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from pydantic import BaseModel, EmailStr, ValidationError
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class User(BaseModel):
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    id: int
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    name: str
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    email: EmailStr
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    is_active: bool = True  # 带默认值的可选字段
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# 自动类型转换：age 传入字符串 "25"，会被自动转换为整数 25
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user = User(id=1, name="Alice", email="alice@example.com", is_active=False)
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print(user)
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# 输出: id=1 name='Alice' email='alice@example.com' is_active=False
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# 数据验证失败：会抛出清晰的 ValidationError 异常
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try:
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    invalid_user = User(id="not_an_int", name="Bob", email="bob")
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except ValidationError as e:
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    print(e)

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from pydantic import BaseModel, Field, EmailStr
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class Product(BaseModel):
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    # 字符串长度约束
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    name: str = Field(..., min_length=2, max_length=50, description="产品名称")
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    # 数值范围约束
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    price: float = Field(..., gt=0, le=10000, description="价格必须大于0")
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    # 邮箱格式验证
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    contact_email: EmailStr
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    # 正则表达式约束
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    code: str = Field(..., pattern=r"^P\d{3}$") # 如 P001, P123
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product = Product(
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    name="Laptop",
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    price=999.99,
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    contact_email="test@example.com",
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    code="P001"
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)

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from typing import List
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class Address(BaseModel):
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    city: str
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    street: str
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class Order(BaseModel):
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    order_id: int
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    items: List[Product]  # 嵌套 Product 模型列表
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    address: Address      # 嵌套 Address 模型
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# 可以直接使用字典数据进行实例化
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order_data = {
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    "order_id": 1001,
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    "items": [{"name": "Mouse", "price": 50.0, "contact_email": "a@b.com", "code": "P002"}],
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    "address": {"city": "Shanghai", "street": "Nanjing Road"}
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}
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order = Order(**order_data)
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print(order.address.city)  # 输出: Shanghai

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from pydantic import field_validator
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class UserWithValidator(BaseModel):
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    username: str
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    age: int
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    @field_validator('username')
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    @classmethod
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    def username_no_space(cls, v):
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        if ' ' in v:
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            raise ValueError('用户名不能包含空格')
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        return v
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    @field_validator('age')
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    @classmethod
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    def age_must_be_positive(cls, v):
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        if v <= 0:
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            raise ValueError('年龄必须为正数')
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        return v

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class UserWithConfig(BaseModel):
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    id: int
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    name: str
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    password: str
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    model_config = {
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        "from_attributes": True,  # 允许 model_validate 从任意对象属性创建实例
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        "populate_by_name": True, # 允许通过字段名和别名进行赋值
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    }
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# 假设有一个 ORM 对象
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class ORMUser:
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    def __init__(self, id, name, password):
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        self.id = id
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        self.name = name
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        self.password = password
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orm_user = ORMUser(1, "Charlie", "secret")
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# 可以直接从 ORM 对象创建 Pydantic 模型
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pydantic_user = UserWithConfig.model_validate(orm_user)