On Sunday, July 10, 2016 at 4:38:33 PM UTC-4, [email protected] wrote:
>
> In my application a user enters a boolean value, and later the user can
> modify the value*.* I want to save the original value in another field,
> and the user shouldn't be able to see or alter the original value.
>
> Based on the stackoverflow
> <http://stackoverflow.com/questions/16280220/setting-the-default-of-a-database-field-to-the-value-of-another-field-in-web2py>
>
> conversation I tried a simple table with two methods
> db.define_table('mytable',
> Field('start_number', 'integer', requires=IS_NOT_EMPTY()),
> Field('n1', 'integer', default=request.post_vars.start_number),
>
n1 won't work because it is writable and therefore appears in the form,
which means even if you leave it blank, an empty string is submitted as its
value, which SQLFORM converts to a 0 (the default value is inserted only if
no value is submitted).
Here are two options:
db.define_table('mytable',
Field('modifiable_number', 'integer', requires=IS_NOT_EMPTY()),
Field('original1', 'integer', readable=False, writable=False,
default=request.post_vars.modifiable_number),
Field('original2', 'integer', readable=False, writable=False,
compute=lambda r: r.modifiable_number))
db.mytable._before_update = [lambda t, f: setattr(db.mytable.original2,
'compute', None)]
Because original1 is not writable, it will not appear in the form, which
means no value will be submitted for it and therefore its default value
will be inserted. Note, however, that this will not work in appadmin, which
ignores the "writable" attribute and will therefore include original1 in
the insert form.
original2 will use the computed value only on the initial insert. The
_before_update callback removes the "compute" attribute before any updates,
so no new value will be computed on updates. Note, if you need to do an
insert *after* an update during the *same* HTTP request (which is probably
not a common scenario), you would also need to add an _after_update
callback to restore the "compute" attribute after the update.
Anthony
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