Re: need help - following django tutorial to create polls database - missing "on delete cascade" - using django 2.2.1 with mysql 8.0

The notes say:

• The exact output will vary depending on the database you are using. The example above is generated for PostgreSQL.

Are you using the default SQLite?

You could try running migrate and then checking the tables to see if the constraint was added using a DB admin viewer.

For SQLite I use - https://sqlitebrowser.org/

For Postgres  - https://www.pgadmin.org/

On Tuesday, May 28, 2019 at 7:44:44 PM UTC-5, K Tan wrote:

Hi, everyone,

This is my first time using Django and I think I'm missing something or there is a bug. I am following the instructions on (https://docs.djangoproject.com/en/2.2/intro/tutorial02/) and I've just added the following chunk of code to "polls/models.py". (I copied/pasted so I know it's correct.)

<quote>

from django.db import models


class Question(models.Model):
    question_text = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')


class Choice(models.Model):
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)

</quote>

Then I ran the following command:

<quote>

LITTLEBLACK:www samktan$ python3 manage.py makemigrations polls
Migrations for 'polls':
  polls/migrations/0001_initial.py
    - Create model Question
    - Create model Choice

</quote>

Which is missing one line compared to the tutorial:

    - Add field question to choice

Now when I run this command:

<quote>

LITTLEBLACK:www samktan$ python3 manage.py sqlmigrate polls 0001

BEGIN;
--
-- Create model Question
--
CREATE TABLE `polls_question` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `question_text` varchar(200) NOT NULL, `pub_date` datetime(6) NOT NULL);
--
-- Create model Choice
--
CREATE TABLE `polls_choice` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `choice_text` varchar(200) NOT NULL, `votes` integer NOT NULL, `question_id` integer NOT NULL);
ALTER TABLE `polls_choice` ADD CONSTRAINT `polls_choice_question_id_c5b4b260_fk_polls_question_id` FOREIGN KEY (`question_id`) REFERENCES `polls_question` (`id`);
COMMIT;

</quote>

It is missing the "on delete cascade" clause, which I suspect it caused by the missing line above.

I have confirmed in MySQL that the "on delete cascade" clause is definitely missing.

<quote>

mysql> show create table `polls_choice`;
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table        | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| polls_choice | CREATE TABLE `polls_choice` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `choice_text` varchar(200) COLLATE utf8mb4_general_ci NOT NULL,
  `votes` int(11) NOT NULL,
  `question_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `polls_choice_question_id_c5b4b260_fk_polls_question_id` (`question_id`),
  CONSTRAINT `polls_choice_question_id_c5b4b260_fk_polls_question_id` FOREIGN KEY (`question_id`) REFERENCES `polls_question` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci |
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

</quote>

Can someone tell me what I'm doing wrong?

--

/ per ardua ad astra /

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