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| class FieldType:
"""字段类型基类"""
def __init__(self, default=None, required=False):
self.default = default
self.required = required
def validate(self, value):
"""验证字段值"""
if value is None and self.required:
raise ValueError("Required field cannot be None")
return self.convert(value) if value is not None else self.default
def convert(self, value):
"""类型转换，子类重写"""
return value
class StringField(FieldType):
"""字符串字段"""
def __init__(self, max_length=None, **kwargs):
super().__init__(**kwargs)
self.max_length = max_length
def convert(self, value):
str_value = str(value)
if self.max_length and len(str_value) > self.max_length:
raise ValueError(f"String too long: {len(str_value)} > {self.max_length}")
return str_value
class IntegerField(FieldType):
"""整数字段"""
def convert(self, value):
try:
return int(value)
except (ValueError, TypeError):
raise ValueError(f"Cannot convert {value} to integer")
class ModelMeta(type):
"""ORM模型的元类"""
def __new__(mcs, name, bases, namespace):
fields = {}
for key, value in list(namespace.items()):
if isinstance(value, FieldType):
fields[key] = value
namespace.pop(key)
for base in bases:
if hasattr(base, '_fields'):
parent_fields = base._fields.copy()
parent_fields.update(fields)
fields = parent_fields
namespace['_fields'] = fields
cls = super().__new__(mcs, name, bases, namespace)
return cls
class Model(metaclass=ModelMeta):
"""ORM模型基类"""
def __init__(self, **kwargs):
self._data = {}
for field_name, field_type in self._fields.items():
value = kwargs.get(field_name)
try:
self._data[field_name] = field_type.validate(value)
except ValueError as e:
raise ValueError(f"Field '{field_name}': {e}")
def __getattr__(self, name):
if name in self._fields:
return self._data.get(name)
raise AttributeError(f"'{self.__class__.__name__}' has no attribute '{name}'")
def __setattr__(self, name, value):
if name.startswith('_'):
super().__setattr__(name, value)
elif name in self._fields:
try:
self._data[name] = self._fields[name].validate(value)
except ValueError as e:
raise ValueError(f"Field '{name}': {e}")
else:
raise AttributeError(f"'{self.__class__.__name__}' has no field '{name}'")
def to_dict(self):
"""转换为字典"""
return self._data.copy()
def __repr__(self):
field_strs = [f"{k}={v!r}" for k, v in self._data.items()]
return f"{self.__class__.__name__}({', '.join(field_strs)})"
class User(Model):
"""用户模型"""
username = StringField(max_length=50, required=True)
email = StringField(required=True)
age = IntegerField(default=0)
bio = StringField(max_length=200)
class Article(Model):
"""文章模型"""
title = StringField(max_length=100, required=True)
content = StringField(required=True)
author_id = IntegerField(required=True)
view_count = IntegerField(default=0)
try:
user = User(username="john_doe", email="john@example.com", age="25")
print(f"创建用户: {user}")
print(f"用户数据: {user.to_dict()}")
user.bio = "Python developer"
print(f"更新后: {user}")
article = Article(
title="Python元类详解",
content="本文深入讲解Python元类机制...",
author_id=1
)
print(f"创建文章: {article}")
print(f"用户年龄类型: {type(user.age)} = {user.age}")
except ValueError as e:
print(f"验证错误: {e}")
try:
invalid_user = User(username="a" * 60, email="")
except ValueError as e:
print(f"创建失败: {e}")
|
