Python中使用SQLAlchemy连接Mysql数据库（单表操作）

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