orm是什么
o是 object，也就 類對(duì)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(duì)象就能操作它所對(duì)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?cè)O(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(duì)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(duì)應(yīng)數(shù)據(jù)表的字段，當(dāng)對(duì)這個(gè)實(shí)例對(duì)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(duì)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
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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='huidbk@163.com', password='123456')user.save()# 對(duì)應(yīng)如下sql語句# insert into user (uid,username,email,password) values (123,hui,huidbk@163.com,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(duì)象時(shí)通過xxxx.屬性=yyyy一樣簡(jiǎn)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(jiǎn)單實(shí)現(xiàn) orm 中的 insert 功能
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# !/usr/bin/python3# -*- coding: utf-8 -*-# @author: hui# @desc: { 利用python元類簡(jiǎn)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(duì)應(yīng)關(guān)系字典 mappings = dict() # 過濾出對(duì)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(duì)象 # 這里就簡(jiǎn)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(chǔ)的字段屬性 for k in mappings.keys(): attrs.pop(k) # 將之前的uid/name/email/password以及對(duì)應(yīng)的對(duì)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='huidbk@163.com', 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(chǔ)。 user 類的這些屬性將轉(zhuǎn)變?yōu)槿缦?/p>
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__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：
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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,huidbk@163.com,123456) |
完善對(duì)數(shù)據(jù)類型的檢測(cè)
上面轉(zhuǎn)成的 sql 語句如下：
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insert into user (uid,username,email,password) values (12345,hui,huidbk@163.com,123456) |
發(fā)現(xiàn)沒有，在 sql 語句中字符串類型沒有沒有引號(hào) ''
正確的 sql 語句應(yīng)該是：
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insert into user (uid,username,email,password) values (123, 'hui', 'huidbk@163.com', '123456') |
因此修改 user 類完善數(shù)據(jù)類型的檢測(cè)
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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(cè) 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(duì)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='huidbk@163.com', password='123456') user.save()if __name__ == '__main__': main() |
運(yùn)行效果如下：
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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','huidbk@163.com','123456') |
抽取到基類中
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# !/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(duì)應(yīng)關(guān)系字典 mappings = dict() # 過濾出對(duì)應(yīng)數(shù)據(jù)表的字段屬性 for k, v in attrs.items(): # 判斷是否是對(duì)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(jiǎn)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(chǔ)的字段屬性 for k in mappings.keys(): attrs.pop(k) # 將之前的uid/name/email/password以及對(duì)應(yīng)的對(duì)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(duì)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='huidbk@163.com', 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
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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(duì)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
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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(duì)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(cè)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
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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
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+----------+------------------+------+-----+---------+----------------+| 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(cè)試
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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='huidbk@163.com', 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)
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mysql> select * from user;+-----+----------+----------------+----------+| uid | username | email | password |+-----+----------+----------------+----------+| 1 | hui | huidbk@163.com | 123456 || 2 | name2 | huidbk@162.com | 123452 || 3 | name3 | huidbk@163.com | 123453 || 4 | name4 | huidbk@164.com | 123454 || 5 | name5 | huidbk@165.com | 123455 || 6 | name6 | huidbk@166.com | 123456 || 7 | name7 | huidbk@167.com | 123457 || 8 | name8 | huidbk@168.com | 123458 || 9 | name9 | huidbk@169.com | 123459 |+-----+----------+----------------+----------+9 rows in set (0.00 sec) |
源代碼
源代碼已上傳到 gitee pythonknowledge: python知識(shí)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(qǐng)關(guān)注服務(wù)器之家其它相關(guān)文章！
原文鏈接：https://juejin.cn/post/6963443372266618917
