I am attempting to modify a page on my Django admin so that a trusted race
administrator can manually rearrange a leader board of race results. The
results go from 1 to N competitors in a race, and are mutually exclusive.
Draw results are not allowed, so race administrators apply often complex
and arcane tie breaking rules to avoid draws, which is the reason why they
require the facility to manually re-arrange results.
I have a model and validators here:
```
def number_of_ranks(value):
number_of_results = Rank.objects.all().count()
if value > number_of_results:
raise ValidationError(
_('%(value)s is bigger than number of results which is
%(number_of_results)s'),
params={'value': value, 'number_of_results': number_of_results},
)
class Rank(models.Model):
result = models.PositiveIntegerField(validators=[
MinValueValidator(1),
number_of_ranks]) # 1st, 2nd, 3rd = 1,2,3 etc - may be
assigned by administrator
team = models.ForeignKey( # team that achieved this
result
'team',
related_name='team_in_rank',
on_delete=models.PROTECT
)
```
and an admin page for Rank here:
```
@admin.register(Rank)
class RankAdmin(admin.ModelAdmin):
list_display = ('result', 'team',)
sortable_by = ('')
ordering = ('result',)
list_editable = ('result',)
list_display_links = None
def has_add_permission(self, request):
return False
def has_delete_permission(self, request):
return False
def save_model(self, request, obj, form, change):
print('-------------save_model called------------')
print(request)
print('================================')
print('All objects and results BEFORE change')
print([(rank, rank.result) for rank in Rank.objects.all()])
print('================================')
print('Changed object and changed result')
print(obj, obj.result)
print('================================')
super().save_model(request, obj, form, change)
print('All objects and results AFTER change')
print([(rank, rank.result) for rank in Rank.objects.all()])
```
This achieves some of what I want. That is
1. The admin can neither remove or add teams in the race, nor change the
names of any of the teams, only results.
2. Any result must be in the range 1 to N competitors.
3. The display of the teams is arranged in order of result. 1 on the top
row and N on the Nth row.
The over-ride of save_model() achieves nothing functional but is merely an
effort to discover something using print() calls about the validation and
save sequence. It seems to indicate to me that there is a separate and
individual call made to save_model() for each and every record that is
changed.
So that if I have four teams initially
1 Red, 2 Blue, 3 Yellow, 4 Green
and the admin wants to change this to
1 Blue, 2 Red, 3 Yellow, 4 Green
then that triggers two separate calls to save_model(): eg
1 Red, 2 Blue, 3 Yellow, 4 Green -> 1 Red, 1 Blue, 3 Yellow, 4 Green
and
1 Red, 1 Blue, 3 Yellow, 4 Green -> 1 Blue, 2 Red, 3 Yellow, 4 Green
(the actual stages can vary - the reds could change first)
What I want to be able to do is perform a final validation only after the
final record is changed so that I can check that every record has a unique
result in the range 1..N - i.e. there are no duplicated results. But in the
intermediate call(s) to save_model() there will inevitably be at least one
duplicated result - just one if the admin exchanges two results, but
potentially more if he attempts a more complicated reshuffle.
So I want to hook into / over-ride a procedure which is called just once
when triggered by pressing the Save button, after all the separate
save_model() calls are complete. I haven't been able to discover from the
docs how to do this, or even if it can be done. Possibly my approach to
this is wrong, either entirely or in part?
Any advice would be helpful.
Thanks
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