Mac Docker 建立第一個Django 應用，Part 2

第二步：Mac Docker建立第一個Django 應用，Part 2

原文：Writing your first Django app, part 2
本文Python搭建在 Django Compose + Djang 執行Python需進入web server容器中，請參看[第一步：在Mac構建Django 容器]
翻譯整理：CK

Part 2：配置後端

1. 配置數據庫

已有建有的項目爲mysite，Docker Django 的教程裏創建了一個composeexample，這裏不適用它。假設咱們的真實項目爲mysite，打開myiste/settings.py，默認配置的數據庫是SQLite，SQLite包含在Python裏，無需安裝任何其餘東西。若是第一次建立真實的項目，仍然但願用可伸縮性更強的數據庫像PostgreSQL，省得未來又要切換數據庫則：

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'postgres',
        'USER': 'postgres',
        'HOST': 'db',
        'PORT': 5432,
    }
}

其餘數據庫綁定參考：Database Bindings

因爲使用了Docker容器來運行python，數據遷移$ python manage.py migrate也須要在容器裏作，因此先查看容器

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
bf1ef3b74f1b        mysite_web          "python3 manage.py..."   About an hour ago   Up 13 minutes       0.0.0.0:8000->8000/tcp   mysite_web_1
09f6cebc8741        postgres            "docker-entrypoint..."   2 hours ago         Up 13 minutes       5432/tcp                 mysite_db_1

進入容器並執行migrate：

docker exec -it mysite_db_1 bash
$ python manage.py migrate

這條命令根據myiste/settings.py裏的 INSTALLED_APPS 的須要安裝必要數據庫表格，安裝完成後再鏈接PostgreSQL psql DBNAME USERNAME

root@09f6cebc8741:/# psql postgres postgres

輸入\dt 應該能看到相似Tables

postgres=# \dt
                   List of relations
 Schema |            Name            | Type  |  Owner
--------+----------------------------+-------+----------
 public | auth_group                 | table | postgres
 public | auth_group_permissions     | table | postgres
 public | auth_permission            | table | postgres
 public | auth_user                  | table | postgres
 public | auth_user_groups           | table | postgres
 public | auth_user_user_permissions | table | postgres
 public | django_admin_log           | table | postgres
 public | django_content_type        | table | postgres
 public | django_migrations          | table | postgres
 public | django_session             | table | postgres
(10 rows)

退出Postgres

postgres-# \q

2. 建立數據模型

編輯polls/models.py

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)

3. 啓動數據模型

1. 通知Prject，polls app 應用已安裝

   編輯mysite/settings.py，添加一行`'polls.apps.PollsConfig',`

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

1. 到web容器中執行命令：

$ python manage.py makemigrations polls

makemigrations 告訴Django你對模型作了些修改，並並但願保存下來。Django會建立修改腳本polls/migrations/0001_initial.py，
應該會看到相似：

Migrations for 'polls':
  polls/migrations/0001_initial.py:
    - Create model Choice
    - Create model Question
    - Add field question to choice

到此數據庫並未改變，真正執行變動而且幫助你管理數據庫模式是migration命令，能夠用以下命令查看將要執行的SQL命令

$ python manage.py sqlmigrate polls 0001

應該會看到相似（不一樣數據庫會有所不一樣）：

BEGIN;
--
-- Create model Choice
--
CREATE TABLE "polls_choice" ("id" serial NOT NULL PRIMARY KEY, "choice_text" varchar(200) NOT NULL, "votes" integer NOT NULL);
--
-- Create model Question
--
CREATE TABLE "polls_question" ("id" serial NOT NULL PRIMARY KEY, "question_text" varchar(200) NOT NULL, "pub_date" timestamp with time zone NOT NULL);
--
-- Add field question to choice
--
ALTER TABLE "polls_choice" ADD COLUMN "question_id" integer NOT NULL;
CREATE INDEX "polls_choice_question_id_c5b4b260" ON "polls_choice" ("question_id");
ALTER TABLE "polls_choice" ADD CONSTRAINT "polls_choice_question_id_c5b4b260_fk_polls_question_id" FOREIGN KEY ("question_id") REFERENCES "polls_question" ("id") DEFERRABLE INITIALLY DEFERRED;
COMMIT;

保存數據庫修改：

$ python manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, polls, sessions
Running migrations:
  Rendering model states... DONE
  Applying polls.0001_initial... OK

小結：
修改數據庫分三步：

1. 修改模型 (in models.py).
2. 執行: python manage.py makemigrations 建立一個遷移
3. 執行：python manage.py migrate 保存變動

4. API

下面進入交互式的Python Shell跟API一塊兒玩耍吧，別忘了先進入容器。

$ python manage.py shell

如需瞭解database API的相關內容：database API

可進行一下嘗試瞭解API：

>>> from polls.models import Question, Choice   # Import the model classes we just wrote.

# No questions are in the system yet.
>>> Question.objects.all()
<QuerySet []>

# 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 "1L" instead of "1", depending
# on which database you're using. That's no biggie; it just means your
# 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()
<QuerySet [<Question: Question object>]>

爲了讓<Question: Question object>輸出更可讀
給模塊Question and Choice (in the polls/models.py file) 添加 __str__() 方法

from django.db import models
from django.utils.encoding import python_2_unicode_compatible

@python_2_unicode_compatible  # only if you need to support Python 2
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):
    # ...
    def __str__(self):
        return self.choice_text

除了那些常見的Python方法，能夠添加一個自定義的

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() - datetime.timedelta(days=1)

在次進入shell看看有哪些變化：

>>> from polls.models import Question, Choice

# Make sure our __str__() addition worked.
>>> Question.objects.all()
<QuerySet [<Question: What's up?>]>

# Django provides a rich database lookup API that's entirely driven by
# keyword arguments.
>>> Question.objects.filter(id=1)
<QuerySet [<Question: What's up?>]>
>>> Question.objects.filter(question_text__startswith='What')
<QuerySet [<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: What's up?>

# Request an ID that doesn't exist, this will raise an exception.
>>> Question.objects.get(id=2)
Traceback (most recent call last):
    ...
DoesNotExist: Question matching query does not exist.

# Lookup by a primary key is the most common case, so Django provides a
# shortcut for primary-key exact lookups.
# The following is identical to Question.objects.get(id=1).
>>> Question.objects.get(pk=1)
<Question: What's up?>

# Make sure our custom method worked.
>>> q = Question.objects.get(pk=1)
>>> q.was_published_recently()
True

# Give the Question a couple of Choices. The create call constructs a new
# Choice object, does the INSERT statement, adds the choice to the set
# of available choices and returns the new Choice object. Django creates
# a set to hold the "other side" of a ForeignKey relation
# (e.g. a question's choice) which can be accessed via the API.
>>> q = Question.objects.get(pk=1)

# Display any choices from the related object set -- none so far.
>>> q.choice_set.all()
<QuerySet []>

# Create three choices.
>>> q.choice_set.create(choice_text='Not much', votes=0)
<Choice: Not much>
>>> q.choice_set.create(choice_text='The sky', votes=0)
<Choice: The sky>
>>> c = q.choice_set.create(choice_text='Just hacking again', votes=0)

# Choice objects have API access to their related Question objects.
>>> c.question
<Question: What's up?>

# And vice versa: Question objects get access to Choice objects.
>>> q.choice_set.all()
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
>>> q.choice_set.count()
3

# The API automatically follows relationships as far as you need.
# Use double underscores to separate relationships.
# This works as many levels deep as you want; there's no limit.
# Find all Choices for any question whose pub_date is in this year
# (reusing the 'current_year' variable we created above).
>>> Choice.objects.filter(question__pub_date__year=current_year)
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>

# Let's delete one of the choices. Use delete() for that.
>>> c = q.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()

5. 介紹Django Admin

1. 建立Admin用戶

$ python manage.py createsuperuser

Username: admin

Email address: admin@example.com

驗證兩次密碼：

Password: **********
Password (again): *********
Superuser created successfully.

註冊成功

2. 開始服務器開發

Django的Admin是默認激活的

啓動服務器 docker-compose up

打開： http://127.0.0.1:8000/admin/

輸入帳號密碼

3. 經過admin來管理poll應用

修改polls/admin.py 註冊Question到admin site 來告訴admin Question 已經提供了admin的接口

from django.contrib import admin

from .models import Question

admin.site.register(Question)

能夠看到以前建立的question

能夠修改

若是選擇時間Now的時候發現時間不對，那可能就是時區問題。
檢查以前的設置mysite/setting.py 例如：

#TIME_ZONE = 'UTC'
TIME_ZONE = 'Pacific/Auckland'

好了，完成第二步了