Deleting temporary elements in Many To Many list causes graphical and functional bug

[Riccardo-Maffei]

Maybe a duplicate of #212 , but I think there still are some differences, therefore I created this new issue. In order to reproduce the bug, a models.ManyToManyField with a through property has to be created. The Model referenced in the "through" should have an Inline class, setting all its fields to autocomplete mode.

Then the user has to create a few empty M2M fields in the admin site,

delete one or more in the middle of the list

and add a new one.

At this point the newly created element can still be deleted, but the autocomplete function won't work on this field anymore, making the input of new data in this field impossible.

Up until now I've found two manual fixes, either adding one field at a time or removing empty fields only if they are at the end of the list. These strategies could be a bit annoying however, especially for people that need to enter information quickly.

I will include pieces of my code in the comments, in case this isn't a bug and it was me who made a mistake.

[Riccardo-Maffei]

container_models.py :

from django.db import models
from django.forms import ModelForm

from .models.item_models import Item


class Container(models.Model):
    random_text = models.CharField(
        max_length=200,
        blank=False,
        null=False,
    )

    connections = models.ManyToManyField(
        Item,
        through='ContainerToItemConnector',
    )


class ContainerForm(ModelForm):
    class Meta:
        model = Container
        fields = '__all__'

item_models.py :

from django.db import models
from django.contrib import admin


class Item(models.Model):
    name = models.CharField(
        max_length=200,
        blank=False,
        null=False,
    )


class ItemAdmin(admin.ModelAdmin):
    search_fields = ['name']

container_to_item_connector_models.py :

import nested_admin

from django.db import models
from django.contrib import admin
from django.forms import ModelForm

from .models.item_models import Item
from .models.container_models import Container, ContainerForm


class Property(models.Model):
    class Meta:
        verbose_name_plural = 'Properties'

    name = models.CharField(
        max_length=200,
        blank=False,
        null=False,
    )


class PropertyAdmin(admin.ModelAdmin):
    search_fields = ['name']


class ContainerToItemConnector(models.Model):
    container = models.ForeignKey(
        Container,
        on_delete=models.CASCADE,
    )

    item = models.ForeignKey(
        Item,
        on_delete=models.CASCADE,
    )

    connections = models.ManyToManyField(
        Property,
    )


class ContainerToItemConnectorForm(ModelForm):
    class Meta:
        model = ContainerToItemConnector
        fields = '__all__'


class ContainerToItemConnectorAdmin(admin.ModelAdmin):
    form = ContainerToItemConnectorForm
    autocomplete_fields = ['item', 'connections']


class ContainerToItemConnectorInline(nested_admin.NestedTabularInline):
    model=ContainerToItemConnector
    form=ContainerToItemConnectorForm
    autocomplete_fields = ['item', 'connections']
    extra = 0


class ContainerAdmin(nested_admin.NestedModelAdmin):
    inlines=[ContainerToItemConnectorInline]
    form=ContainerForm