python-tdd/src/apps/dashboard/forms.py

from django import forms
from django.core.exceptions import ValidationError
from .models import Item

DUPLICATE_ITEM_ERROR = "You've already logged this to your note"
EMPTY_ITEM_ERROR = "You can't have an empty note item"

class ItemForm(forms.Form):
    text = forms.CharField(
        error_messages = {"required": EMPTY_ITEM_ERROR},
        required=True,
    )

    def save(self, for_note):
        return Item.objects.create(
            note=for_note,
            text=self.cleaned_data["text"],
        )

class ExistingNoteItemForm(ItemForm):
    def __init__(self, for_note, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._for_note = for_note

    def clean_text(self):
        text = self.cleaned_data["text"]
        if self._for_note.item_set.filter(text=text).exists():
            raise forms.ValidationError(DUPLICATE_ITEM_ERROR)
        return text

    def save(self):
        return super().save(for_note=self._for_note)