Now I understand. There is not api exposed to do this but you can with
a trick
if 'ADD fieldname' in db._lastsql:
do_whatever_you_need_to_do()
On Oct 6, 8:48 am, Scott Hunter <[email protected]> wrote:
> My scenario is that I have version X of an appliance which is missing
> the field in question, and I add it to the model for version X+1.
> Currently, web2py will handle adding that field to the appropriate
> table when the new version of the appliance is run for the first time
> using the new model. So while I know when it is added to the model, I
> don't know when it is added to the DB without performing a query. I
> suppose I could add a statement to update this field whereever it is
> NULL, but I don't really want to execute this every time the model
> gets evaluated. If I knew when the field was actually added to the
> DB, then I could do this initialization at just that point.
>
> Similarly for adding a table: if I knew when the table in the DB
> actually gets created, then I could add my initial record at that
> point, and not do a query to see if this is necessary every time the
> model gets evaluated.
>
> - Scott
>
> On Oct 6, 9:36 am, mdipierro <[email protected]> wrote:
>
> > Perhaps I do not understand the question. If you add a field you know
> > you are adding it. If you need to initialize it with a function then
> > you have to loop over all records and to an update_record. Are you
> > trying to prevent the update from accidentally happening twice?
>
> > Massimo
>
> > On Oct 5, 6:26 pm, Scott Hunter <[email protected]> wrote:
>
> > > Thanks for the quick reply!
>
> > > The situation I'm interested in is where the field doesn't exist and
> > > I'm adding it as a UNIQUE field; v1.65.10 generates a ticket when the
> > > appliance starts up, saying it can't add a UNIQUE field, which seems
> > > odd, since field creation is pretty much the only time you're assured
> > > there would be no conflict.
>
> > > I may be mistaken about being able to add UNIQUE=true once the field
> > > already exists. I'll check out the latest version, and see if that
> > > addresses the issue.
>
> > > Any ideas about the initialization questions?
>
> > > - Scott
>
> > > On Oct 5, 5:45 pm, mdipierro <[email protected]> wrote:
>
> > > > I believe something has changed about this since 1.65.10 so you may
> > > > want to look at a more recent version (1.86.2 has lots of bug fixes).
> > > > I do not remember exactly the details about what changed in this
> > > > respect. In general the problem is that if you make a field unique,
> > > > after there is data in it, web2py has no way of knowing if the data
> > > > already in was unique or not and there is no easy way of checking.
>
> > > > On Oct 5, 4:13 pm, Scott Hunter <[email protected]> wrote:
>
> > > > > 1) I want to let migration add a UNIQUE=true field to a table, which
> > > > > apparently isn't allowed. But what does seem to be allowed is having
> > > > > the field added w/ UNIQUE=false, and after restarting the server (now
> > > > > that the field exists), having UNIQUE=true. Is there a way to
> > > > > accomplish this w/ the restart?
>
> > > > > 2) Related to the above, is it possible to detect when this field will
> > > > > be added, so that I can initialize it? Unfortunately, it has to be
> > > > > computed, so unless default can be a function that gets called (it
> > > > > wouldn't need any arguments), I don't see how this could be done.
>
> > > > > 3) s there a way to tell when a define_table has to actually create
> > > > > the table, so I can stuff in an initial record? I suppose I could do
> > > > > a query after the definition, but then it will get done for every
> > > > > request.
>
> > > > > Thanks in advance,
> > > > > Scott Hunter
>
> > > > > P.S. I'm currently using v1.65.10; if a newer version would help
> > > > > address any of these, that'd bolster my argument to upgrade!
>
>
