模型如下:
class Publisher(models.Model):
name = models.CharField(max_length=30)
address = models.CharField(max_length=50)
city = models.CharField(max_length=60)
state_province = models.CharField(max_length=30)
country = models.CharField(max_length=50)
website = models.URLField() class Author(models.Model):
first_name = models.CharField(max_length=30)
last_name = models.CharField(max_length=40)
email = models.EmailField() class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
查看生成sql用>python manage.py sqlmigrate,
生成sql:
BEGIN;
--下面来解释自动生成的sql语句,生成的sql顺序比较乱,已经整理了一下 CREATE TABLE `posts_author` (
`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
`first_name` varchar(30) NOT NULL,
`last_name` varchar(40) NOT NULL,
`email` varchar(254) NOT NULL);
--
--
-- CREATE TABLE `posts_book` (
`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
`title` varchar(100) NOT NULL,
`publication_date` date NOT NULL);
--
CREATE TABLE `posts_book_authors` (
`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
`book_id` integer NOT NULL,
`author_id` integer NOT NULL);
--
-- 这个表是没有在models中定义的,只是因为authors = models.ManyToManyField(Author)
-- django就创建了一个表(多对多连接表)来处理书籍和作者之间的映射关系
--这也是数据库设计的原则,这样能较少冗余。不然的话,比如说一本书有多个作者,这个表就会重复多条数据(除了作者不同)
--
CREATE TABLE `posts_publisher` (
`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
`name` varchar(30) NOT NULL,
`address` varchar(50) NOT NULL,
`city` varchar(60) NOT NULL,
`state_province` varchar(30) NOT NULL,
`country` varchar(50) NOT NULL,
`website` varchar(200) NOT NULL);
--
-- 上面分别创建的表,因为模型没有指明关键字,所以自动创建id为关键字
--
ALTER TABLE `posts_book` ADD COLUMN `publisher_id` integer NOT NULL;
ALTER TABLE `posts_book` ALTER COLUMN `publisher_id` DROP DEFAULT;
ALTER TABLE `posts_book` ADD CONSTRAINT `posts_book_publisher_id_4475e105_fk_posts_publisher_id` FOREIGN KEY (`publisher_id`) REFERENCES `posts_publisher` (`id`);
--
-- publisher = models.ForeignKey(Publisher)
-- 这句话的意思是‘参考类Publisher(也就是表posts_publisher)’
-- 创建外键,表Publisher主键是id,所以会自动加上一个字段publisher_id
-- 最后就是在表posts_book 中增加外键 `posts_publisher` (`id`)
--
ALTER TABLE `posts_book_authors` ADD CONSTRAINT `posts_book_authors_book_id_1487a223_fk_posts_book_id` FOREIGN KEY (`book_id`) REFERENCES `posts_book` (`id`);
ALTER TABLE `posts_book_authors` ADD CONSTRAINT `posts_book_authors_author_id_0a9b3d34_fk_posts_author_id` FOREIGN KEY (`author_id`) REFERENCES `posts_author` (`id`);
ALTER TABLE `posts_book_authors` ADD CONSTRAINT `posts_book_authors_book_id_7d4dbc86_uniq` UNIQUE (`book_id`, `author_id`);
--
-- 这里又创建了两个外键,都是中间表‘外键’其他两个表,分别是
-- 表posts_book_authors(book_id) 外键 posts_book(id)
-- 表posts_book_authors(author_id) 外键 posts_author(id)
-- 最后做了唯一性约束
--
CREATE INDEX `posts_book_2604cbea` ON `posts_book` (`publisher_id`);
--
--可以看出,都是表创建完成后,才进行外键设置操作
--
COMMIT;