44 MySQL & orm对象关系映射

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=‘youku‘,
            charset=‘utf8‘,
            autocommit=True
        )
        self.cursor = self.conn.cursor(pymysql.cursors.DictCursor)

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

    def select(self, sql, args=None):
        self.cursor.execute(sql, args)
        res = self.cursor.fetchall()  # 注意一点:fetchall拿到的数据结构是一个列表套字典[{},{},{}]
        return res

    def execute(self, sql, args):
        # insert into user(name,password) values(‘jason‘,‘123‘)
        # update user set name=‘jason‘,passsword=‘456‘ where id=1
        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

from orm_singleton.mysql_singleton import Mysql  # 导入自定义模块的 mysql


# 表的字段通常需要有的属，字段类性字段名型，是否是主键，默认值
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varchar字段类型
class StringField(Field):
    def __init__(self, name, column_type=‘varchar(255)‘, primary_key=False, default=None):
        super().__init__(name, column_type, primary_key, default)


# 定义int字段类型
class IntegerField(Field):
    def __init__(self, name, column_type=‘int‘, primary_key=False, default=0):
        super().__init__(name, column_type, primary_key, default)


class MyMetaClass(type):
    def __new__(cls, class_name, class_bases, class_attrs):
        # 我们定义的元类是用来拦截模型表的创建过程，而models并不是一张模型表，所以不需要它的创建过程
        if class_name == ‘Models‘:
            return type.__new__(cls, class_name, class_bases, class_attrs)
        table_name = class_attrs.get(‘table_name‘, class_name)
        primary_key = None
        mappings = {}
        # 下面的for循环需要做两件事
        # 1.将单个单个的字段整合成一个
        # 2.确定当前表当地哪个字段是主键
        for k, v in class_attrs.items():  # k:id,name   v:IntegerField(),StringField()
            # 拿出所有自己定义的表的字段属性
            if isinstance(v, Field):
                # 将所有的自己定义的表的字段存入字典中
                mappings[k] = v
                if v.primary_key:
                    # 健壮性校验一张表不能有多个主键
                    if primary_key:
                        raise TypeError("一张表只能有一个主键")
                    primary_key = v.name
        # 循环mapping拿到所有的自定义字段名
        for k in mappings.keys():
            # 将单个单个的字段删除
            class_attrs.pop(k)
        # 校验用户自定义的模型表是否指定了主键字段
        if not primary_key:
            raise TypeError("一张表必须要有主键")
        # 将标示表的特征信息 表名，表的主键字段，表的其他字段都塞到类的名称空间中
        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=MyMetaClass):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

    def __getattr__(self, item):
        return self.get(item, ‘没有该键!‘)

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

    @classmethod
    def select(cls, **kwargs):  # id=1,name=‘jason‘,password=‘123‘
        ms = Mysql.singleton()
        # select * from %s
        if not kwargs:
            sql = "select * from %s" % cls.table_name
            res = ms.select(sql)
        else:
            # select * from %s where %s=%s
            k = list(kwargs.keys())[0]
            v = kwargs.get(k)
            sql = "select * from %s where %s=?" % (cls.table_name, k)  # select * from user where id=?
            sql = sql.replace(‘?‘, ‘%s‘)  # select * from user where id=%s
            res = ms.select(sql, v)
        if res:
            # res = [{},{},{}]
            # cls(name=‘...‘,password=‘...‘)
            return [cls(**r) for r in res]  # [obj1,obj2,obj3]

    def update(self):
        ms = Mysql.singleton()
        # update user set name=‘jason‘,password=‘123‘ where id = 1
        # update user set name=%s,password=%s where id = 1
        # 定义一个列表存储该表的所有字段名
        fields = []
        # 定义一个变量用来存储当前数据对象的主键值
        pr = None
        values = []
        for k, v in self.mappings.items():
            # 先把当前数据对象对应的主键值拿到
            if v.primary_key:
                pr = getattr(self, v.name, v.default)
            else:
                # 除了主键之外的所有字段
                fields.append(v.name + ‘=?‘)  # [name=?,password=?...]
                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 user set name=?,password=? where id=1
        sql = sql.replace(‘?‘, ‘%s‘)
        # update user set name=%s,password=%s where id=1
        ms.execute(sql, values)

    def save(self):
        ms = Mysql.singleton()
        # insert into user(name,password) values(‘jason‘,‘123‘)
        fields = []
        # 专门用来存储与字段对应数量的？
        args = []
        values = []
        for k, v in self.mappings.items():  # name:StringField(name=‘name‘)
            if not v.primary_key:  # 将id字段去除 因为id字段是自增，不需要人为的去操作
                fields.append(v.name)
                args.append(‘?‘)
                values.append(getattr(self, v.name, v.default))
        sql = "insert into %s(%s) values(%s)" % (self.table_name, ‘,‘.join(fields), ‘,‘.join(args))
        # insert into user(name,password) values(?,?)
        sql = sql.replace("?", ‘%s‘)
        # insert into user(name,password) values(%s,%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‘)

from DBUtils.PooledDB import PooledDB
import pymysql

POOL = PooledDB(
    creator=pymysql,  # 使用链接数据库的模块
    maxconnections=6,  # 连接池允许的最大连接数，0和None表示不限制连接数
    mincached=2,  # 初始化时，链接池中至少创建的空闲的链接，0表示不创建
    maxcached=5,  # 链接池中最多闲置的链接，0和None不限制
    maxshared=3,
    # 链接池中最多共享的链接数量，0和None表示全部共享。PS: 无用，因为pymysql和MySQLdb等模块的 threadsafety都为1，所有值无论设置为多少，_maxcached永远为0，所以永远是所有链接都共享。
    blocking=True,  # 连接池中如果没有可用连接后，是否阻塞等待。True，等待；False，不等待然后报错
    maxusage=None,  # 一个链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=‘youku‘,
    charset=‘utf8‘,
    autocommit=True
)

import pymysql
from orm_pool.db_pool import POOL


class Mysql(object):
    def __init__(self):
        self.conn = POOL.connection()
        self.cursor = self.conn.cursor(pymysql.cursors.DictCursor)

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

    def select(self, sql, args=None):
        self.cursor.execute(sql, args)
        res = self.cursor.fetchall()  # 注意一点:fetchall拿到的数据结构是一个列表套字典[{},{},{}]
        return res

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