id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
7444	Provide API method for appending errors	Daniel Pope <dan@…>	nobody	"On occasion form errors only come to light after a form has been validated. There should be an method to add errors to a form after validation is complete.

A common scenario is for unique database fields. If you test whether the value is unique when cleaning, you introduce a race condition, because the value won't be saved until later. The safe method is this:

{{{
if form.is_valid():
    try:
        form.save()
    except IntegrityError:
        form._errors['my_unique_field'] = form.error_class([u""This value already exists. Please choose again""])
    else:
        ...
}}}

This works well, but this is an implementation-specific, undocumented method. I'd propose something like

{{{
form['my_unique_field'].add_error(u""This value must be unique"")
}}}

for field-specific errors and

{{{
form.add_error(u""This combination of foo and bar already exists"")
}}}

for non-field errors. These would either raise an error if validation had not yet occurred, or attempt validation before appending the error."	New feature	closed	Forms	dev	Normal	duplicate		bronger@…	Design decision needed	0	0	0	0	0	0