Python中编写ORM框架的入门指引

user = User.get('123')

u = db.select_one('select * from users where id=?', '123')
user = User(**u)

from transwarp.orm import Model, StringField, IntegerField

class User(Model):
  __table__ = 'users'
  id = IntegerField(primary_key=True)
  name = StringField()

# 创建实例:
user = User(id=123, name='Michael')
# 存入数据库:
user.insert()

class Model(dict):
  __metaclass__ = ModelMetaclass

  def __init__(self, **kw):
    super(Model, self).__init__(**kw)

  def __getattr__(self, key):
    try:
      return self[key]
    except KeyError:
      raise AttributeError(r"'Dict' object has no attribute '%s'" % key)

  def __setattr__(self, key, value):
    self[key] = value

>>> user['id']
123
>>> user.id
123

class ModelMetaclass(type):
  def __new__(cls, name, bases, attrs):
    mapping = ... # 读取cls的Field字段
    primary_key = ... # 查找primary_key字段
    __table__ = cls.__talbe__ # 读取cls的__table__字段
    # 给cls增加一些字段：
    attrs['__mapping__'] = mapping
    attrs['__primary_key__'] = __primary_key__
    attrs['__table__'] = __table__
    return type.__new__(cls, name, bases, attrs)

class Model(dict):

  ...

  @classmethod
  def get(cls, pk):
    d = db.select_one('select * from %s where %s=?' % (cls.__table__, cls.__primary_key__.name), pk)
    return cls(**d) if d else None

class Model(dict):

  ...

  def insert(self):
    params = {}
    for k, v in self.__mappings__.iteritems():
      params[v.name] = getattr(self, k)
    db.insert(self.__table__, **params)
    return self

user = User(id=123, name='Michael')
user.insert()

  find_first()

  find_all()

  find_by()

 count_all()

 count_by()