一、ORM基本介绍
ORM 是 python编程语言后端web框架 Django的核心思想，“Object Relational Mapping”，即对象-关系映射，简称ORM。
二、实现目标
创建一个实例对象，用创建它的类名当做数据表名，用创建它的类属性对应数据表的字段，当对这个实例对象操作时，能够对应MySQL语句
如图：
三、代码实现
class ModelMetaClass(type):
def __new__(cls, name, bases, attrs):
mappings = dict()
for k, v in attrs.items():
# 只处理类中属性值为元组的键值对
if isinstance(v, tuple):
mappings[k] = v
# 处理完成后删除属性
for k in mappings:
attrs.pop(k)
attrs["__mappings__"] = mappings
attrs["__table__"] = name
# 这里不能用type(name, bases, attrs) 直接返回创建好的类, 不会触发type的__init__方法
return type.__new__(cls, name, bases, attrs)
class Model(metaclass=ModelMetaClass):
# uid = ("uid", "int unsigned")
# name = ("username", "varchar(30)")
# email = ("email", "varchar(30)")
# password = ("password", "varchar(30)")
def __init__(self, **kwargs):
# 将关键字参数添加到实例属性
for k, v in kwargs.items():
setattr(self, k, v)
def save(self):
table_name = self.__table__
field = list()
args = list()
for k, v in self.__mappings__.items():
field.append(v[0])
arg = getattr(self, k, None)
# ["12345","""'Michael'""","""'[email protected]'""","""'my-pwd'"""]
if isinstance(arg, str):
args.append("""'{}'""".format(arg))
else:
args.append(str(arg))
sql = "insert into {}({}) values ({})".format(table_name, ",".join(field), ",".join(args))
print(f"SQL语句: {sql}")
class User(Model):
uid = ("uid", "int unsigned")
name = ("username", "varchar(30)")
email = ("email", "varchar(30)")
password = ("password", "varchar(30)")
u = User(uid=12345, name="Michael", email="[email protected]", password="my-pwd")
u.save()
代码运行结果:
