django - inline - Search for existing record instead of adding a new one

Question

I have a library with shelves and books. I point each book to one shelf in a one-to-many relationship. If a book is pointing to a Null it means that it's in the library, but not in the shelf yet.

#models.py

class Shelf(models.Model):
    pass

class Book(models.Model):
    shelf = models.ForeignKey(Shelf, blank=True, null=True)

Then:

#admin.py

class BookInLine(admin.TabularInLine):
    model = Book
    extra = 0

class Shelf(admin.ModelAdmin):
    inlines = [ BookInLine, ]

When I edit the Shelf I can see and modify all the books that are in that shelf.

Problem:

• I have a lot of books already in the library (pointing to Null).
• If I click 'Add another Book' from the inline it will create a totally new book. But I want to avoid that. I would like to select from the books that are already in the library but doesn't belong to any shelf yet.

Answer 1

Hi the following code worked for me:

from widgets import ImproveRawIdFieldsForm

class BookInline(admin.TabularInline):
    model = Book
    raw_id_fields=('shelf',)
    extra =1
class Shelf(ImproveRawIdFieldsForm):
    inlines = [BookInline,]

It creates an admin view where you will se the normal Shelf stuff and the additional inline which is a raw id field and you have the posssibility to add new relations and you can chose from existing objects with the "magnifier" icon, which results in a pop-up of a list of all existing books. Besides chose one Book in the pop-up you can also create new Books there. So from my understanding this solves all your requirements

a better solution for this problem is explained here: one-to-many inline select with django admin

edited for your use-case:

#models.py
class Book(models.Model):
    shelf = models.ForeignKey(Shelf, blank=True, null=True, related_name="in_shelf")

#admin.py
class ShelfForm(forms.ModelForm):
    class Meta:
        model = Shelf

    books = forms.ModelMultipleChoiceField(queryset=Book.objects.all())

    def __init__(self, *args, **kwargs):
        super(ShelfForm, self).__init__(*args, **kwargs)
        if self.instance:
            if self.instance.in_shelf:
                self.fields['books'].initial = self.instance.in_shelf.all()
            else:
                self.fields['books'].initial = []

    def save(self, *args, **kwargs):    
        instance = super(ShelfForm, self).save(commit=False)
        self.fields['books'].initial.update(shelf=None)
        self.cleaned_data['books'].update(shelf=instance)
        return instance