django.db.utils.IntegrityError: UNIQUE constraint failed: rango_page__new.category_id

Question

i have trouble when i want to run this command

python manage.py migrate

and i get the error...i was trying to search how to fix it but i dont find how to fix, may be someone here can help me to fix this this is error waht i have gotten

Operations to perform:
  Apply all migrations: admin, rango, contenttypes, auth, sessions
Running migrations:
  Applying rango.0004_auto_20160107_0149...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/core/management/base.py", line 338, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/core/management/commands/migrate.py", line 161, in handle
    executor.migrate(targets, plan, fake=options.get("fake", False))
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/migrations/executor.py", line 68, in migrate
    self.apply_migration(migration, fake=fake)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/migrations/executor.py", line 102, in apply_migration
    migration.apply(project_state, schema_editor)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/migrations/migration.py", line 108, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/migrations/operations/fields.py", line 139, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/schema.py", line 470, in alter_field
    self._alter_field(model, old_field, new_field, old_type, new_type, old_db_params, new_db_params, strict)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/sqlite3/schema.py", line 202, in _alter_field
    self._remake_table(model, alter_fields=[(old_field, new_field)])
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/sqlite3/schema.py", line 146, in _remake_table
    self.quote_name(model._meta.db_table),
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/schema.py", line 111, in execute
    cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/utils.py", line 81, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/Django-1.7.11-py2.7.egg/django/db/backends/sqlite3/base.py", line 485, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: UNIQUE constraint failed: rango_page__new.category_id

and here my code

views.py

from django.shortcuts import render
from django.http import HttpResponse
from rango.models import Category, Page
from django.db.models import F
from rango.forms import CategoryForm, PageForm

# Create your views here.
def index(request):
#    return HttpResponse("Rango says: Hello world! <br /><a href='/rango/about/'>About</a>")
#    context_dict = {'boldmessage':'I am bold font from the contextx'}
#    return render(request, 'rango/index.html',context_dict)
    category_list = Category.objects.order_by('-likes')
    context_dict = {'categories':category_list}
    return render(request, 'rango/index.html', context_dict)

def about(request):
    return HttpResponse("Rango says here is the about page<br /><a href='/rango/'>Index</a>")

def category(request, category_name_slug):
    context_dict = {}

    try:
        category = Category.objects.get(slug=category_name_slug)
        context_dict['category_name'] = category.name

        pages = Page.objects.filter(category=category)

        context_dict['pages'] = pages
        context_dict['category'] = category
#        Category.objects.filter().update(views=F('views')+1)
    except Category.DoesNotExist:
        pass

    return render(request, 'rango/category.html', context_dict)

def add_category(request):
    if request.method == 'POST':
        form = CategoryForm(request.POST)

        if form.is_valid():
            form.save(commit=True)
            return index(request)
        else:
            print form.errors
    else:
        form = CategoryForm()

    return render(request, 'rango/add_category.html', {'form':form})

def add_page(request, category_name_slug):
    try:
        cat = Category.objects.get(slug=category_name_slug)
    except Category.DoesNotExist:
        cat = None

    if request.method == 'POST':
        form = PageForm(request.POST)
        if form.is_valid():
            if cat:
                page = form.save(commit=False)
                page.category = cat
                page.views = 0
                page.save()

                return category(request, category_name_slug)
        else:
            print form.errors
    else:
        form = PageForm()

    context_dict = {'form':form, 'category':cat, 'category_name_slug':category_name_slug}

    return render(request, 'rango/add_page.html', context_dict)

models.py

from django.db import models
from django.template.defaultfilters import slugify
# Create your models here.

class Category(models.Model):
    name = models.CharField(max_length=128, unique=True)
    views = models.IntegerField(default=0)
    likes = models.IntegerField(default=0)
    slug = models.SlugField(null=False)

    def save(self, *args, **kwargs):
        self.slug = slugify(self.name)
        super(Category, self).save(*args, **kwargs)

    def __unicode__(self):
        return self.name

class Page(models.Model):
    category = models.ForeignKey(Category)
    title = models.CharField(max_length=128)
    url = models.URLField(null=True)
    views = models.IntegerField(default=0, null=True)

#    def save(self, *args, **kwargs):
#        self.slug = slugify(self.name)
#        super(Category, self).save(*args, **kwargs)

    def __unicode__(self):      #For Python 2, use __str__ on Python 3
        return self.title

forms.py

from django import forms
from rango.models import Page, Category

class CategoryForm(forms.ModelForm):
    name = forms.CharField(max_length=128, help_text="Please enter the category name.")
    views = forms.IntegerField(widget=forms.HiddenInput(), initial=0)
    likes = forms.IntegerField(widget=forms.HiddenInput(), initial=0)
    slug = forms.CharField(widget=forms.HiddenInput(), required=False)

    # An inline class to provide additional information on the form.
    class Meta:
        # Provide an association between the ModelForm and a model
        model = Category
        fields = ('name',)


class PageForm(forms.ModelForm):
    title = forms.CharField(max_length=128, help_text="Please enter the title of the page.")
    url = forms.URLField(max_length=200, help_text="Please enter the URL of the page.")
    views = forms.IntegerField(widget=forms.HiddenInput(), initial=0, required=False )

    class Meta:
        # Provide an association between the ModelForm and a model
        model = Page

        # What fields do we want to include in our form?
        # This way we don't need every field in the model present.
        # Some fields may allow NULL values, so we may not want to include them...
        # Here, we are hiding the foreign key.
        # we can either exclude the category field from the form,
        exclude = ('category',)
        #or specify the fields to include (i.e. not include the category field)
        #fields = ('title', 'url', 'views')

what should i do to fix this !

Answer 1

okay its done, i just edit this script

rango/migrations/0004_auto_20160107_0149.py

old

class Migration(migrations.Migration):

    dependencies = [
        ('rango', '0003_category_slug'),
    ]

    operations = [
        migrations.AlterField(
            model_name='page',
            name='category',
            field=models.ForeignKey(to='rango.Category', unique=True),
            preserve_default=True,
        ),

to be

class Migration(migrations.Migration):

    dependencies = [
        ('rango', '0003_category_slug'),
    ]

    operations = [
        migrations.AlterField(
            model_name='page',
            name='category',
            field=models.ForeignKey(to='rango.Category', unique=False),
            preserve_default=True,
        ),

unique=True to be unique=False

okay done...