Question

In the admin I want to use inline elements. I want category to display
the items it is related to.

But I get this error:

Exception at /admin/store/category/7/
<class 'store.models.Item'> has no ForeignKey to
<class 'store.models.Category'>

It’s true, of-course, since I chose to use Category to point to the
items it has.
But, how can I get the admin to list in-line all the items that a
given Category has?
How can I get around this error?

CONTEXT:

class Category:
    items=models.ManyToManyField(Item,through='Categoryhasitem')'

class Categoryhasitem(models.Model):
    category = models.ForeignKey(Category, db_column='category')
    item = models.ForeignKey(Item, db_column='item')

class Item(models.Model):
    id = models.AutoField(primary_key=True)

This is my admin.py file.

class ItemInline(admin.TabularInline):
    model=Item
class CategoryAdmin(admin.ModelAdmin):
    inlines=[ItemInline,]
class ItemAdmin(admin.ModelAdmin):
    pass
admin.site.register(Category, CategoryAdmin)
admin.site.register(Item, ItemAdmin) 

Answer 1

The syntax is slightly different to display many-to-many relations using an inline.

class ItemInline(admin.TabularInline):
    model = Category.items.through

class CategoryAdmin(admin.ModelAdmin):
    inlines = [
        ItemInline,
    ]
    exclude = ('items',)

See the django admin docs for working with many-to-many models for more details.