Personal Catalogue: Django & PostgreSQL — Chapter 2, Exercise 3
====================================================

TASK
Using the Django shell, create one book Item, create one Tag, attach
the tag to the book via item.tags.add(tag), then confirm the
relationship by printing item.tags.all().

SOLUTION

Open the Django shell:

    python manage.py shell

Then, inside the shell:

    >>> from catalogue.models import Item, ItemType, Tag
    >>> book_type = ItemType.objects.get(name='book')
    >>> item = Item.objects.create(
    ...     item_type=book_type,
    ...     title='FastAPI in Action',
    ...     creator='Bill Lubanovic',
    ...     release_year=2023,
    ... )
    >>> tag = Tag.objects.create(name='Python')
    >>> item.tags.add(tag)
    >>> item.tags.all()
    <QuerySet [<Tag: Python>]>

WHAT THIS ACTUALLY CONFIRMS

item.tags.add(tag) writes a real row into the automatically-generated
join table connecting this specific Item and this specific Tag - the
same underlying mechanism as manually inserting a row into a hand-built
item_tags table, just expressed through the ManyToManyField's own
Python API instead of raw SQL. item.tags.all() then queries that join
table (joined back to the Tag table) and returns every tag currently
attached to this item, confirming the relationship was actually
recorded rather than merely appearing to succeed.

A useful follow-up check: querying from the other direction,
tag.items.all() (using the related_name='items' set on the
ManyToManyField), should return a QuerySet containing the same book
Item - proving the relationship works symmetrically in both directions,
exactly as a real many-to-many relationship should.

WHY THIS WORKS AS AN ANSWER
----------------------------
It walks through the exact commands needed, explains what add() and
all() are actually doing at the database level rather than treating
them as opaque method calls, and suggests a real way to verify the
relationship is genuinely bidirectional.