Remove the selected option from the choice field in admin panel

Question

I want to reduce the choice option in the admin panel if it is selected once.

admin.py

class MyModelForm(forms.ModelForm):
    LOC = [('op1', 'op1'), ('op2', 'op2'),...]

    location = forms.ChoiceField(choices=LOC)


class DataModelAdmin(admin.ModelAdmin):
    form = MyModelForm
    list_display = ('location',)
    search_fields = ['location']

    def get_ordering(self, request):
        return ['location']


admin.site.register(DataModel, DataModelAdmin)

model.py

class DataModel(models.Model):
    location = models.CharField(max_length=50, unique=True)

    def __str__(self):
        return self.location

I am trying to do but it removes the selected option on restarting the server

Answer 1

If I'm interpreting your question correctly you want to remove the object's location from the field choices...

class MyModelForm(forms.ModelForm):
    LOC = [('op1', 'op1'), ('op2', 'op2')]

    location = forms.ChoiceField()

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        if self.instance:
            self.fields['location'].choices = [
                choice for choice in self.LOC
                if choice[0] != self.instance.location
            ]
        else:
            self.fields['location'].choices = self.LOC

Actually on second read maybe you're looking for a filter?

from django.contrib.admin import SimpleListFilter

class LocationFilter(SimpleListFilter):
    title = 'location'
    parameter_name = 'location'

    def lookups(self, request, model_admin):
        locations = DataModel.objects.values_list('location', flat=True)
        return locations

    def queryset(self, request, queryset):
        if self.value():
            return queryset.filter(location=self.value())

Then add list_filter = (LocationFilter,) to your admin class.