peewee 一个轻量级的ORM（一）

peewee是一个轻量级的ORM，sf、github上都有。用的是大名鼎鼎的sqlalchemy内核，做了一个简单的包装，用纯python编写，显得十分轻便。

废话不多说，上 直接sudo pip install peewee即可。

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from peewee import *

db = SqliteDatabase('test.db')#peewee.SqliteDatabase

# create a base model class that our application's models will extend,这样我们后面的blog与entry就链接的是同一个数据库了。这个是从django借鉴来的
class BaseModel(Model):
class Meta:
database = db

class Blog(BaseModel):#创建表，Blog：表名，name：字段，CharField：字段类型，其实就是varchar。peewee.CharField
name = CharField() # <-- VARCHAR

class Entry(BaseModel):
headline = CharField()
content = TextField() # <-- TEXT
pub_date = DateTimeField() # <-- DATETIME
blog = ForeignKeyField(Blog) # <-- INTEGER referencing the Blog table

创建表

#建立连接
db.connect()

# 建立表
Blog.create_table()
Entry.create_table()

注意：严格来说，不是一定要connect()的，但这是一个好习惯

创建模型实例（实例化）

在我们的交互式脚本编辑器那试试吧，这样能立即看出效果

Use the
Model.create() classmethod:

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>>> blog = Blog.create(name='Funny pictures of animals blog')
>>> entry = Entry.create(
... headline='maru the kitty',
... content='http://www.youtube.com/watch?v=xdhLQCYQ-nQ',
... pub_date=datetime.datetime.now(),
... blog=blog
... )

>>> entry.blog.name
'Funny pictures of animals blog'

或者是仿照编程语言的方式进行实例化:

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>>> blog = Blog()#blog就是我们实例化的对象，而Blog就是刚才声明的class
>>> blog.name = 'Another sweet blog'
>>> blog.save()

Traversing foriegn keys通过外键访问

比如我们上面那个例子

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>>> entry.blog.name
'Funny pictures of animals blog'

还可以逆转过来:

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>>> for entry in blog.entry_set:#这个entry_set没太搞懂
... print entry.headline
...
maru the kitty

在我们这个peewee引擎中，entry_set是一个 SelectQuery:

>>> blog.entry_set
<peewee.SelectQuery object at 0x151f510>

>>> blog.entry_set.sql()
('SELECT * FROM entry WHERE blog_id = ?', [1])

Model options

还可用多几个数据库

from peewee import *

custom_db = SqliteDatabase('custom.db')

class CustomModel(Model#这种元类
class Meta:
database = custom_db
):

meta是给引擎提示。引擎要执行一个sql语句的时候，要在那个数据库上执行呢，那就找到这个表所在的class继承的是那个元类

Note
Meta类中除了定义database之外还有其他几个属性。如下

database: 确定要用那个库

db_table: the name of the database table this model maps to，映射到哪张表

indexes: 一个索引的列表

ordering: a sequence of columns to use as the default ordering for this model

pk_sequence: 主键的名称队列(如果后端支持这种列表的话，peewee 可能会自动创建主键).

下面举一些例子

Specifying indexes:

class Transaction(Model):
from_acct = CharField()
to_acct = CharField()
amount = DecimalField()
date = DateTimeField()

class Meta:
indexes = (
# create a unique on from/to/date
(('from_acct', 'to_acct', 'date'), True),#索引，True的话，索引唯一，False则不唯一

# create a non-unique on from/to
(('from_acct', 'to_acct'), False),
)

Example of ordering:

class Entry(Model):
title = CharField()
body = TextField()
created = DateTimeField()

class Meta:
# order by created date descending, then title ascending
ordering = (('created', 'desc'), 'title')

Model methods对数据表操作的方法

class Model
save([force_insert=False])到底是save还是creating还是updating，这取决于这个表有木有主键。倘若force_insert设置为True，顾名思义，无论如何都会进行插入操作

example:

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>>> some_obj.title = 'new title' # <-- does not touch the database
>>> some_obj.save() # <-- 数据持久化

classmethod
create(**attributes)

Parameters:	attributes – 键值对

Create an instance of the Model with the given attributes set.

example:

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>>> user = User.create(username='admin', password='test')

delete_instance([recursive=False])
删除我们指定的例子。 如果外键设置成级连的，也会被删除. For more programmatic control,you can call with recursive=True, which will delete any non-nullablerelated models (those thatare nullable will be set to NULL).

example:

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>>> some_obj.delete_instance() # <-- it is gone forever

classmethod
filter(*args, **kwargs)#过滤操作，

Parameters:	args – a list of Q or Node objects kwargs – a mapping of column + lookup to value, e.g. “age__gt=55”
Return type:	SelectQuery with appropriate WHERE clauses

这是一个很像django的方法. 在
filter() andSelectQuery.where()二者之中的区别就是filter()
支持链式过滤

>>> sq = Entry.filter(blog__title='Some Blog')

This method is chainable:

[python] view plaincopy>>> base_q = User.filter(active=True)
>>> some_user = base_q.filter(username='charlie')

classmethod
get(*args, **kwargs)

Parameters:	args – a list of Q or Node objects kwargs – a mapping of column + lookup to value, e.g. “age__gt=55”
Return type	返回实力或者一个Does Not Exist异常

这个很是类型thinkphp中的find与findall，get就是只返回一条。

[python] view plaincopy>>> user = User.get(username=username, password=password

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>>> active = User.select().where(active=True)
>>> try:
... user = active.get(username=username, password=password)
... except User.DoesNotExist:
... user = None

classmethod get_or_create(**attributes)

Parameters:	attributes –键值对
Return type:	查询结果实例

返回以键值对做查询条件的结果，如果查询不到，就以该键值对创建一个实例

example:

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>>> CachedObj.get_or_create(key=key, val=some_val)

classmethod
select(query=None)

Return type:	a SelectQuery for the givenModel查询结果

example:

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>>> User.select().where(active=True).order_by('username')

classmethod
update(**query)

Return type:	an UpdateQuery for the givenModel更新

example:

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>>> q = User.update(active=False).where(registration_expired=True)
>>> q.sql()
('UPDATE user SET active=? WHERE registration_expired = ?', [0, 1])
>>> q.execute() # <-- execute it

classmethod
delete(**query)

Return type:	a DeleteQuery for the givenModel删除

example:

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>>> q = User.delete().where(active=False)
>>> q.sql()
('DELETE FROM user WHERE active = ?', [0])
>>> q.execute() # <-- execute it

delelte语句的时候一定要有where语句。

classmethod
insert(**query)

Return type:	an InsertQuery for the givenModel插入

example:

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>>> q = User.insert(username='admin', active=True, registration_expired=False)
>>> q.sql()
('INSERT INTO user (username,active,registration_expired) VALUES (?,?,?)', ['admin', 1, 0])
>>> q.execute()
1

classmethod
raw(sql, *params)

Return type:	a RawQuery for the givenModel使用原始的sql语句

example:

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>>> q = User.raw('select id, username from users')
>>> for user in q:
... print user.id, user.username

classmethod create_table([fail_silently=False])

Parameters:	fail_silently 如果这个值被设置为True，那么该方法就会在创建的时候先检查一个这个表的存在型.

Create the table for the given model.创建表

example:

>>> database.connect()
>>> SomeModel.create_table() # <-- creates the table for SomeModel

classmethoddrop_table([fail_silently=False])

Parameters:	fail_silently –如果是True，在删除之前会检查该表是否存在.

注意，有外键连接的不会受此影响。

classmethod table_exists()

Return type:	返回该数据库是否存在，返回bool值