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  • Python3 对象关系映射(ORM)

    ORM

    • 对象关系映射 Object Relational Mapping
      • 表 ---> 类
      • 字段 ---> 属性
      • 记录 ---> 对象
    # mysql_client.py
    
    import pymysql
    
    
    class MySQLClient:
    
        def __init__(self):
            # 建立连接
            self.client = pymysql.connect(
                host='localhost',
                port=3306,
                user='root',
                password='123',
                database='orm_demo',
                charset='utf8',
                autocommit=True
            )
    
            # 获取游标
            self.cursor = self.client.cursor(
                pymysql.cursors.DictCursor
            )
    
        # 提交查询sql语句并返回结果
        def my_select(self, sql, value=None):
            print('sql:', sql, '
    value:', value)
            self.cursor.execute(sql, value)
            res = self.cursor.fetchall()
            return res
    
        # 提交增加, 修改的sql语句
        def my_execute(self, sql, values):
            try:
                print('<sql>:', sql, '
    <values>:', values)
                self.cursor.execute(sql, values)
            except Exception as e:
                print(e)
    
        # 关闭连接
        def close(self):
            self.cursor.close()
            self.client.close()
    
    
    # ORM.py
    from mysql_client import MySQLClient
    
    # 定义字段类
    class Field:
        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
    
    
    # 定义整数字段类
    class IntegerField(Field):
        def __init__(self, name, column_type='int', primary_key=False, default=0):
            super().__init__(name, column_type, primary_key, default)
    
    
    # 定义字符字段类
    class StringField(Field):
        def __init__(self, name, column_type='varchar(64)', primary_key=False, default=''):
            super().__init__(name, column_type, primary_key, default)
    
    
    # 定义元类
    class OrmMetaClass(type):
        def __new__(cls, class_name, class_bases, class_dict):
    
            if class_name == 'Models':
                return super().__new__(cls, class_name, class_bases, class_dict)
    
            # 没有表名则默认等于类名
            table_name = class_dict.get('table_name', class_name)
    
            primary_key = None
    
            # 定义一个空字典, 用来存放字段对象
            mappings = {}
    
            for key, value in class_dict.items():
                # 筛选字段对象
                if isinstance(value, Field):
                    mappings[key] = value
    
                    if value.primary_key:
                        if primary_key:
                            raise TypeError('只能有一个主键!')
    
                        primary_key = value.name
    
            if not primary_key:
                raise TypeError('必须有一个主键!')
    
            # 删除class_dict中和mappings重复的字段属性
            for key in mappings.keys():
                class_dict.pop(key)
    
            # 将表名添加到class_dict中
            class_dict['table_name'] = table_name
            # 将主键添加到class_dict中
            class_dict['primary_key'] = primary_key
            # 将mappings添加到class_dict中
            class_dict['mappings'] = mappings
    
            return super().__new__(cls, class_name, class_bases, class_dict)
    
    
    # 定义Models类
    class Models(dict, metaclass=OrmMetaClass):
        def __getattr__(self, item):
            return self.get(item)
    
        def __setattr__(self, key, value):
            self[key] = value
    
        # 查询
        @classmethod
        def orm_select(cls, **kwargs):  # kwargs --> {'id': 1}
    
            mysql = MySQLClient()
    
            # select * from User
            if not kwargs:
                sql = 'select * from %s' % cls.table_name
    
                res = mysql.my_select(sql)
    
            else:
                key = list(kwargs.keys())[0]
                value = kwargs.get(key)
    
                sql = 'select * from %s where %s=?' % (cls.table_name, key)
    
                sql = sql.replace('?', '%s')
    
                res = mysql.my_select(sql, value)
                
                mysql.close()
    
                # 返回的是[{}]一个普通的字典(在列表内), 我们把这个字典传入Models类, 让其可以 "对象.属性"
            return [cls(**d) for d in res]  # d是一个字典
    
        # 增加
        def orm_insert(self):
            mysql = MySQLClient()
    
            # 存字段名
            keys = []
            # 存字段值
            values = []
            # 存 "?"
            args = []
    
            for k, v in self.mappings.items():
                # 过滤主键, 因为主键是自增的
                if not v.primary_key:
                    # 字段名
                    keys.append(v.name)
    
                    # 字段值, 没有值则使用默认值
                    values.append(
                        getattr(self, v.name, v.default)
                    )
    
                    # 有几个字段就存放几个"?"
                    args.append('?')
    
            sql = 'insert into %s (%s) values (%s)' % (
                self.table_name,
                ','.join(keys),
                ','.join(args)
            )
    
            sql = sql.replace('?', '%s')
            print(sql)
            print(values)
    
            mysql.my_execute(sql, values)
            mysql.close()
    
        # 修改
        def orm_update(self):
            mysql = MySQLClient()
    
            # 存字段名
            keys = []
            # 存字段值
            values = []
            # 主键值
            primary_key = None
    
            for k, v in self.mappings.items():
                if v.primary_key:
                    # 获取主键值
                    primary_key = v.name + '= %s' % getattr(self, v.name)
    
                else:
                    keys.append(v.name + '=?')
                    values.append(
                        getattr(self, v.name)
                    )
    
            sql = 'update %s set %s where %s' % (
                self.table_name,
                ','.join(keys),
                primary_key
            )
    
            # sql: update table set k1=%s, k2=%s where id=pk
            sql = sql.replace('?', '%s')
    
            mysql.my_execute(sql, values)
            mysql.close()
    
    
    # 定义用户类
    class User(Models):
        user_id = IntegerField('user_id', primary_key=True)
        user_name = StringField('user_name')
        password = StringField('password')
    
    
    user_obj = User.orm_select(user_id=1)[0]  # 查询
    print(user_obj)  # {'user_id': 1, 'user_name': 'blake', 'password': '123'}
    user_obj.user_name = 'bigb'  # 修改user_name
    user_obj.orm_update()  # 将修改提交到数据库
    
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  • 原文地址:https://www.cnblogs.com/bigb/p/11801264.html
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