Thanks for your help, mdiperro and Yarko (thanks for the investigation of the code :) ).
Circular refererences aren't what I'm attempting at all (obviously that can't work). Instead, those fields would be left nullable and filled in later, for the most part. Example: an already created Person object reference is all that's required when creating Post object. No reference filled in in the image field in Post. Later, an Image object can be uploaded and referenced by that already created Post. Now the image field in the Post has data. What *should* I be doing to define these relationships, for best practices? (if this does not belong on this list please advise) It's just a simple blog sort of thing that I'm trying to get my feet wet in web2py. Thank you again, zsb On Jun 15, 10:58 pm, mdipierro <[email protected]> wrote: > Because I think if you have a table1 that reference a table2 and a > table2 that reference table1 something is wrong. I am not even sure > all the database backends support that. think about it, you cannot > insert a record in table1 without the record in table2 to reference > and vice versa. The proper way to handle this is to have a table that > links table1 and table2. > > Anyway you can still do things like > > db.define_table('person', > Field('username', 'string'), > Field('image', 'integer'), # a forward reference to db.image > ) > > db.define_table('image', > Field('image', 'upload'), > Field('owner', db.person)) > > db.person.image.requires=IS_EMPTY_OR(IS_IN_DB(db,'image.id')) > db.person.image.represent=lambda id: > A('link',_href=URL(r=request,f='download',args=db.image[id].image)) > > On Jun 15, 10:24 pm, Yarko Tymciurak <[email protected]> > wrote: > > > > > On Jun 15, 1:56 pm, zsouthboy <[email protected]> wrote: > > > > Hi Yarko, > > > > Thanks for the help! > > > I had initially tried doing what the introductory docs show (which is > > > marking a reference like ("image", db.image) for a column), which > > > fails because there is no member 'image' of db yet. > > > Then I consulted the technical docs and saw that instead "reference > > > image" should be used instead, so tried that, thinking that it would > > > be used as a placeholder (and filled in correctly later). > > > When that failed, I posted here. > > > > The DAL doesn't recurse to allow this situation? Does anyone know > > > why / why not? When I get a chance I'll look at gluon and see how > > > trivial it would be to do, even in a hacky way. > > > ... consider dropping this from your vocabulary: ".... even in a hacky > > way..."; > > > > I do have a separate issue now: following what you've suggested, I now > > > get complaints from gluon that referenced tables have duplicate field > > > names as the table being defined - did I miss something obvious? That > > > seems like there should be no issue doing so. (you can get this error > > > Yes, it seems so: in gluon/(dal|sql).py, in > > Table._create_references(), there's: > > > if self._tablename in referee.fields: > > > with no comments - so beyond the shallow, immediate reading for that > > line, we have no clue > > as to the motivation / reasoning for this particular constraint > > (reverse engineering every little thing > > just to try to get what intended... besides being no better than > > guessing, mind-reading, > > also gets tedious). If you simply rename db.person.image to > > something w/o the 'image' (tablename), > > e.g. db.person.image_id --- this goes away. > > > As to forward references: > > I commented out the lines in Table._create_references() (and the > > exception it raises), and __get__ errors come, so there is at least > > that simple get/set work to do to get forward references; not sure if > > there would be anything else. Commented code _sure would be nice_! > > > - Yarko > > > > by simply copying and pasting the suggested fix you responded to me > > > with into a test db.py, even). Duplicate field names, but they're in > > > separate tables, so why the error? > > > > Traceback (most recent call last): > > > File "gluon/restricted.py", line 178, in restricted > > > exec ccode in environment > > > File "/var/www/web2py/applications/golb/models/db.py", line 93, in > > > <module> > > > Field('published', 'boolean')) > > > File "gluon/sql.py", line 1304, in define_table > > > t._create_references() > > > File "gluon/sql.py", line 1579, in _create_references > > > raise SyntaxError, 'Field: table %s has same name as a field in > > > referenced table %s' % (self._tablename, referee._tablename) > > > SyntaxError: Field: table image has same name as a field in referenced > > > table person
