Marshmallow 快速文档

本是古典何须时尚 2024-03-27 11:56 63阅读 0赞

#### Marshmallow ####

*  Todo：
 *  正文
 *   *  1. 声明schema
     *  2. 序列化对象 -- dumping
     *   *  2.1 过滤输出 -- only
     *  3. 反序列化 -- load
     *  4. 处理对象集合（多个对象）
     *  5. 必须值 required
     *  5. 声明默认值
     *  6. 只读和只写
     *  7. 自定义key

本文主要对marshmallow的文档进行整理，并记录在学习Marshmallow文档时碰到的一些问题和解决方法  
原文链接：[https://marshmallow.readthedocs.io/en/stable/quickstart.html][https_marshmallow.readthedocs.io_en_stable_quickstart.html]

## Todo： ##

*  添加validation相关的内容
 *  将内容按照接口重新排序
 *  添加ordering, implicit field creation, nested schemas, custom field, extending schemas相关的内容
 *  纠正翻译

## 正文 ##

### 1. 声明schema ###

首先创建一个简单的User类，声明了构造方法和覆写\_\_repr\_\_方法用于打印对象

import datetime as dt
    class User:
        def __init__(self, name, email):
            self.name = name
            self.email = email
            self.created_at = dt.datetime.now()
    
        def __repr__(self):
            return "<User(name={self.name!r})>".format(self=self)

然后创建一个继承Schema的UserSchema类，里面生成name,email,create\_at变量，映射属性名到Field对象

from marshmallow import Schema, fields
    
    class UserSchema(Schema):
        name = fields.Str()
        email = fields.Email()
        created_at = fields.DateTime()

也可以使用Schema.from\_dict()通过传入dict来创建Schema。**比较有用的应用场景是在运行中生成Schema**

UserSchema = Schema.from_dict(
    	{
        
    	    "name": fields.Str(), 
    	    "email": fields.Email(), 
    	    "created_at": fields.DateTime()}
    	)

### 2. 序列化对象 – dumping ###

使用dump、dumps可以序列化对象。dump返回格式化好的数据，dumps返回json String

from pprint import pprint
    
    user = User(name="Monty", email="monty@python.org")
    schema = UserSchema()
    result = schema.dump(user)
    pprint(result)
    # {"name": "Monty",
    #  "email": "monty@python.org",
    #  "created_at": "2014-08-17T14:54:16.049594+00:00"}

#### 2.1 过滤输出 – only ####

使用only，传入tuple或者数组，可以指定输出的fields

summary_schema = UserSchema(only=("name", "email"))
    summary_schema.dump(user)
    # {"name": "Monty", "email": "monty@python.org"}

### 3. 反序列化 – load ###

dump反过来就是load，load会验证并反序列化一个字典 为 应用级别的数据结构。直接使用load，会将dict中的value转换成对应field定义的对象。

from pprint import pprint
    
    user_data = {
        
        "created_at": "2014-08-11T05:26:03.869245",
        "email": "ken@yahoo.com",
        "name": "Ken",
    }
    schema = UserSchema()
    result = schema.load(user_data)
    pprint(result)
    # {'name': 'Ken',
    #  'email': 'ken@yahoo.com',
    #  'created_at': datetime.datetime(2014, 8, 11, 5, 26, 3, 869245)},

如果想将dict整体转换为对象，需要在Schema 中声明一个方法并用@post\_load装饰。下面的例子就是将dict转换成了User对象

from marshmallow import Schema, fields, post_load
    
    class UserSchema(Schema):
        name = fields.Str()
        email = fields.Email()
        created_at = fields.DateTime()
    
        @post_load
        def make_user(self, data, **kwargs):
            return User(**data)
            
    user_data = {
        "name": "Ronnie", "email": "ronnie@stones.com"}
    schema = UserSchema()
    result = schema.load(user_data)
    print(result)  # => <User(name='Ronnie')>

### 4. 处理对象集合（多个对象） ###

在创建Schema的时候，传入（many=True），让Schema可以处理多个对象

user1 = User(name="Mick", email="mick@stones.com")
    user2 = User(name="Keith", email="keith@stones.com")
    users = [user1, user2]
    schema = UserSchema(many=True)
    result = schema.dump(users)  # OR UserSchema().dump(users, many=True)
    pprint(result)
    # [{'name': u'Mick',
    #   'email': u'mick@stones.com',
    #   'created_at': '2014-08-17T14:58:57.600623+00:00'}
    #  {'name': u'Keith',
    #   'email': u'keith@stones.com',
    #   'created_at': '2014-08-17T14:58:57.600623+00:00'}]

### 5. 必须值 required ###

在field中传入required，说明这个值不可或缺。如果缺少值的话，会报错。可以通过 error\_messages=\{“required”: \{“message”: “City required”, “code”: 400\}\} 来自定义错误返回的消息和错误码

from pprint import pprint
    
    from marshmallow import Schema, fields, ValidationError
    
    class UserSchema(Schema):
        name = fields.String(required=True)
        age = fields.Integer(required=True, error_messages={
        "required": "Age is required."})
        city = fields.String(
            required=True,
            error_messages={
        "required": {
        "message": "City required", "code": 400}},
        )
        email = fields.Email()
    
    try:
        result = UserSchema().load({
        "email": "foo@bar.com"})
    except ValidationError as err:
        pprint(err.messages)
        # {'age': ['Age is required.'],
        # 'city': {'code': 400, 'message': 'City required'},
        # 'name': ['Missing data for required field.']}

当一个schema用在不同地方时，required的值不同的话，通过load时传入partial=(“需要忽略的”)，可以忽略required要求的字段值。  
直接传入partial=True可以忽略所有的required

class UserSchema(Schema):
        name = fields.String(required=True)
        age = fields.Integer(required=True)
    
    result = UserSchema().load({
        "age": 42}, partial=("name",)) #跳过name
    # OR UserSchema(partial=('name',)).load({'age': 42}) 
    print(result)  # => {'age': 42}
    
    result = UserSchema().load({
        "age": 42}, partial=True) #跳过所有
    # OR UserSchema(partial=True).load({'age': 42})
    print(result)  # => {'age': 42}

### 5. 声明默认值 ###

通过load\_default和dump\_default，声明默认值

class UserSchema(Schema):
        id = fields.UUID(load_default=uuid.uuid1)
        birthdate = fields.DateTime(dump_default=dt.datetime(2017, 9, 29))
    
    UserSchema().load({
        })
    # {'id': UUID('337d946c-32cd-11e8-b475-0022192ed31b')}
    UserSchema().dump({
        })
    # {'birthdate': '2017-09-29T00:00:00+00:00'}

### 6. 只读和只写 ###

在fields.str()中传入load\_only=True是只写，dump\_only=True是只读

class UserSchema(Schema):
        name = fields.Str()
        # password is "write-only"
        password = fields.Str(load_only=True)
        # created_at is "read-only"
        created_at = fields.DateTime(dump_only=True)

### 7. 自定义key ###

如果输入和输出的变量名不同，需要使用data\_key=""自定义key的名称

class UserSchema(Schema):
        name = fields.String()
        email = fields.Email(data_key="emailAddress")
    
    s = UserSchema()
    
    data = {
        "name": "Mike", "email": "foo@bar.com"}
    result = s.dump(data)
    # {'name': u'Mike',
    # 'emailAddress': 'foo@bar.com'}
    
    data = {
        "name": "Mike", "emailAddress": "foo@bar.com"}
    result = s.load(data)
    # {'name': u'Mike',
    # 'email': 'foo@bar.com'}

[https_marshmallow.readthedocs.io_en_stable_quickstart.html]: https://marshmallow.readthedocs.io/en/stable/quickstart.html