class ProblemsInContest(CreateUpdateDateModel):
    contest = models.ForeignKey(Contest)
    problem = models.ForeignKey(ContestProblem)

    class Meta:
        verbose_name = "Problem in Contest"
        verbose_name_plural = "Problems in Contest"

    def __str__(self):
        return "{problem}".format(problem=self.problem)

class ContestProblemInline(admin.TabularInline):
    model = ProblemsInContest
    extra = 1


class ContestAdmin(admin.ModelAdmin):

    inlines = [
        ContestProblemInline,
    ]

class ContestProblemInline(admin.TabularInline):

    model = ProblemsInContest

    def formfield_for_foreignkey(self, db_field, request=None, **kwargs):

        field = super(RoomInline, self).formfield_for_foreignkey(db_field, request, **kwargs)

        if db_field.name == 'your_field_name':
            if request._obj_ is not None:
                field.queryset = field.queryset.filter(your_field_name = request._obj_)
            else:
                field.queryset = field.queryset.none()

        return field



class ContestAdmin(admin.ModelAdmin):

    inlines = (ContestProblemInline,)

    def get_form(self, request, obj=None, **kwargs):
        # just save obj reference for future processing in Inline
        request._obj_ = obj
        return super(ContestAdmin, self).get_form(request, obj, **kwargs)