Django 数据库操作相关

Posted 2020-10-22 dion至君

当我们在Django项目中的models.py下写好创建表的代码后。为了创建好这些数据库表，我们再一次请出我的工程管理助手 manage.py。激活虚拟环境，切换到 manage.py 文件所在的目录下，分别运行 python manage.py makemigrations 和 python manage.py migrate 命令：

F:\myblog>python manage.py makemigrations
Migrations for ‘blog‘:
  blog\migrations\0001_initial.py
    - Create model Category
    - Create model Post
    - Create model Tag
    - Add field tags to post

F:\myblog>python manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, blog, contenttypes, sessions
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying admin.0002_logentry_remove_auto_add... OK
  Applying contenttypes.0002_remove_content_type_name... OK
  Applying auth.0002_alter_permission_name_max_length... OK
  Applying auth.0003_alter_user_email_max_length... OK
  Applying auth.0004_alter_user_username_opts... OK
  Applying auth.0005_alter_user_last_login_null... OK
  Applying auth.0006_require_contenttypes_0002... OK
  Applying auth.0007_alter_validators_add_error_messages... OK
  Applying auth.0008_alter_user_username_max_length... OK
  Applying blog.0001_initial... OK
  Applying sessions.0001_initial... OK

然后我们可以具体查看终端里Django究竟是做了什么为我们创建数据表的？实际是通过ORM将Python命令翻译为SQL语言，操作数据库。

F:\myblog>python manage.py sqlmigrate blog 0001
BEGIN;
--
-- Create model Category
--
CREATE TABLE `blog_category` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `name` varchar(100) NOT NULL);
--
-- Create model Post
--
CREATE TABLE `blog_post` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `title` varchar(70) NOT NULL, `body` longtext NOT NULL, `created_time` datetime(6) NOT NULL, `modified_time` datetime(6) NOT NULL, `
excerpt` varchar(200) NOT NULL, `author_id` integer NOT NULL, `category_id` integer NOT NULL);
--
-- Create model Tag
--
CREATE TABLE `blog_tag` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `name` varchar(100) NOT NULL);
--
-- Add field tags to post
--
CREATE TABLE `blog_post_tags` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `post_id` integer NOT NULL, `tag_id` integer NOT NULL);
ALTER TABLE `blog_post` ADD CONSTRAINT `blog_post_author_id_dd7a8485_fk_auth_user_id` FOREIGN KEY (`author_id`) REFERENCES `auth_user` (`id`);
ALTER TABLE `blog_post` ADD CONSTRAINT `blog_post_category_id_c326dbf8_fk_blog_category_id` FOREIGN KEY (`category_id`) REFERENCES `blog_category` (`id`);
ALTER TABLE `blog_post_tags` ADD CONSTRAINT `blog_post_tags_post_id_a1c71c8a_fk_blog_post_id` FORE
ALTER TABLE `blog_post_tags` ADD CONSTRAINT `blog_post_tags_tag_id_0875c551_fk_blog_tag_id` FOREIG
ALTER TABLE `blog_post_tags` ADD CONSTRAINT `blog_post_tags_post_id_tag_id_4925ec37_uniq` UNIQUE (
COMMIT;

查看这些SQL命令可以帮助我们理解Django的ORM运行机制。

 

在 manage.py 所在目录下运行 python manage.py shell 命令：

(blogproject_env) C:\Users\yangxg\Workspace\blogproject>python manage.py shell
Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:18:55) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>>

这就打开了交互命令行。我们可以在其中具体添加数据表的信息。

>>> from blog.models import Category, Tag, Post
>>> c = Category(name=‘category test‘)
>>> c.save()
>>> t = Tag(name=‘tag test‘)
>>> t.save()

比如在这里实例化了一个 Category 类和一个 Tag 类，为他们的属性 name 赋了值。为了让 Django 把这些数据保存进数据库，调用实例的 save 方法即可。