通过元类简单实现ORM中的INSERT功能

class ModeMetaclass(type):
    def __new__(cls, name, bases, attrs):
        mappings = dict()
        # 判断是否需要保存
        for k, v in attrs.items():
            # 判断是否是指定的StringField或者IntegerField的实例对象
            if isinstance(v, tuple):
                # print('Found mapping: %s ==> %s' % (k, v))
                mappings[k] = v

        # 删除这些已经在字典中存储的属性
        for k in mappings.keys():
            attrs.pop(k)

        # 将之前的uid\name\email\password以及对应得对象引用、类名字
        attrs['__mappings__'] = mappings  # 保存属性和列的映射关系
        attrs['__table__'] = name  # 假设表名和类名一致
        return type.__new__(cls, name, bases, attrs)


class User(metaclass=ModeMetaclass):
    uid = ('uid', 'int unsigned')
    name = ('name', 'varchar(30)')
    email = ('email', 'varchar(30)')
    password = ('password', 'varchar(30)')
    # 当指定元类之后，以上的类属性将不在类中，而是在__mappings__属性指定的字典中存储
    #__mappings__ = {
    #    'uid':('uid','int unsigned')
    #    'name':('name','varchar(30)')
    #    'email':('email','varchar(30)')
    #    'password':('password','varchar(30)')
    #}
    __table__ = 'User'


    def __init__(self, **kwargs):
        for name, value in kwargs.items():
            setattr(self, name, value)
            # self.name = value

    def save(self):
        fields = []
        args = []
        for k, v in self.__mappings__.items():
            fields.append(v[0])
            args.append(getattr(self, k, None))

        # sql = 'insert into %s (%s) values (%s)' % (self.__table__, ','.join(fields), ','.join([str(i) for i in args]))
        args_temp = list()
        for temp in args:
            # 判断时输入如果是数字类型
            if isinstance(temp, int):
                args_temp.append(str(temp))
            elif isinstance(temp, str):
                args_temp.append("""'%s'""" % temp)

        sql = 'insert into %s (%s) values (%s)' % (self.__table__, ','.join(fields), ','.join(args_temp))
        print('SQL: %s' % sql)


u = User(uid = 12345, name='Michael', email = '[email protected]', password='my-pwd')
# print(u.__dict__)
u.save()