On Jul 4, 1:45 pm, Rick Hultgren <[email protected]> wrote: > ...with other words -- how to add fields to a table that is already > declared? Is it possible?
If they are tables which were created by web2py, then the db.table attribute is (by default) set for automatic migration - adding and deleting fields works (but: deleting a field _will_ generate an alter table SQL statement, so any data in those deleted fields will likely be lost). > > On 7/4/10, Rick Hultgren <[email protected]> wrote: > > > perhaps the table names will be changed, so please don't bother about > > "before" and "after"...the point is -- how to refer/link to the table > > name "locus", when that table is not yet created/declared/made? > > > On 7/4/10, Rick Hultgren <[email protected]> wrote: > >> Thanks for the answers. I'm trying to create these tables: > I would (again) suggest you draw the relationships - to simplify this, notice you do not need double-linked references (hardly ever) - leave this for a later stage of development (it is something you can do to try to improve performance). If you want to know all the components that refer to record (id) # 7 of db.substance, then you would (for example) search thus: db.( db.process.substance_id == db.substance.id).select(ALL) Also, I will re-introduce what I think will help you think about this - call all reference fields in a way that emphasizes that they are references, by referred table id. Since you still haven't diagrammed out the relationship (two-way links can mask the true relationship needed) - I will guess at parent/child (or responsible / dependent) relations; if I get them wrong, then you will know for your application how to invert them. I'll assume hierarchy suggested by the order of table definitions you have given. > >> db.define_table( 'substance', > >> Field( 'substance', db.substance), > >> Field( 'process', db.process), > >> Field( 'condition', db.condition), > >> Field( 'locus', db.locus), > >> Field( 'name'), > >> Field( 'main_name')) db.define_table('substance', Field('name'), Field('main_name')) # all that's needed for this; > > >> db.define_table( 'process', > >> Field( 'substance', db.substance), > >> Field( 'process', db.process), > >> Field( 'condition', db.condition), > >> Field( 'locus', db.locus), > >> Field( 'name'), > >> Field( 'main_name')) db.define_table('process', Field('name'), Field('main_name'), # now only add references to tables "above": Field('substance_id', db.substance)) # a process related to a substance?? > > >> db.define_table( 'condition', > >> Field( 'substance', db.substance), > >> Field( 'process', db.process), > >> Field( 'condition', db.condition), > >> Field( 'locus', db.locus), > >> Field( 'name'), > >> Field( 'main_name')) # assuming that the condition cannot be cross-lined to one process, but a different substance; need clear model to show what is really needed db.define_table('condition', Field('name'), Field('main_name'), Field('process_id', db.process)) > > >> db.define_table( 'locus', > >> Field( 'substance', db.substance), > >> Field( 'process', db.process), > >> Field( 'condition', db.condition), > >> Field( 'locus', db.locus), > >> Field( 'name'), > >> Field( 'main_name')) # this could be related to either process or condition..... I'll just assume process for now db.define_table('locus', Field('name'), Field('main_name'), Field('process_id', db.process)) This is the kind of relationships I would expect you might start with (and something that would give you all the information you needed;) Perhaps this is helpful. Regards, - Yarko > > >> On 7/4/10, mdipierro <[email protected]> wrote: > >>> Could you explain to us in English what you are trying to model? I am > >>> sure there is a simpler solution using link tables. > > >>> On 3 Lug, 12:14, Rick Hultgren <[email protected]> wrote: > >>>> Thanks for the link. My actual problem is more complicated than the > >>>> example I gave. I realize that I need to link a field to a table that > >>>> isn't initiated yet (item2): > > >>>> objects = ['substance', 'process', 'condition', 'locus'] > >>>> linksubobjects = ['locus', 'before', 'after'] > >>>> unlinksubobjects = ['name', 'main_name'] > >>>> for object in objects: > >>>> for item1 in linksubobjects+unlinksubobjects: > >>>> for item2 in objects: > >>>> fields=[Field(item1, 'reference > >>>> item2')] > >>>> db.define_table(object,*fields) > > >>>> I suppose the solution would be to initiate the table names and then > >>>> add the fields either in db.py, or in the controller file. But I have > >>>> no idea how to do this. > > >>>> On 7/3/10, Yarko Tymciurak <[email protected]> wrote: > > >>>> > The online book has a fairly useful search; > > >>>> > For your question, see: > >>>> >http://web2py.com/book/default/section/6/13 > > >>>> > Regards, > >>>> > - Yarko > > >>>> > On Jul 3, 8:45 am, Rick <[email protected]> wrote: > >>>> >> Hi, > > >>>> >> I would like to link a table to its own model like this: > > >>>> >> db.define_table('person', > >>>> >> Field('name'), > >>>> >> Field('child', db.person)) > > >>>> >> I understand that I should first initiate the table and then link it > >>>> >> to itself. But how to do that? > > >>>> >> Thanks in advance for help!
