Thanks. I might have figured out a solution. I can get it to assign
func.compressed to the column attribute, but I can't get it to load
the text uncompressed now.
class BaseStruct(object):
def _set_text(self, text):
self.compressed = func.compress(text)
def _get_text(self):
return select(["uncompress(compressed)"])
text = property(_get_text, _set_text)
class Matrix(BaseStruct, Base):
__tablename__ = 'matrix'
__table_args__ = (
{'autoload':True}
)
compressed = deferred(Column(Binary()))
text = BaseStruct.text
>>> s = Session()
>>> m = s.query(Matrix).get(1)
>>> m.compressed
<read-only buffer for 0x1e67000, size -1, offset 0 at 0x12e7680>
>>> m.text='Blah'
>>> m.compressed
<sqlalchemy.sql.expression.Function at 0x12e76b0; compress>
So after assigning the text... I get what I want. The column mapped
attribute is assigned func.compress(text). But I also need to
uncompress the field to read it sometimes.
>>> s = Session()
>>> m = s.query(Matrix).get(7)
>>> m.text
<sqlalchemy.sql.expression.Function at 0x1392cf0; uncompress>
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.
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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