Python Day 45 手撸ORM框架

　　##ORM介绍

#对象关系映射
　　在python中出名的是对象关系映射框架：sqlalchemy
#优势:
        可以让不会mysql的程序员也可以顺顺利利的操做数据库
#缺点:
        可扩展性比较差

#对象关系映射
        类           >>>         数据库的表
        对象         >>>         数据库的表的一条记录
        对象点属性   >>>         记录的某个字段对应的值

#步骤分析
　　一、前言：User(dict)----->User类继承了字典dict------>实例化user=User(name='icon')------>user['name']=owen
　　　　　　　　　　　　　　　　User类中使用__getattr__和__setattr__方法------->能够实现对象点属性：user.name=icon
　　二、__getattr__和__setattr__方法区别:
　　　　__getattr__:当对未定义的属性名称和实例进行点号时,就会用属性名做为字符串调用这个方法。若是继承树能够找到该属性，则不调用此方法
　　　　__setattr__:会拦截全部属性的的赋值语句
　　三、定义Field：数据库中每一列数据，都有：列名，列的数据类型，是不是主键，默认值
　　四、定义Model基类：
　　五、定义ModelMetaclass元类
　　六、单例模式（四五种类型，后续再把该知识点补上）

　　##ORM单例模式

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建立过程
        if class_name == 'Models':
            return type.__new__(cls, class_name, class_bases, class_attrs)
        # 给类放表名,主键字段,全部字段
        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全部字段信息
        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('必需要有一个主键')
        # 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)
    “”“
    # __getattr__:对象获取本身没有的属性或方法的时候自动触发
    # __setattr__:当对象obj.name='jason' 固定句式
    ”“”

    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

    # 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   由于新增一条数据 id是自动递增的不须要你传
                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做
    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)

#测试的话放在main下面，这样看成模块执行时main下面语句不执行
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)

orm

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 # 自动提交
        )
        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

msql_singleton

　　##ORM数据库链接池

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建立过程
        if class_name == 'Models':
            return type.__new__(cls, class_name, class_bases, class_attrs)
        # 给类放表名,主键字段,全部字段
        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全部字段信息
        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('必需要有一个主键')
        # 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()
        # 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

    # 新增方法
    def save(self):
        ms = Mysql()
        # 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   由于新增一条数据 id是自动递增的不须要你传
                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做
    def update(self):
        ms = Mysql()
        # 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)


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 = 'jason老师'
    teacher_obj.update()
    res1 = Teacher.select()
    print(res1)
    # 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)

orm

import pymysql
from orm_pool import db_pool

class Mysql(object):
    def __init__(self):
        self.conn = db_pool.POOL.connection()
        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)

mysql_singleton

from DBUtils.PooledDB import PooledDB
import pymysql

POOL = PooledDB(
    creator=pymysql,  # 使用连接数据库的模块
    maxconnections=6,  # 链接池容许的最大链接数，0和None表示不限制链接数
    mincached=2,  # 初始化时，连接池中至少建立的空闲的连接，0表示不建立
    maxcached=5,  # 连接池中最多闲置的连接，0和None不限制
    maxshared=3,
    # 连接池中最多共享的连接数量，0和None表示所有共享。PS: 无用，由于pymysql和MySQLdb等模块的 threadsafety都为1，全部值不管设置为多少，_maxcached永远为0，因此永远是全部连接都共享。
    blocking=True,  # 链接池中若是没有可用链接后，是否阻塞等待。True，等待；False，不等待而后报错
    maxusage=None,  # 一个连接最多被重复使用的次数，None表示无限制
    setsession=[],  # 开始会话前执行的命令列表。如：["set datestyle to ...", "set time zone ..."]
    ping=0,
    # ping MySQL服务端，检查是否服务可用。# 如：0 = None = never, 1 = default = whenever it is requested, 2 = when a cursor is created, 4 = when a query is executed, 7 = always
    host='127.0.0.1',
    port=3306,
    user='root',
    password='123',
    database='db2',
    charset='utf8',
    autocommit='True'
)

db_pool