目錄ORM是什么實(shí)現(xiàn)ORM中的insert功能完善對數(shù)據(jù)類型的檢測抽取到基類中添加數(shù)據(jù)庫驅(qū)動(dòng)執(zhí)行sql語句添加數(shù)據(jù)庫驅(qū)動(dòng)執(zhí)行sql語句測試功能準(zhǔn)備數(shù)據(jù)庫創(chuàng)建模型類測試源代碼ORM是什么

O是 object，也就 類對象 的意思，R是 relation，翻譯成中文是 關(guān)系，也就是關(guān)系數(shù)據(jù)庫中 數(shù)據(jù)表 的意思，M是 mapping，是映射的意思。在ORM框架中，它幫我們把類和數(shù)據(jù)表進(jìn)行了一個(gè)映射，可以讓我們通過類和類對象就能操作它所對應(yīng)的表格中的數(shù)據(jù)。ORM框架還有一個(gè)功能，它可以根據(jù)我們設(shè)計(jì)的類自動(dòng)幫我們生成數(shù)據(jù)庫中的表，省去了我們自己建表的過程。

一個(gè)句話理解就是：創(chuàng)建一個(gè)實(shí)例對象，用創(chuàng)建它的類名當(dāng)做數(shù)據(jù)表名，用創(chuàng)建它的類屬性對應(yīng)數(shù)據(jù)表的字段，當(dāng)對這個(gè)實(shí)例對象操作時(shí)，能夠?qū)?yīng) MySQL 語句。

在 Django 中就內(nèi)嵌了一個(gè) ORM 框架，不需要直接面向數(shù)據(jù)庫編程，而是定義模型類，通過模型類和對象完成數(shù)據(jù)表的增刪改查操作。還有第三方庫 sqlalchemy 都是 ORM框架。

先看看我們大致要實(shí)現(xiàn)什么功能

class User(父類省略): uid = (’uid’, 'int unsigned') name = (’username’, 'varchar(30)') email = (’email’, 'varchar(30)') password = (’password’, 'varchar(30)') ...省略...user = User(uid=123, name=’hui’, email=’[email protected]’, password=’123456’)user.save()# 對應(yīng)如下sql語句# insert into User (uid,username,email,password) values (123,hui,[email protected],123456)

所謂的 ORM 就是讓開發(fā)者在操作數(shù)據(jù)庫的時(shí)候，能夠像操作對象時(shí)通過xxxx.屬性=yyyy一樣簡單，這是開發(fā)ORM的初衷。

實(shí)現(xiàn)ORM中的insert功能

通過 Python 中 元類 簡單實(shí)現(xiàn) ORM 中的 insert 功能

# !/usr/bin/python3# -*- coding: utf-8 -*-# @Author: Hui# @Desc: { 利用Python元類簡單實(shí)現(xiàn)ORM框架的Insert插入功能 }# @Date: 2021/05/17 17:02class ModelMetaclass(type): '''數(shù)據(jù)表模型元類''' def __new__(mcs, cls_name, bases, attrs):print(f’cls_name -> {cls_name}’) # 類名print(f’bases -> {bases}’) # 繼承類print(f’attrs -> {attrs}’) # 類中所有屬性print()# 數(shù)據(jù)表對應(yīng)關(guān)系字典mappings = dict()# 過濾出對應(yīng)數(shù)據(jù)表的字段屬性for k, v in attrs.items(): # 判斷是否是指定的StringField或者IntegerField的實(shí)例對象 # 這里就簡單判斷字段是元組 if isinstance(v, tuple):print(’Found mapping: %s ==> %s’ % (k, v))mappings[k] = v# 刪除這些已經(jīng)在字典中存儲的字段屬性for k in mappings.keys(): attrs.pop(k)# 將之前的uid/name/email/password以及對應(yīng)的對象引用、類名字# 用其他類屬性名稱保存attrs[’__mappings__’] = mappings # 保存屬性和列的映射關(guān)系attrs[’__table__’] = cls_name # 假設(shè)表名和類名一致return type.__new__(mcs, cls_name, bases, attrs)class User(metaclass=ModelMetaclass): '''用戶模型類'''# 類屬性名 表字段 表字段類型 uid = (’uid’, ’int unsigned’) name = (’username’, ’varchar(30)’) email = (’email’, ’varchar(30)’) password = (’password’, ’varchar(30)’) def __init__(self, **kwargs):for name, value in kwargs.items(): setattr(self, name, value) def save(self):fields = []args = []for k, v in self.__mappings__.items(): fields.append(v[0]) args.append(getattr(self, k, None))# 表名table_name = self.__table__# 數(shù)據(jù)表中的字段fields = ’,’.join(fields)# 待插入的數(shù)據(jù)args = ’,’.join([str(i) for i in args])# 生成sql語句sql = f'''insert into {table_name} ({fields}) values ({args})'''print(f’SQL: {sql}’)def main(): user = User(uid=123, name=’hui’, email=’[email protected]’, password=’123456’) user.save()if __name__ == ’__main__’: main()

當(dāng) User 指定元類之后，uid、name、email、password 類屬性將不在類中，而是在 __mappings__ 屬性指定的字典中存儲。 User 類的這些屬性將轉(zhuǎn)變?yōu)槿缦?/p>

__mappings__ = { 'uid': (’uid’, 'int unsigned') 'name': (’username’, 'varchar(30)') 'email': (’email’, 'varchar(30)') 'password': (’password’, 'varchar(30)')}__table__ = 'User'

執(zhí)行的效果如下：

cls_name -> Userbases -> ()attrs -> { ’__module__’: ’__main__’, ’__qualname__’: ’User’, ’__doc__’: ’用戶模型類’, ’uid’: (’uid’, ’int unsigned’), ’name’: (’username’, ’varchar(30)’), ’email’: (’email’, ’varchar(30)’), ’password’: (’password’, ’varchar(30)’), ’__init__’: <function User.__init__ at 0x0000026D520C1048>, ’save’: <function User.save at 0x0000026D520C10D8>}Found mapping: uid ==> (’uid’, ’int unsigned’)Found mapping: name ==> (’username’, ’varchar(30)’)Found mapping: email ==> (’email’, ’varchar(30)’)Found mapping: password ==> (’password’, ’varchar(30)’)SQL: insert into User (uid,username,email,password) values (123,hui,[email protected],123456)完善對數(shù)據(jù)類型的檢測

上面轉(zhuǎn)成的 sql 語句如下：

insert into User (uid,username,email,password) values (12345,hui,[email protected],123456)

發(fā)現(xiàn)沒有，在 sql 語句中字符串類型沒有沒有引號 ’’

正確的 sql 語句應(yīng)該是：

insert into User (uid,username,email,password) values (123, ’hui’, ’[email protected]’, ’123456’)

因此修改 User 類完善數(shù)據(jù)類型的檢測

class ModelMetaclass(type): # 此處和上文一樣, 故省略.... pass class User(metaclass=ModelMetaclass): '''用戶模型類''' uid = (’uid’, 'int unsigned') name = (’username’, 'varchar(30)') email = (’email’, 'varchar(30)') password = (’password’, 'varchar(30)') def __init__(self, **kwargs):for name, value in kwargs.items(): setattr(self, name, value) # 在這里完善數(shù)據(jù)類型檢測 def save(self):fields = []args = []for k, v in self.__mappings__.items(): fields.append(v[0]) args.append(getattr(self, k, None))# 把參數(shù)數(shù)據(jù)類型對應(yīng)數(shù)據(jù)表的字段類型args_temp = list()for temp in args: if isinstance(temp, int):args_temp.append(str(temp)) elif isinstance(temp, str):args_temp.append(f'’{temp}’')# 表名table_name = self.__table__# 數(shù)據(jù)表中的字段fields = ’,’.join(fields)# 待插入的數(shù)據(jù)args = ’,’.join(args_temp)# 生成sql語句sql = f'''insert into {table_name} ({fields}) values ({args})'''print(f’SQL: {sql}’)def main(): user = User(uid=123, name=’hui’, email=’[email protected]’, password=’123456’) user.save()if __name__ == ’__main__’: main()

運(yùn)行效果如下：

cls_name -> Userbases -> ()attrs -> { ’__module__’: ’__main__’, ’__qualname__’: ’User’, ’__doc__’: ’用戶模型類’, ’uid’: (’uid’, ’int unsigned’), ’name’: (’username’, ’varchar(30)’), ’email’: (’email’, ’varchar(30)’), ’password’: (’password’, ’varchar(30)’), ’__init__’: <function User.__init__ at 0x0000026D520C1048>, ’save’: <function User.save at 0x0000026D520C10D8>}Found mapping: uid ==> (’uid’, ’int unsigned’)Found mapping: name ==> (’username’, ’varchar(30)’)Found mapping: email ==> (’email’, ’varchar(30)’)Found mapping: password ==> (’password’, ’varchar(30)’) SQL: insert into User (uid,username,email,password) values(123,’hui’,’[email protected]’,’123456’)抽取到基類中

# !/usr/bin/python3# -*- coding: utf-8 -*-# @Author: Hui# @Desc: { 利用Python元類實(shí)現(xiàn)ORM框架的Insert插入功能 }# @Date: 2021/05/17 17:02class ModelMetaclass(type): '''數(shù)據(jù)表模型元類''' def __new__(mcs, cls_name, bases, attrs):print(f’cls_name -> {cls_name}’) # 類名print(f’bases -> {bases}’) # 繼承類print(f’attrs -> {attrs}’) # 類中所有屬性print()# 數(shù)據(jù)表對應(yīng)關(guān)系字典mappings = dict()# 過濾出對應(yīng)數(shù)據(jù)表的字段屬性for k, v in attrs.items(): # 判斷是否是對應(yīng)數(shù)據(jù)表的字段屬性, 因?yàn)閍ttrs中包含所有的類屬性 # 這里就簡單判斷字段是元組 if isinstance(v, tuple):print(’Found mapping: %s ==> %s’ % (k, v))mappings[k] = v# 刪除這些已經(jīng)在字典中存儲的字段屬性for k in mappings.keys(): attrs.pop(k)# 將之前的uid/name/email/password以及對應(yīng)的對象引用、類名字# 用其他類屬性名稱保存attrs[’__mappings__’] = mappings # 保存屬性和列的映射關(guān)系attrs[’__table__’] = cls_name # 假設(shè)表名和類名一致return type.__new__(mcs, cls_name, bases, attrs)class Model(object, metaclass=ModelMetaclass): '''數(shù)據(jù)表模型基類''' def __init__(self, **kwargs):for name, value in kwargs.items(): setattr(self, name, value) def save(self):fields = []args = []for k, v in self.__mappings__.items(): fields.append(v[0]) args.append(getattr(self, k, None))# 把參數(shù)數(shù)據(jù)類型對應(yīng)數(shù)據(jù)表的字段類型args_temp = list()for temp in args: if isinstance(temp, int):args_temp.append(str(temp)) elif isinstance(temp, str):args_temp.append(f'’{temp}’')# 表名table_name = self.__table__# 數(shù)據(jù)表中的字段fields = ’,’.join(fields)# 待插入的數(shù)據(jù)args = ’,’.join(args_temp)# 生成sql語句sql = f'''insert into {table_name} ({fields}) values ({args})'''print(f’SQL: {sql}’)# 執(zhí)行sql語句# ...class User(Model): '''用戶表模型類''' uid = (’uid’, 'int unsigned') name = (’username’, 'varchar(30)') email = (’email’, 'varchar(30)') password = (’password’, 'varchar(30)')def main(): user = User(uid=123, name=’hui’, email=’[email protected]’, password=’123456’) user.save()if __name__ == ’__main__’: main()添加數(shù)據(jù)庫驅(qū)動(dòng)執(zhí)行sql語句

這里我們使用 pymysql 數(shù)據(jù)庫驅(qū)動(dòng)，來執(zhí)行 sql 語句

在 Model 類中新增一個(gè) get_connection 的靜態(tài)方法用于獲取數(shù)據(jù)庫連接

import pymysqlclass Model(object, metaclass=ModelMetaclass): '''數(shù)據(jù)表模型基類''' def __init__(self, **kwargs):for name, value in kwargs.items(): setattr(self, name, value) @staticmethod def get_connection():'''獲取數(shù)據(jù)庫連接與數(shù)據(jù)游標(biāo):return: conn, cursor'''conn = pymysql.connect( database=’testdb’, host=’localhost’, port=3306, user=’root’, password=’123456’)return conn, conn.cursor() def save(self):fields = []args = []for k, v in self.__mappings__.items(): fields.append(v[0]) args.append(getattr(self, k, None))# 把參數(shù)數(shù)據(jù)類型對應(yīng)數(shù)據(jù)表的字段類型args_temp = list()for temp in args: if isinstance(temp, int):args_temp.append(str(temp)) elif isinstance(temp, str):args_temp.append(f'’{temp}’')# 表名table_name = self.__table__# 數(shù)據(jù)表中的字段fields = ’,’.join(fields)# 待插入的數(shù)據(jù)args = ’,’.join(args_temp)# 生成sql語句sql = f'''insert into {table_name} ({fields}) values ({args})'''print(f’SQL: {sql}’)# 執(zhí)行sql語句conn, cursor = self.get_connection()ret = cursor.execute(sql)print(ret)conn.commit()cursor.close()conn.close()添加數(shù)據(jù)庫驅(qū)動(dòng)執(zhí)行sql語句

這里我們使用 pymysql 數(shù)據(jù)庫驅(qū)動(dòng)，來執(zhí)行 sql 語句

在 Model 類中新增一個(gè) get_connection 的靜態(tài)方法用于獲取數(shù)據(jù)庫連接

import pymysqlclass Model(object, metaclass=ModelMetaclass): '''數(shù)據(jù)表模型基類''' def __init__(self, **kwargs):for name, value in kwargs.items(): setattr(self, name, value) @staticmethod def get_connection():'''獲取數(shù)據(jù)庫連接與數(shù)據(jù)游標(biāo):return: conn, cursor'''conn = pymysql.connect( database=’testdb’, host=’localhost’, port=3306, user=’root’, password=’123456’)return conn, conn.cursor() def save(self):fields = []args = []for k, v in self.__mappings__.items(): fields.append(v[0]) args.append(getattr(self, k, None))# 把參數(shù)數(shù)據(jù)類型對應(yīng)數(shù)據(jù)表的字段類型args_temp = list()for temp in args: if isinstance(temp, int):args_temp.append(str(temp)) elif isinstance(temp, str):args_temp.append(f'’{temp}’')# 表名table_name = self.__table__# 數(shù)據(jù)表中的字段fields = ’,’.join(fields)# 待插入的數(shù)據(jù)args = ’,’.join(args_temp)# 生成sql語句sql = f'''insert into {table_name} ({fields}) values ({args})'''print(f’SQL: {sql}’)# 執(zhí)行sql語句conn, cursor = self.get_connection()ret = cursor.execute(sql)print(ret)conn.commit()cursor.close()conn.close()測試功能準(zhǔn)備數(shù)據(jù)庫

先準(zhǔn)備數(shù)據(jù)庫 testdb 和 user 數(shù)據(jù)表

create database testdb charset=utf8;use testdb;create table user(uid int unsigned auto_increment primary key,username varchar(30) not null,email varchar(30),password varchar(30) not null);

user 表結(jié)構(gòu)如下

+----------+------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+----------+------------------+------+-----+---------+----------------+| uid | int(10) unsigned | NO | PRI | NULL | auto_increment || username | varchar(30) | NO | | NULL ||| email | varchar(30) | YES | | NULL ||| password | varchar(30) | NO | | NULL ||+----------+------------------+------+-----+---------+----------------+創(chuàng)建模型類測試

class User(Model): '''用戶表模型類''' uid = (’uid’, 'int unsigned') name = (’username’, 'varchar(30)') email = (’email’, 'varchar(30)') password = (’password’, 'varchar(30)')def main(): user = User(uid=1, name=’hui’, email=’[email protected]’, password=’123456’) user.save() for i in range(2, 10):user = User( uid=i, name=f’name{i}’, email=f’huidbk@16{i}.com’, password=f’12345{i}’)user.save() if __name__ == ’__main__’: main()

查看數(shù)據(jù)庫 user 表數(shù)據(jù)

mysql> select * from user;+-----+----------+----------------+----------+| uid | username | email | password |+-----+----------+----------------+----------+| 1 | hui | [email protected] | 123456 || 2 | name2 | [email protected] | 123452 || 3 | name3 | [email protected] | 123453 || 4 | name4 | [email protected] | 123454 || 5 | name5 | [email protected] | 123455 || 6 | name6 | [email protected] | 123456 || 7 | name7 | [email protected] | 123457 || 8 | name8 | [email protected] | 123458 || 9 | name9 | [email protected] | 123459 |+-----+----------+----------------+----------+9 rows in set (0.00 sec)源代碼

源代碼已上傳到 Gitee PythonKnowledge: Python知識寶庫，歡迎大家來訪。

以上就是用 Python 元類的特性實(shí)現(xiàn) ORM 框架的詳細(xì)內(nèi)容，更多關(guān)于Python 實(shí)現(xiàn) ORM 框架的資料請關(guān)注好吧啦網(wǎng)其它相關(guān)文章！