Good evening Michael,
On 09/04/2012 20:05, Michael Bayer wrote:
even google is not telling me which vendor has produced this expression. Because
"computed by" is the most generic phrase.
I see a brief mention in firebird's docs ? no clue.
Sorry, should have mentioned that currently I use Firebird SQL 2.5.
BTW, it is the first FB release which supports an "alter" column to
change the computed by clause.
I'd probably use @compiles on top of CreateTable for this, and use a regular expression
to tokenize out the columns that have "computed_by" in their info field.
To really support extensions like this fully we'd have to break out compiler to
make usage of a CreateColumn directive, then you'd be able to put @compiles on
top of CreateColumn and generate the columns directly. wouldn't be too
terrible but 0.8 is quite backlogged (see
http://www.sqlalchemy.org/trac/ticket/2463).
Or why not do it at the type level ? Can you just make a UserDefinedType here
?
Will look into these.
2463 might be nicer.
and will keep watching this one in case it does make it into 0.8.
Thanks
Werner
On Apr 9, 2012, at 1:36 PM, Werner wrote:
Is there a way in SA 0.7.6 to define computed columns as part of other
DeclarativeBase columns?
Currently I do manual DDL, but would like to get things setup to be able to
easier move to another db backend.
Most of my computed columns are calculations like the one on AVAILCAPACITY
below, but also have a few simple selects like in the USEDCAPACITY column.
CREATE TABLE WINERACKIT (
WINERACKITID PKEYS NOT NULL,
SPLIT INTEGER NOT NULL,
CAPACITY INTEGER DEFAULT 0,
FK_WINERACKBID PKEYS NOT NULL /* PKEYS = BIGINT */,
USEDCAPACITY COMPUTED BY ((SELECT COUNT(BOTTAG.TAGNO) FROM BOTTAG WHERE
BOTTAG.FK_WINERACKIT_ID = WINERACKIT.ID)),
AVAILCAPACITY COMPUTED BY (CAPACITY-USEDCAPACITY)
Thanks in advance for some pointers on how to do this.
Werner
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