standard zip header and body), and I need to interface with them.
>> >>> Anyway, during an insert or update, I want to grab the 'text'
>> variable
>> >>> from the instance object and insert it into the database like:
>> >>> COMPRESS("the text value"). Obviously context.current_parameters is
>> >>> not the appropriate object, but I can't figure out if it's possible
>> to
>> >>> access the instance being inserted/updated.
>>
>> >> are you trying to create a *default* value for an INSERT/UPDATE when
>> NULL
>> >> would otherwise be passed, or are you trying to run all
>> incoming/outgoing
>> >> data through a SQL function ? those are two completely separate
>> topics.
>>
>> >>> def compress_text(context):
>> >>> return "COMPRESS('%s')" % context.current_parameters['text']
>>
>> >>> class Tree(BaseStruct, Base):
>> >>> __tablename__ = 'tree'
>> >>> __table_args__ = (
>> >>> {'autoload':True}
>> >>> )
>>
>> >>> compressed =
>> >>> deferred(Column(Binary(),default=compress_text,default=compress_text,onupdate=compress_text))
>> >>> text =
>> >>> column_property(select(["UNCOMPRESS(compressed)"]),deferred=True)
>>
>> >>> Is this possible with 0.5.7?
>>
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