本文主要是介绍Python中使用SQLAlchemy连接Mysql数据库（单表操作），希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
一，SQLAlchemy的安装
使用
$ easy_install sqlalchemy
或
$ pip install sqlalchemy
如果出现什么错，就进去root用户下进行安装试试，或者网上查查
>>> import sqlalchemy
>>>
这样说明成功了，切记是小写哦
二，使用
理论我也不懂，自己查查资料，现在用一个小的案例说一下使用步骤
1，在进行数据操作之前要先连上数据库。
>>> from sqlalchemy import create_engine
>>> from sqlalchemy.orm import sessionmaker
>>> DB_CONNECT = 'mysql+mysqldb://root:102@localhost/mydb'
>>> engine = create_engine(DB_CONNECT, echo=True)
>>> DB_Session = sessionmaker(bind=engine)
>>> session = DB_Session()from 是从sqlalchemy中插入必须的模板，DB_CONNECT 是构造数据库的路径 ，mysql+mysqldb是说明使用MySQL-Python 来连接，root是数据库用户名，102是密码，localhost表示是数据库在本机上，mydb是要连接的数据库名字，设置字符集的charset可以省了
create_engine() 会返回一个数据库引擎，echo 参数为 True 时，会显示每条执行的 SQL 语句，生产环境下可关闭。
sessionmaker(bind=engine)会生成一个数据库会话类。这个类的实例可以当成一个数据库连接，它同时还记录了一些查询的数据，并决定什么时候执行 SQL 语句。由于 SQLAlchemy 自己维护了一个数据库连接池（默认 5 个连接），也可以自己设置。
得到session 后，就可以执行 SQL 了：
2，在进行操作前先把表给建立了，由于SQLAlchemy 可以和变进行建立连接并且可以通过语言进行见表
mysql> show tables;
Empty set (0.00 sec)
mysql>
此时是没有表的，现在我们建立一个学生便stu，一个课程表cla和一个成绩表grade
>>> from sqlalchemy import Column
>>> from sqlalchemy.types import CHAR, Integer, String
>>> from sqlalchemy.ext.declarative import declarative_base
>>> from random import randint
>>> from sqlalchemy import ForeignKey
>>> BaseModel = declarative_base()
>>> def init_db():
... BaseModel.metadata.create_all(engine)
...
>>> def drop_db():
... BaseModel.metadata.drop_all()
...
>>> class Stu(BaseModel):
... __tablename__='stu'
... id = Column(Integer,primary_key = True)
... name = Column(CHAR(30))
...
>>> class Cla(BaseModel):
... __tablename__='cla'
... id = Column(Integer,primary_key = True)设置主键
... cname = Column(CHAR(30))
...
>>> class Grade(BaseModel):
... __tablename__ = 'grade'
... uid = Column(Integer,ForeignKey('stu.id'))设置外键
... cid = Column(Integer,ForeignKey('cla.id'))
... id = Column(Integer,primary_key=True)
... gre=Column(Integer)
...
declarative_base() 创建了一个 BaseModel 类，这个类的子类可以自动与一个表关联。以 Stu 类为例，它的 tablename 属性就是数据库中该表的名称，它有 id 和 name 这两个字段，分别为整型和 30 个定长字符。Column 还有一些其他的参数，我就不解释了。
最后，BaseModel.metadata.create_all(engine) 会找到 BaseModel 的所有子类，并在数据库中建立这些表；drop_all() 则是删除这些表。
现在执行init_db()进行建立表，对应语句如下
>>> init_db()
CREATE TABLE stu (id INTEGER NOT NULL AUTO_INCREMENT, name CHAR(30), PRIMARY KEY (id)
)CREATE TABLE cla (id INTEGER NOT NULL AUTO_INCREMENT, cname CHAR(30), PRIMARY KEY (id)
)
CREATE TABLE grade (id INTEGER NOT NULL AUTO_INCREMENT, uid INTEGER, cid INTEGER, gre INTEGER, PRIMARY KEY (id), FOREIGN KEY(uid) REFERENCES stu (id), FOREIGN KEY(cid) REFERENCES cla (id)
)
COMMIT
>>>
以上就是执行时对应的建表语句，现在去数据库看看表是否存在，并查看一个表结构
mysql> show tables;
+----------------+
| Tables_in_mydb |
+----------------+
| cla |
| grade |
| stu |
+----------------+
3 rows in set (0.00 sec)表已经建立成功了，现在看一下表结构
mysql> desc grade;
+-------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| uid | int(11) | YES | MUL | NULL | |
| cid | int(11) | YES | MUL | NULL | |
| gre | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
可以看出 使用SQLAlchemy中的语句和使用SQL语句的结果一样。接下来就可以插入数据了
>>> stu = Stu(name='a')
>>> session.add(stu)
>>> stu = Stu(name='b')
>>> session.add(stu)
>>> stu = Stu(name='c')
>>> session.add(stu)
>>> stu = Stu(name='d')
>>> session.add(stu)
>>> stu = Stu(name='e')
>>> session.add(stu)
>>> 手动插入了五条记录，但此时还没有提交，没有真正的写入数据库
或者使用非ORM方式进行插入
>>>session.execute(Stu.__table__.insert(),[{'name':randint(1,100)} for i in xrange(10000)])
>>>session.commit()
#可以速度更快的插入更多的数据
>>> session.commit()
2016-05-09 18:22:16,839 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-05-09 18:22:16,840 INFO sqlalchemy.engine.base.Engine INSERT INTO stu (name) VALUES (%s)
2016-05-09 18:22:16,840 INFO sqlalchemy.engine.base.Engine ('a',)
2016-05-09 18:22:16,841 INFO sqlalchemy.engine.base.Engine INSERT INTO stu (name) VALUES (%s)
2016-05-09 18:22:16,841 INFO sqlalchemy.engine.base.Engine ('b',)
2016-05-09 18:22:16,841 INFO sqlalchemy.engine.base.Engine INSERT INTO stu (name) VALUES (%s)
2016-05-09 18:22:16,841 INFO sqlalchemy.engine.base.Engine ('c',)
2016-05-09 18:22:16,842 INFO sqlalchemy.engine.base.Engine INSERT INTO stu (name) VALUES (%s)
2016-05-09 18:22:16,842 INFO sqlalchemy.engine.base.Engine ('d',)
2016-05-09 18:22:16,842 INFO sqlalchemy.engine.base.Engine INSERT INTO stu (name) VALUES (%s)
2016-05-09 18:22:16,842 INFO sqlalchemy.engine.base.Engine ('e',)
2016-05-09 18:22:16,843 INFO sqlalchemy.engine.base.Engine COMMIT
>>>
此时真的写入数据库了哦。向课程表插入五条
>>> cla = Cla(cname='yuwen')
>>> session.add(cla)
>>> cla = Cla(cname='shuxue')
>>> session.add(cla)
>>> cla = Cla(cname='yingyu')
>>> session.add(cla)
>>> cla = Cla(cname='wuli')
>>> session.add(cla)
>>> cla = Cla(cname='huaxue')
>>> session.add(cla)
>>> session.commit()
3,现在开始操作数据
>>> query = session.query(Stu)
>>> for st in query:
... print st.name
...
对应的SQL语句
SELECT stu.id AS stu_id, stu.name AS stu_name
FROM stu
2016-05-09 18:56:07,084 INFO sqlalchemy.engine.base.Engine ()
a
b
c
d
e
>>> print query.all()# # 返回的是一个类似列表的对象
SELECT stu.id AS stu_id, stu.name AS stu_name
FROM stu
2016-05-09 18:58:16,085 INFO sqlalchemy.engine.base.Engine ()
[<__main__.Stu object at 0xb66b3f4c>, <__main__.Stu object at 0xb5e4202c>, <__main__.Stu object at 0xb66b3f8c>, <__main__.Stu object at 0xb5e4206c>, <__main__.Stu object at 0xb6688c0c>]>>> print query.first().name# 有数据时返回第一条记录，没有数据时会返回 None
SELECT stu.id AS stu_id, stu.name AS stu_name
FROM stu LIMIT %s
2016-05-09 18:59:43,149 INFO sqlalchemy.engine.base.Engine (1,)
a
# print query.one().name# 不存在，或有多行记录时会抛出异常>>> print query.filter(Stu.id == 2).first().name
SELECT stu.id AS stu_id, stu.name AS stu_name
FROM stu
WHERE stu.id = %s LIMIT %s
2016-05-09 19:04:54,363 INFO sqlalchemy.engine.base.Engine (2, 1)
b
>>> print query.filter('id = 2').first().name # 支持字符串
SELECT stu.id AS stu_id, stu.name AS stu_name
FROM stu
WHERE id = 2 LIMIT %s
2016-05-09 19:07:02,016 INFO sqlalchemy.engine.base.Engine (1,)
b
>>> print query.get(2).name # 以主键获取，等效于上句
2016-05-09 19:07:40,007 INFO sqlalchemy.engine.base.Engine SELECT stu.id AS stu_id, stu.name AS stu_name
FROM stu
WHERE stu.id = %s
2016-05-09 19:07:40,007 INFO sqlalchemy.engine.base.Engine (2,)
b
>>> print query.get(2).id
SELECT stu.id AS stu_id, stu.name AS stu_name
FROM stu
WHERE stu.id = %s
2016-05-09 19:08:46,009 INFO sqlalchemy.engine.base.Engine (2,)
2
>>> quer2 = session.query(Stu.name)
>>> print quer2.all()
SELECT stu.name AS stu_name
FROM stu
2016-05-09 19:09:46,259 INFO sqlalchemy.engine.base.Engine ()
[('a',), ('b',), ('c',), ('d',), ('e',)]
>>> print quer2.limit(1).all() #只返回一条
2016-05-09 19:11:23,383 INFO sqlalchemy.engine.base.Engine SELECT stu.name AS stu_name
FROM stu LIMIT %s
2016-05-09 19:11:23,383 INFO sqlalchemy.engine.base.Engine (1,)
[('a',)]>>> print quer2.limit(2).all()#只返回两条
SELECT stu.name AS stu_name
FROM stu LIMIT %s
2016-05-09 19:11:29,480 INFO sqlalchemy.engine.base.Engine (2,)
[('a',), ('b',)]
>>> print quer2.offset(1).all() #跳过一条，从第二条数据开始查询
SELECT stu.name AS stu_name
FROM stu LIMIT %s, 18446744073709551615
2016-05-09 19:13:25,734 INFO sqlalchemy.engine.base.Engine (1,)
[('b',), ('c',), ('d',), ('e',)]
>>> print quer2.offset(3).all() #从第四条数据开始
SELECT stu.name AS stu_name
FROM stu LIMIT %s, 18446744073709551615
2016-05-09 19:13:39,629 INFO sqlalchemy.engine.base.Engine (3,)
[('d',), ('e',)]
#按name降序排序
>>> print quer2.order_by(Stu.name.desc()).all()
SELECT stu.name AS stu_name
FROM stu ORDER BY stu.name DESC
2016-05-09 19:16:56,022 INFO sqlalchemy.engine.base.Engine ()
[('e',), ('d',), ('c',), ('b',), ('a',)]>>> print quer2.order_by('name desc').all()
SELECT stu.name AS stu_name
FROM stu ORDER BY name desc
2016-05-09 19:17:09,851 INFO sqlalchemy.engine.base.Engine ()
[('e',), ('d',), ('c',), ('b',), ('a',)]
#按name降序，有重复的按id升序排序
>>> print session.query(Stu.id).order_by('name desc','id').all()
SELECT stu.id AS stu_id
FROM stu ORDER BY name desc, stu.id
2016-05-09 19:20:34,818 INFO sqlalchemy.engine.base.Engine ()
[(5L,), (4L,), (3L,), (2L,), (1L,)]
#scalar()在有多条数据时使用报出异常,all()可以使用多条也可以使用一条
#>>> print quer2.filter(Stu.id>2).scalar()
>>> print quer2.filter(Stu.id>2).all()
SELECT stu.name AS stu_name
FROM stu
WHERE stu.id > %s
2016-05-09 19:56:47,760 INFO sqlalchemy.engine.base.Engine (2,)
[('c',), ('d',), ('e',)]>>> print quer2.filter(Stu.id==2).all()
SELECT stu.name AS stu_name
FROM stu
WHERE stu.id = %s
2016-05-09 19:57:47,901 INFO sqlalchemy.engine.base.Engine (2,)
[('b',)]>>> print quer2.filter(Stu.id==2).scalar()
SELECT stu.name AS stu_name
FROM stu
WHERE stu.id = %s
2016-05-09 19:23:38,761 INFO sqlalchemy.engine.base.Engine (2,)
b>>> print quer2.filter('id=2').scalar()
SELECT stu.name AS stu_name
FROM stu
WHERE id=2
2016-05-09 19:43:47,797 INFO sqlalchemy.engine.base.Engine ()
b#在此中‘，’等价于and
>>> print query2.filter(Stu.id>1,Stu.name !='a').first()
SELECT stu.name AS stu_name
FROM stu
WHERE stu.id > %s AND stu.name != %s LIMIT %s
2016-05-09 19:51:14,571 INFO sqlalchemy.engine.base.Engine (1, 'a', 1)
('b',)
>>> #此种迭代也类似与and
>>> query3 = query2.filter(Stu.id>1)
>>> query3 = query3.filter(Stu.name != 'a')
>>> query3.first()
2016-05-09 19:53:50,150 INFO sqlalchemy.engine.base.Engine SELECT stu.name AS stu_name
FROM stu
WHERE stu.id > %s AND stu.name != %s LIMIT %s
2016-05-09 19:53:50,151 INFO sqlalchemy.engine.base.Engine (1, 'a', 1)
('b',)#or_就是类似or
>>> print query2.filter(or_(Stu.id == 1,Stu.id==2)).all()
2016-05-09 19:55:59,383 INFO sqlalchemy.engine.base.Engine SELECT stu.name AS stu_name
FROM stu
WHERE stu.id = %s OR stu.id = %s
2016-05-09 19:55:59,383 INFO sqlalchemy.engine.base.Engine (1, 2)
[('a',), ('b',)]# in的用法
>>> print query2.filter(Stu.id.in_((1,2,3))).all()
SELECT stu.name AS stu_name
FROM stu
WHERE stu.id IN (%s, %s, %s)
2016-05-09 20:01:01,729 INFO sqlalchemy.engine.base.Engine (1, 2, 3)
[('a',), ('b',), ('c',)]
>>> #为null的一些用法
>>> query4 = session.query(Stu.id)
>>> print query4.filter(Stu.name==None).scalar()
SELECT stu.id AS stu_id
FROM stu
WHERE stu.name IS NULL
2016-05-09 20:02:59,821 INFO sqlalchemy.engine.base.Engine ()
None
>>>
>>> print query4.filter('name is null').scalar()
SELECT stu.id AS stu_id
FROM stu
WHERE name is null
2016-05-09 20:03:40,312 INFO sqlalchemy.engine.base.Engine ()
None
>>> #不为null的一些用法
>>> print query4.filter(not_(Stu.name == None)).all()
SELECT stu.id AS stu_id
FROM stu
WHERE stu.name IS NOT NULL
2016-05-09 20:04:49,888 INFO sqlalchemy.engine.base.Engine ()
[(1L,), (2L,), (3L,), (4L,), (5L,)]
>>> >>> print query4.filter(Stu.name != None).all()
SELECT stu.id AS stu_id
FROM stu
WHERE stu.name IS NOT NULL
2016-05-09 20:05:42,724 INFO sqlalchemy.engine.base.Engine ()
[(1L,), (2L,), (3L,), (4L,), (5L,)]
>>>
#func条用各种函数的用法>>> print query4.count()
SELECT count(*) AS count_1
FROM (SELECT stu.id AS stu_id
FROM stu) AS anon_1
2016-05-09 20:08:43,352 INFO sqlalchemy.engine.base.Engine ()
5>>> print session.query(func.count('*')).select_from(Stu).scalar()SELECT count(%s) AS count_1
FROM stu
2016-05-09 20:08:43,356 INFO sqlalchemy.engine.base.Engine ('*',)
5>>> print session.query(func.count('1')).select_from(Stu).scalar()
SELECT count(%s) AS count_1
FROM stu
2016-05-09 20:08:43,362 INFO sqlalchemy.engine.base.Engine ('1',)
5>>> print session.query(func.count(Stu.id)).scalar()
SELECT count(stu.id) AS count_1
FROM stu
2016-05-09 20:08:43,369 INFO sqlalchemy.engine.base.Engine ()
5>>> print session.query(func.count('*')).filter(Stu.id > 0).scalar() # filter()中包含Stu，因此不需要指定表
SELECT count(%s) AS count_1
FROM stu
WHERE stu.id > %s
2016-05-09 20:08:43,377 INFO sqlalchemy.engine.base.Engine ('*', 0)
5>>> print session.query(func.count('*')).filter(Stu.name == 'a').limit(1).scal() == 1 # 可以用 limit() 限制 count() 的返回数
SELECT count(%s) AS count_1
FROM stu
WHERE stu.name = %s LIMIT %s
2016-05-09 20:08:43,394 INFO sqlalchemy.engine.base.Engine ('*', 'a', 1)
True>>> print session.query(func.sum(Stu.id)).scalar()
SELECT sum(stu.id) AS sum_1
FROM stu
2016-05-09 20:08:43,401 INFO sqlalchemy.engine.base.Engine ()
15>>> print session.query(func.now()).scalar() # func 后可以跟任意函数名，只要该据库支持
SELECT now() AS now_1
2016-05-09 20:08:43,406 INFO sqlalchemy.engine.base.Engine ()
2016-05-09 20:08:43>>> print session.query(func.current_timestamp()).scalar()
SELECT CURRENT_TIMESTAMP AS current_timestamp_1
2016-05-09 20:08:43,411 INFO sqlalchemy.engine.base.Engine ()
2016-05-09 20:08:43>>> print session.query(func.md5(Stu.name)).filter(Stu.id == 1).scalar()
SELECT md5(stu.name) AS md5_1
FROM stu
WHERE stu.id = %s
2016-05-09 20:08:44,841 INFO sqlalchemy.engine.base.Engine (1,)
0cc175b9c0f1b6a831c399e269772661
>>> #修改数据
>>> query.filter(Stu.id==1).update({Stu.name:'li'})
UPDATE stu SET name=%s WHERE stu.id = %s
2016-05-09 20:12:57,027 INFO sqlalchemy.engine.base.Engine ('li', 1)
1L#删除数据
>>> query = session.query(Grade)
>>> query.filter(Grade.id == 1).delete()
DELETE FROM grade WHERE grade.id = %s
2016-05-09 20:28:18,638 INFO sqlalchemy.engine.base.Engine (1,)
1L
>>>
此时没有提交，在数据库中环视存在的
mysql> select * from grade;
+----+------+------+------+
| id | uid | cid | gre |
+----+------+------+------+
| 1 | 1 | 1 | 60 |
| 2 | 2 | 1 | 66 |
| 3 | 5 | 1 | 66 |
| 4 | 5 | 5 | 96 |
| 5 | 5 | 3 | 96 |
| 6 | 3 | 2 | 96 |
| 7 | 3 | 4 | 76 |
| 8 | 4 | 4 | 76 |
| 9 | 4 | 3 | 76 |
| 10 | 4 | 5 | 76 |
| 11 | 1 | 4 | 76 |
| 12 | 1 | 5 | 76 |
| 13 | 2 | 5 | 76 |
| 14 | 3 | 3 | 60 |
| 15 | 2 | 3 | 50 |
+----+------+------+------+
15 rows in set (0.00 sec)
#开始提交
>>> session.commit()
2016-05-09 20:31:02,461 INFO sqlalchemy.engine.base.Engine COMMIT
>>>
mysql> select * from grade;
+----+------+------+------+
| id | uid | cid | gre |
+----+------+------+------+
| 2 | 2 | 1 | 66 |
| 3 | 5 | 1 | 66 |
| 4 | 5 | 5 | 96 |
| 5 | 5 | 3 | 96 |
| 6 | 3 | 2 | 96 |
| 7 | 3 | 4 | 76 |
| 8 | 4 | 4 | 76 |
| 9 | 4 | 3 | 76 |
| 10 | 4 | 5 | 76 |
| 11 | 1 | 4 | 76 |
| 12 | 1 | 5 | 76 |
| 13 | 2 | 5 | 76 |
| 14 | 3 | 3 | 60 |
| 15 | 2 | 3 | 50 |
+----+------+------+------+
14 rows in set (0.00 sec)也获取不到对象了
>>> print query.get(1)
SELECT grade.id AS grade_id, grade.uid AS grade_uid, grade.cid AS grade_cid, grade.gre AS grade_gre
FROM grade
WHERE grade.id = %s
2016-05-09 20:32:20,742 INFO sqlalchemy.engine.base.Engine (1,)
None
>>>
单表的增删改查完事了，下面来看看多表连接操作
http://blog.csdn.net/u011573853/article/details/51363780
一些细节会在下面进行说明（事务，加锁，编码等）
http://blog.csdn.net/u011573853/article/details/51366124
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