Python 数据库操作 SQLAlchemy的示例代码(2)-木庄网络博客

SQLAlchemy 通过 query 来对数据进行查询，可以通过 filter 方法对查询结果进行筛选。

user = session.query(User).filter(User.id<2).all()
print(user)
user = session.query(User).filter(User.id<=5).all()
print(user)

以上代码通过 query 获取数据库中所有 User 数据，然后通过 filter 方法筛选出 id 小于 2 和 id 小于等于 5 的数据。

数据库的修改可以通过 merge 和 update 来实现

user1.name = 'admin'
session.merge(user1)
user4 = User(name='fred', fullname='Fred Flintstone', nickname='freddy')
session.merge(user4)
session.query(User).filter(User.id==2).update({'name':'test'})
user = session.query(User).filter(User.id<=5).all()
print(user)

使用 merge 修改数据，当数据中存在该数据时修改，不存在是将当前数据插入数据库中。

代码运行结果

以上示例代码的运行结果如下

2019-02-16 21:45:23,919 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1
2019-02-16 21:45:23,919 INFO sqlalchemy.engine.base.Engine ()
2019-02-16 21:45:23,919 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1
2019-02-16 21:45:23,919 INFO sqlalchemy.engine.base.Engine ()
2019-02-16 21:45:23,920 INFO sqlalchemy.engine.base.Engine PRAGMA table_info("users")
2019-02-16 21:45:23,920 INFO sqlalchemy.engine.base.Engine ()
2019-02-16 21:45:23,921 INFO sqlalchemy.engine.base.Engine
CREATE TABLE users (
  id INTEGER NOT NULL,
  name VARCHAR,
  fullname VARCHAR,
  nickname VARCHAR,
  PRIMARY KEY (id)
)


2019-02-16 21:45:23,921 INFO sqlalchemy.engine.base.Engine ()
2019-02-16 21:45:23,922 INFO sqlalchemy.engine.base.Engine COMMIT
2019-02-16 21:45:23,924 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2019-02-16 21:45:23,925 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, nickname) VALUES (?, ?, ?)
2019-02-16 21:45:23,925 INFO sqlalchemy.engine.base.Engine ('ed', 'Ed Jones', 'edsnickname')
2019-02-16 21:45:23,926 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, nickname) VALUES (?, ?, ?)
2019-02-16 21:45:23,926 INFO sqlalchemy.engine.base.Engine ('wendy', 'Wendy Williams', 'windy')
2019-02-16 21:45:23,926 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, nickname) VALUES (?, ?, ?)
2019-02-16 21:45:23,926 INFO sqlalchemy.engine.base.Engine ('mary', 'Mary Contrary', 'mary')
2019-02-16 21:45:23,927 INFO sqlalchemy.engine.base.Engine COMMIT
2019-02-16 21:45:23,929 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2019-02-16 21:45:23,929 INFO sqlalchemy.engine.base.Engine SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.nickname AS users_nickname
FROM users
WHERE users.id < ?
2019-02-16 21:45:23,929 INFO sqlalchemy.engine.base.Engine (2,)
[<User(name='ed', fullname='Ed Jones', nickname='edsnickname')>]
2019-02-16 21:45:23,931 INFO sqlalchemy.engine.base.Engine SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.nickname AS users_nickname
FROM users
WHERE users.id <= ?
2019-02-16 21:45:23,931 INFO sqlalchemy.engine.base.Engine (5,)
[<User(name='ed', fullname='Ed Jones', nickname='edsnickname')>, <User(name='wendy', fullname='Wendy Williams', nickname='windy')>, <User(name='mary', fullname='Mary Contrary', nickname='mary')>]
2019-02-16 21:45:23,932 INFO sqlalchemy.engine.base.Engine UPDATE users SET name=? WHERE users.id = ?
2019-02-16 21:45:23,932 INFO sqlalchemy.engine.base.Engine ('admin', 1)
2019-02-16 21:45:23,933 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, nickname) VALUES (?, ?, ?)
2019-02-16 21:45:23,933 INFO sqlalchemy.engine.base.Engine ('fred', 'Fred Flintstone', 'freddy')
2019-02-16 21:45:23,934 INFO sqlalchemy.engine.base.Engine UPDATE users SET name=? WHERE users.id = ?
2019-02-16 21:45:23,934 INFO sqlalchemy.engine.base.Engine ('test', 2)
2019-02-16 21:45:23,935 INFO sqlalchemy.engine.base.Engine SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.nickname AS users_nickname
FROM users
WHERE users.id <= ?
2019-02-16 21:45:23,935 INFO sqlalchemy.engine.base.Engine (5,)
[<User(name='admin', fullname='Ed Jones', nickname='edsnickname')>, <User(name='test', fullname='Wendy Williams', nickname='windy')>, <User(name='mary', fullname='Mary Contrary', nickname='mary')>, <User(name='fred', fullname='Fred Flintstone', nickname='freddy')>]

由于我们设置 create_engine 中 echo 为 True，因此在执行结果中包含了 SQLAlchemy 打印的 SQL 语句，我们可以取消 crete_engine 中的 echo

engine = create_engine('sqlite:///./sqlalchemy.sqlite')

此时的执行结果如下：

[<User(name='ed', fullname='Ed Jones', nickname='edsnickname')>]
[<User(name='ed', fullname='Ed Jones', nickname='edsnickname')>, <User(name='wendy', fullname='Wendy Williams', nickname='windy')>, <User(name='mary', fullname='Mary Contrary', nickname='mary')>]
[<User(name='admin', fullname='Ed Jones', nickname='edsnickname')>, <User(name='test', fullname='Wendy Williams', nickname='windy')>, <User(name='mary', fullname='Mary Contrary', nickname='mary')>, <User(name='fred', fullname='Fred Flintstone', nickname='freddy')>]

当取消 echo 后，程序运行结果中原有的 SQL 语句消失。

本文只是对 SQLAlchemy 的使用进行简单的介绍，SQLAlchemy 本身还有很多特性和运用方法我们可以共同探讨。

标签：SQLite

返回前面的内容