Django Quick Start-Database models

# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
INSTALLED_APPS = [
　　　　'polls.apps.PollsConfig',
　　　　'django.contrib.admin',
　　　　'django.contrib.auth',
　　　　'django.contrib.contenttypes',
　　　　'django.contrib.sessions',
　　　　'django.contrib.messages',
　　　　'django.contrib.staticfiles',
]

# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
C:\Python27\mysite>python manage.py makemigrations polls
　Migrations for 'polls':
　　　0001_initial.py:
　　　　　-　Create model Choice
　　　　　-　Create model Question
　　　　　-　Add field question to choice
　C:\Python27\mysite>

By running makemigrations, you tell Django that you have made some changes to the model (in this case, it is already up to date), and you want to store these changes as a migration.

Migrations are how Django stores your changes to the model (determined by your database schema)- They are just files on the disk. If you like, you can read the new model migration, it is in the file 'polls':/migrations/0001_initial.py. You wouldn't want Django to read them every time, but they are designed to be editable by humans, so you know how Django changes and can manually adjust them.

There is also a command to run migrations, which automatically manages the database schema (tables):　-　This is what is called a migration, let's see how SQL knows to run the migration. The 'sqlmigrate' command returns the migration name to the SQL display:

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
$ python manage.py sqlmigrate polls 0001

You should see something similar to the following (we have reformatted it for readability):

# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
C:\Python27\mysite>python manage.py sqlmigrate polls 0001
　BEGIN;
　--
　--　Create model Choice
　--
　CREATE TABLE "polls_choice" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "c
　hoice_text" varchar(200) NOT NULL, "votes" integer NOT NULL);
　--
　--　Create model Question
　--
　CREATE TABLE "polls_question" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
　"question_text" varchar(200) NOT NULL, "pub_date" datetime NOT NULL);
　--
　--　Add field question to choice
　--
　ALTER TABLE "polls_choice" RENAME TO "polls_choice__old";
　CREATE TABLE "polls_choice" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "c
　hoice_text" varchar(200) NOT NULL, "votes" integer NOT NULL, "question_id" integer
　er NOT NULL REFERENCES "polls_question" ("id"));
　INSERT INTO "polls_choice" ("choice_text", "votes", "id", "question_id") SELECT
　"choice_text", "votes", "id", NULL FROM "polls_choice__old";
　DROP TABLE "polls_choice__old";
　CREATE INDEX "polls_choice_7aa0f6ee" ON "polls_choice" ("question_id");
　COMMIT;
　C:\Python27\mysite>

The migration command will run all migrations that have not yet been applied (Django tracks which ones are applied in a special table named django_migrations in the database) in the database　-　Basically, it will use the model to synchronize changes in the database schema.

Using the API

Now, let's enter the interactive Python shell and the API provided by Django. To call the Python command line, please use the following command:

# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
C:\Python27C:\Python
　\mysite>python manage.py shell　2Python7Python10　.　23　2015(default, May9:44:00) [MSC v., 01500　64　bit (AMD64) on wi
　n32
　Type "help", "copyright", "credits" or "license" for more information.
　(InteractiveConsole)
　>>>

Just type "python" instead, because manage.py sets the DJANGO_SETTINGS_MODULE environment variable, which gives Django Python import paths to mysite/settings.py file.

# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
>>> import django
　>>> django.setup()

# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
>>> from polls.models import Question, Choice # import the model classes we just wrote.
　# No questions are in the system yet.
　>>> Question.objects.all()
　[]
　# Create a new Question.
　# Support for time zones is enabled in the default settings file, so
　# Django expects a datetime with tzinfo for pub_date. Use timezone.now().
　# instead of datetime.datetime.now() and it will do the right thing.
　>>> from django.utils import timezone
　>>> q = Question(question_text="What's new?", pub_date=timezone.now())
　# Save the object into the database. You have to call save() explicitly.
　>>> q.save()
　# Now it has an ID. Note that this might say "1instead of "1depending
　# on which database you're using. That's no biggie; it just means your
　# The database backend prefers to return integers as Python long integer
　# objects.
　>>> q.id
　1
　# Access model field values via Python attributes.
　>>> q.question_text
　"What's new?"
　>>> q.pub_date
　datetime.datetime(2012,　2,　26,　13, 0, 0,　775217, tzinfo=<UTC>)
　# Change values by changing the attributes, then calling save().
　>>> q.question_text = "What's up?"
　>>> q.save()
　# objects.all() displays all the questions in the database.
　>>> Question.objects.all()
　[<Question: Question object>]

Here we need to wait a while. The '<Question: Question object>' is a useless representation of this object. Let's solve this problem: by editing the Question model (in the polls/Add a '__str__' method to these Question and Choice models in the models.py file):

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
import datetime
　from django.utils.encoding import python_2_unicode_compatible
　@python_2_unicode_compatible # only if you need to support Python　2
　from django.utils import timezone
　　　　　class Question(models.Model):
　　　　　def __str__(self):
　　　　　　　　　return self.question_text
　@python_2_unicode_compatible # only if you need to support Python　2
　class Choice(models.Model):
　　　　　class Question(models.Model):
　　　　　def __str__(self):
　　　　　　　　　return self.choice_text

It is very important to add the '__str__' method, using interactive prompts to handle adding to the model, which is not only convenient for yourself but also because the object representation is used for the entire Django to automatically generate management.

注意，这些都是正常的Python方法。让我们添加一个自定义的方法，这里只是为了演示：polls/Note that these are all normal Python methods. Let's add a custom method here just for demonstration: polls

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
models.py
　import datetime
　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()1)

Note that here we add import datetime and from django.utils import timezone, referencing Python's standard datetime module and Django's time zone-related utilities in django.utils.timezone. If you are not familiar with time zone handling in Python, you can read 　Time zone support documentation.

Save these changes and run python manage.py shell again to start a new Python interactive shell:

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
>>> from polls.models import Question, Choice
　# Make sure our __str__() addition worked.
　>>> Question.objects.all()
　[<Question: What's up?>]
　# Django provides a rich database lookup API that's entirely driven by
　# keyword arguments.
　>>> Question.objects.filter(id=1)
　[<Question: What's up?>]
　>>> Question.objects.filter(question_text__startswith='What')
　[<Question: What's up?>]
　# Get the question that was published this year.
　>>> from django.utils import timezone
　>>> current_year = timezone.now().year
　>>> Question.objects.get(pub_date__year=current_year)
　<Question: 怎么了？>
　# 请求一个不存在的ID，这将引发异常。
　>>> Question.objects.get(id=2)
　Traceback (most recent call last):
　　　　　...
　DoesNotExist: 没有匹配查询的问题。
　# 通过主键查找是最常见的用例，因此Django提供
　# primary的快捷方式-key exact lookups.
　# 以下与Question.objects.get(id=)相同1).
　>>> Question.objects.get(pk=1)
　<Question: 怎么了？>
　# 确保我们的自定义方法工作。
　>>> q = Question.objects.get(pk=1)
　>>> q.was_published_recently()
　True
　# 给问题添加几个选择。create调用构建一个新的
　# Choice对象，执行INSERT语句，将选择添加到集合中
　# 可用选择数并返回新的Choice对象。Django创建
　# 用于存储外键关系的“另一侧”的集合
　# （例如，一个问题选择）可以通过API访问。
　>>> q = Question.objects.get(pk=1)
　# 显示相关对象集中任何选择　--　目前还没有。
　>>> q.choice_set.all()
　[]
　# 创建三个选项。
　>>> q.choice_set.create(choice_text='不多', votes=0)
　<Choice: 不多>
　>>> q.choice_set.create(choice_text='天空', votes=0)
　<Choice: 天空>
　>>> c = q.choice_set.create(choice_text='再次破解', votes=0)
　# Choice对象可以通过API访问其相关的Question对象。
　>>> c.question
　<Question: 怎么了？>
　# 反之亦然：Question对象可以访问Choice对象。
　>>> q.choice_set.all()
　[<Choice: 不多>, <Choice: 天空>, <Choice: 再次破解>]
　>>> q.choice_set.count()
　3
　# API会自动跟随所需的关系。
　# 使用双下划线来分隔关系。
　# 可以嵌套到任意深度；没有限制。
　# 查找所有pub_date在本年的任何问题的Choices。
　# (重新使用上面创建的'current_year'变量).
　>>> Choice.objects.filter(question__pub_date__year=current_year)
　[<Choice: 不多>, <Choice: 天空>, <Choice: 再次破解>]
　# 删除其中一个选项。使用delete()函数。
　>>> c = q.choice_set.filter(choice_text__startswith='Just hacking')
　>>> c.delete()

Introduction to Django management

Create an admin user

First, we need to create a user who can log in to the management interface. Run the following command:

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08c:\python27\mysite> python manage.py createsuperuser

Enter the username you want (any one), then press Enter.

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
Username: admin

Then, you will be prompted to enter an email address (any one):

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
Email address: [email protected]

The final step is to enter the password. It will ask for the password twice, the second time for confirmation.

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
Password:　**********
　Password (again):　*********
　Superuser created successfully.

Start the development server

The Django management site is activated by default. Let's start the development server and explore it.

If the server is not running, start it as follows:

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
c:\python27\mysite>python manage.py runserver

Now, open a web browser and enter "/admin/"Local domain"-　For example,　 　http://127.0.0.1:8000/admin/　　You should see the admin login interface: 　

Since it is enabled by default, the login screen may display in your own language, and since translation is enabled by default, the login screen may display in your own language,

Enter the admin website

Now, try to log in with the superuser account created in the previous step. You should see the Django management home page: 　

You should see some editable content: groups and users. They are provided by django.contrib.auth, Django's authentication framework.

Modify the poll management program

application where is the poll? It will not be displayed on the management index page.

There is only one thing to do: we need to tell the admin that the Question object has a management interface. To do this, open the polls/Modify the admin.py file as follows: 　

　# Filename : example.py
# Copyright :　2020 By w3codebox
# Author by: www.oldtoolbag.com
# Date :　2020-08-08
from django.contrib import admin
　from models import Question
　admin.site.register(Question)

Explore management features

Now that we have registered Question, Django knows it should be displayed on the main management page:

Click 'Questions'. Now, view the questions on the 'change list' page. This page displays all questions in the database and allows you to select one to change. There is also the question we created earlier:

Click on the 'What's new?' question to edit:

Items to note are listed here:

Modify 'Date published' by clicking the 'Today' and 'Now' shortcuts. Then click 'Save and continue editing.' and then click 'History' in the upper right corner. You will see a page listing all changes made to this object through Django management, with the username of the modifier and timestamp: 　 Code Download: 　http://pan.baidu.com/s/1jGR3wDg