NOT NULL 约束失败：

Question

I am creating a website where people under the topics set by the administrator will be able to make their entries. Each record is linked to a user account, but when creating a new record, an error appears - NOT NULL constraint failed: menu_description.topic_id

menu/views.py

from django.shortcuts import render, redirect
from .models import Topic, Description
from .forms import DescriptionForm
from django.contrib.auth.decorators import login_required



def index(request):
    topic = Topic.objects.all
    context = {'topic': topic}
    return render(request, 'Menu/Menu.html', context)


@login_required
def description(request, topic_id):
    topic = Topic.objects.get(id=topic_id)
    description = topic.description_set.filter(owner=request.user).order_by('date_added')
    context = {'description': description, 'topic': topic}
    return render(request, 'Menu/Description.html', context)


@login_required
def new_description(request, topic_id):
    topic = Topic.objects.get(id=topic_id)
    if request.method != 'POST':
        form = DescriptionForm()
    else:
        form = DescriptionForm(data=request.POST)
        if form.is_valid():
            new_description = form.save(commit=False)
            new_description.owner = request.user
            new_description.save()
            return redirect('description', topic_id=topic_id)
    context = {'topic': topic, 'form': form}
    return render(request, 'Menu/new_description.html', context)


@login_required
def edit_description(request, entry_id):
    description = Description.objects.get(id=entry_id)
    topic = description.topic
    if request.method != 'POST':
        form = DescriptionForm(instance=description)
    else:
        form = DescriptionForm(instance=description, data=request.POST)
        if form.is_valid():
            form.save()
            return redirect('description', topic_id=topic.id)
    context = {'description': description, 'topic': topic, 'form': form}
    return render(request, 'Menu/Edit_description.html', context)


@login_required
def delete_description(request, description_id):
    description = Description.objects.get(id=description_id)
    topic = description.topic
    description.delete()
    return redirect('description', topic_id=topic.id)

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menu/models.py

from django.db import models
from django.contrib.auth.models import User


class Topic(models.Model):
    text = models.CharField(max_length=100)

    def __str__(self):
        return self.text


class Description(models.Model):
    topic = models.ForeignKey(Topic, on_delete=models.CASCADE)
    text = models.TextField()
    date_added = models.DateTimeField(auto_now_add=True)
    owner = models.ForeignKey(User, on_delete=models.CASCADE)

    class Meta:
        verbose_name_plural = 'Descriptions'

    def __str__(self):
        if len(self.text) > 100:
            return f'{self.text[:100]}...'
        else:
            return self.text

Answer 1

The reason you are getting this error is that you are not associating any topic to the newly created Description . Let's give it a try

        # ...
        form = DescriptionForm(data=request.POST)
        if form.is_valid():
            new_description = form.save(commit=False)
            new_description.owner = request.user
            new_description.topic = topic  # new
            new_description.save()
            # ....

Answer 2

In your code, please set new_description.topic , in def edit_description , so:

@login_required
def new_description(request, topic_id):
    topic = Topic.objects.get(id=topic_id)
    if request.method != 'POST':
        form = DescriptionForm()
    else:
        form = DescriptionForm(data=request.POST)
        if form.is_valid():

            # >>>> SET TOPIC HERE <<<<<<<
            new_description.topic = topic

            new_description = form.save(commit=False)
            new_description.topic = topic
            new_description.owner = request.user
            new_description.save()

            return redirect('description', topic_id=topic_id)
    context = {'topic': topic, 'form': form}
    return render(request, 'Menu/new_description.html', context)