ORM + 单例

mysql_singleton.py

import pymysql


class Mysql(object):
    _instance = None
    def __init__(self):
        self.conn = pymysql.connect(
            host = '127.0.0.1',
            port = 3306,
            user = 'root',
            password = '123',
            database = 'db2',
            charset = 'utf8',
            autocommit = True
        )
        self.cursor = self.conn.cursor(pymysql.cursors.DictCursor)

    def close(self):
        self.cursor.close()
        self.conn.close()

    def select(self,sql,args=None):
        self.cursor.execute(sql,args)
        res = self.cursor.fetchall()  # 列表套字典
        return res

    def execute(self,sql,args):
        try:
            self.cursor.execute(sql,args)
        except BaseException as e :
            print(e)

    @classmethod
    def singleton(cls):
        if not cls._instance:
            cls._instance = cls()
        return cls._instance

orm.py

from orm_singleton.mysql_singleton import Mysql


# 定义字段类
class Field(object):
    def __init__(self, name, column_type, primary_key, default):
        self.name = name
        self.column_type = column_type
        self.primary_key = primary_key
        self.default = default


# 定义具体的字段
class StringField(Field):
    def __init__(self, name, column_type='varchar(255)', primary_key=False, default=None):
        super().__init__(name, column_type, primary_key, default)


class IntegerField(Field):
    def __init__(self, name, column_type='int', primary_key=False, default=None):
        super().__init__(name, column_type, primary_key, default)


class ModelMetaClass(type):
    def __new__(cls, class_name, class_bases, class_attrs):
        # 我仅仅只想拦截模型表的类的创建过程
        if class_name == 'Models':
            return type.__new__(cls, class_name, class_bases, class_attrs)
        # 给类放表名,主键字段,所有字段
        table_name = class_attrs.get('table_name', class_name)
        # 定义一个存储主键的变量
        primary_key = None
        # 定义一个字典用来存储用户自定义的表示表的所有字段信息
        mappings = {}
        # for循环当前类的名称空间
        for k, v in class_attrs.items():
            if isinstance(v, Field):
                mappings[k] = v
                if v.primary_key:
                    if primary_key:
                        raise TypeError("主键只能有一个")
                    primary_key = v.name
        # 将重复的键值对删除
        for k in mappings.keys():
            class_attrs.pop(k)
        if not primary_key:
            raise TypeError('必须要有一个主键')
        # 将处理好的数据放入class_attrs中
        class_attrs['table_name'] = table_name
        class_attrs['primary_key'] = primary_key
        class_attrs['mappings'] = mappings
        return type.__new__(cls, class_name, class_bases, class_attrs)


class Models(dict, metaclass=ModelMetaClass):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

    def __getattr__(self, item):
        return self.get(item, '没有该键值对')

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

    # 查询方法
    @classmethod
    def select(cls, **kwargs):
        ms = Mysql.singleton()
        # select * from userinfo
        if not kwargs:
            sql = 'select * from %s' % cls.table_name
            res = ms.select(sql)
        else:
            # select * from userinfo where id = 1
            k = list(kwargs.keys())[0]
            v = kwargs.get(k)
            sql = 'select * from %s where %s=?' % (cls.table_name, k)
            # select * from userinfo where id = ?
            sql = sql.replace('?', '%s')  # select * from userinfo where id = %s
            res = ms.select(sql,v)
        if res:
            return [ cls(**r) for r in res]  # 将数据库的一条数据映射成类的对象

    # 查询单条
    @classmethod
    def select_one(cls, **kwargs):
        # 只查一条
        key = list(kwargs.keys())[0]
        value = kwargs[key]
        # select * from user where id=%s
        sql = 'select * from %s where %s=?' % (cls.table_name, key)
        #
        sql = sql.replace('?', '%s')
        ms = Mysql.singleton()
        re = ms.select(sql, value)
        if re:
            # attrs={'name':'123','password':123}
            # u=User(**attrs)
            # 相当于 User(name='123',password=123)
            u = cls(**re[0])
            return u
        else:
            return

    # 新增方法
    def save(self):
        ms = Mysql.singleton()
        # insert into userinfo(name,password) values('jason','123')
        # insert into %s(%s) values(?)
        fields = []  # [name,password]
        values = []
        args = []
        for k,v in self.mappings.items():
            if not v.primary_key:  # 将id字段去除   因为新增一条数据 id是自动递增的不需要你传
                fields.append(v.name)
                args.append('?')
                values.append(getattr(self,v.name))
        # insert into userinfo(name,password) values(?,?)
        sql = "insert into %s(%s) values(%s)"%(self.table_name,','.join(fields),','.join(args))
        # insert into userinfo(name,password) values(?,?)
        sql = sql.replace('?','%s')
        ms.execute(sql,values)

    # 修改方法:基于已经存在了的数据进行一个修改操作
    def update(self):
        ms = Mysql.singleton()
        # update userinfo set name='jason',password='123' where id = 1
        fields = []  # [name,password]
        values = []
        pr = None
        for k,v in self.mappings.items():
            if v.primary_key:
                pr = getattr(self,v.name,v.default)
            else:
                fields.append(v.name+'=?')
                values.append(getattr(self,v.name,v.default))
        sql = 'update %s set %s where %s = %s'%(self.table_name,','.join(fields),self.primary_key,pr)
        # update userinfo set name='?',password='?' where id = 1
        sql = sql.replace('?','%s')
        ms.execute(sql,values)

#测试
if __name__ == '__main__':
    class Teacher(Models):
        table_name = 'teacher'
        tid = IntegerField(name='tid',primary_key=True)
        tname = StringField(name='tname')
        
    # obj = Teacher(tname='jason老师')
    # obj.save()
    # res = Teacher.select()
    # for r in res:
    #     print(r.tname)
    # print(res)
    
    res = Teacher.select(tid=1)
    teacher_obj = res[0]
    teacher_obj.tname = 'jerry老师'
    teacher_obj.update()

    #-----------------------------------------------------

    class User(Models):
        table_name = 'User'
        id = IntegerField(name='id', primary_key=True)
        name = StringField(name='name')
        password = StringField(name='password')

    print(User.primary_key)
    print(User.mappings)
    obj = User(name='jason')
    print(obj.table_name)
    print(obj.primary_key)
    print(obj.mappings)