SQLAlchemy @property使用dump_only在棉花糖中导致“未知字段"错误 [英] SQLAlchemy @property causes 'Unknown Field' error in Marshmallow with dump_only

问题描述

我正在使用flask-marshmallow(marshmallow = v3.0.0rc1，flask-marshmallow = 0.9.0)和flask-sqlalchemy(sqlalchemy = 1.2.16，flask-sqlalchemy = 2.3.2)

I'm using flask-marshmallow (marshmallow=v3.0.0rc1, flask-marshmallow=0.9.0) and flask-sqlalchemy (sqlalchemy=1.2.16, flask-sqlalchemy=2.3.2)

我有这个模型和架构.

from marshmallow import post_load, fields
from .datastore import sqla_database as db
from .extensions import marshmallow as ma

class Study(db.Model):
    _id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String, nullable=False)

    tests = db.relationship("Test", backref="study", lazy='select', cascade="all, delete-orphan")

    @property
    def test_count(self):
        return len(self.tests)

class StudySchema(ma.ModelSchema):
    test_count = fields.Integer(dump_only=True)
    class Meta:
        model = Study
        sqla_session = db.session

schema = StudySchema()
payload = request.get_json()
schema.load(data=payload, instance=Study.query.get(payload["_id"]))
schema.session.commit()

如果我使用此有效负载执行PUT操作 {'_id': 1, 'name': 'Study1', 'test_count': 0}我收到以下异常marshmallow.exceptions.ValidationError: {'test_count': ['Unknown field.']}

If I perform a PUT operation with this payload {'_id': 1, 'name': 'Study1', 'test_count': 0} I get the following exception marshmallow.exceptions.ValidationError: {'test_count': ['Unknown field.']}

如果我删除了dump_only=True，我会得到这个异常AttributeError: can't set attribute，这对我来说很有意义，因为它试图在模型类上设置不带setter方法的test_count.

If I remove the dump_only=True I get this exception AttributeError: can't set attribute which makes sense to me because it's trying to set test_count with no setter method on model class.

我不明白的是为什么dump_only不能忽略该属性.为什么棉花糖在加载过程中仍标记为dump_only时仍尝试验证并理解该字段?

What I do not understand is why is the attribute is not ignored with dump_only. Why is marshmallow still trying to validate and understand this field during load when it's marked as dump_only?

推荐答案

在棉花糖2中，未知或dump_only字段将从输入中忽略.除非用户决定对错误添加自己的验证.

In marshmallow 2, unknown or dump_only fields are ignored from input. Unless the user decides to add his own validation to error on them.

在棉花糖3中，我们将其更改为提供三种可能性(请参见

In marshmallow 3, we changed that to offer three possibilities (see docs):

• RAISE(默认)
• 排除(如棉花糖2)
• INCLUDE(不通过验证即可传递数据)

已经讨论了如何处理dump_only字段，我们得出的结论是，从客户端的角度来看，应该将这些字段视为未知字段(请参阅

There's been discussions about how to deal with dump_only fields and we came to the conclusion that from client perspective, those should be treated just as unknown fields (see https://github.com/marshmallow-code/marshmallow/issues/875).

最重要的是，您的PUT有效负载不应包含dump_only字段.或者，您可以将EXCLUDE策略设置为您的架构，但是我更喜欢前一个选项.

Bottom line, your PUT payload should not include dump_only fields. Or you could set the EXCLUDE policy to your schema, but I'd favor the former option.

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