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 is
http://www.sqlalchemy.org/docs/session.html#embedding-sql-insert-update-expressions-into-a-flush
.
>
> 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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