Python开发个人的ORM框架

谁借莪１个温暖的怀抱￠ 2022-02-27 11:30 251阅读 0赞

Django的ORM框架是在Python创建类对象的原则上，通过继承并重写元类type的属性和方法来实现。根据这一原理，可自主开发ORM框架，我们开发一个类似Django的ORM框架

# 模型字段的基本类
    class Field(object):
        def __init__(self, name, column_type):
            self.name = name
            self.column_type = column_type
        def __str__(self):
            return '<%s:%s>' % (self.__class__.__name__, self.name)
    
    # 模型字段的字符类型
    class StringField(Field):
        def __init__(self, name):
            super().__init__(name, 'varchar(100)')
    
    # 模型字段的整数类型
    class IntegerField(Field):
        def __init__(self, name):
            super().__init__(name, 'bigint')
    
    # 定义元类ModelMetaclass
    class ModelMetaclass(type):
        def __new__(cls, name, bases, attrs):
            mappings = dict()
            for k, v in attrs.items():
                if isinstance(v, Field):
                    print('Found mapping: %s==>%s' % (k, v))
                    mappings[k] = v
            for k in mappings.keys():
                attrs.pop(k)
            attrs['__table__'] = name.lower()
            attrs['__mappings__'] = mappings
            return super().__new__(cls, name, bases, attrs)
    
    # 定义Model类
    class Model(metaclass=ModelMetaclass):
        def __init__(self, *args, **kwargs):
            self.kwargs = kwargs
            super().__init__()
    
        def save(self):
            fields, params = [], []
            for k, v in self.__mappings__.items():
                fields.append(v.name)
                params.append(str(self.kwargs[k]))
            sql = 'insert into %s (%s) values (%s)'
            sql = sql % (self.__table__, ','.join(fields), ','.join(params))
            print('SQL: %s' % sql)
    
    
    # 定义模型User
    class User(Model):
        id = IntegerField('id')
        name = StringField('username')
        email = StringField('email')
        password = StringField('password')
    
    u = User(id=123, name='Dj', email='Dj@dd.gg', password='111')
    u.save()

运行结果如图所示。  
![在这里插入图片描述][20190327155034253.png]  
从图上看到，只要在ORM框架里实现数据库连接，并将SQL语句执行即可数据库操作。

[20190327155034253.png]: /images/20220227/4ebc7a826b744cfbb5cb30b391b8b38e.png