[PYTHON] Django starting from scratch (part: 2)

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Django starting from zero \ (part: 1 ) -Qiita

References

Creating your first Django app, part 2|Django documentation| Django

DataBase settings

mysite/setting.py --Python module that describes various settings of jango --Database support etc. are included by default

INSTALLED_APPS Settings for important parts of the application. Details below --django.contrib.admin --Administration (admin) site --django.contrib.auth --Authentication system --django.contrib.contenttypes --Contenttypes framework --django.contrib.sessions --Session framework --django.contrib.messages --Message framework --django.contrib.staticfiles --Static file management framework

Creating a table

Use the following command to create a database table.

python manage.py migrate

-The migrate command refers to the INSTALLED_APPS settings above and creates all the required databases according to the database settings in the` mysite / setting.py' file. --It is possible to display the contents of the table with the command line client. - \dt (PostgreSQL - SHOW TABLES; (MySQL) - .schema (SQLite) - SELECT TABLE_NAME FROM USER_TABLES; (Oracle)

Generate database model

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)

--Generating two models, Question and Choice --Both are subclasses of the models class --Each class represents the database feel of the model

--CharFiled, IntegerField, etc. specify what data type to store --Conditions and initial values can be specified, such as models.CharField (max_length = 200) and models.IntegerField (default = 0) --Foreign Key defines a relationship with Question.

Reflect the application in the project

--Add the setting to ʻINSTALLED_APPS in setting.py' to include the application in your project --Set the class described in ʻapps.py in the application (this time Polls) to ʻINSTALLED_APPS

INSTALLED_APPS = [
    'polls.apps.PollsConfig',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

Reflect model changes

Run the code below to save Django's changes in the form of a migration

python manage.py makemigrations polls

• Migration: How Django saves model (database schema) changes.

 python manage.py check 

Command to check if there is a problem with the project

After creating the model table, execute migrate again to create the model table in the database.

3 steps to implement model changes

--Change model --Run python manage.py make migrations to create migrations --Run python manage.py migrate to apply these changes to the database

Why are the commands for creating and applying migrations separate?

--To commit the migration to the validation management system and distribute it with the app --Easy development ――Because it will be easy to use for other developers and production environments

Improved convenience of database API

If you do >>> Question.objects.all () in the shell The output is as follows. <QuerySet [<Question: Question object (1)>]> I don't know what the database tables look like

So add the `str'method to both Question and Choice

from django.db import models

class Question(models.Model):
    # ...
    def __str__(self):
        return self.question_text

class Choice(models.Model):
    # ...
    def __str__(self):
        return self.choice_text

--In addition to the convenience of displaying in the shell, it is used as an object representation of django's auto-generated admin object. --So it's important to add the __str __ () method to your model

polls/models.py

from django.db import models
from django.utils import timezone


class Question(models.Model):
    # ...
    def was_published_recently(self):
        return self.pub_date >= timezone.now() - datetime.timedelta(days=1)

Create an admin user

python manage.py createsuperuser

Make it editable on admin

from django.contrib import admin

from .models import Question

admin.site.register(Question)