如何使用棉花糖序列化自定义sqlalchemy字段？
如何使用棉花糖序列化自定义sqlalchemy字段？
提问于 2015-10-16 00:40:53
我今天刚刚开始了一个名为flask_wiki的简单项目，我使用了一些烧瓶扩展，如下所示：
- 瓶-SQLAlchemy
- 烧瓶-休息
- MarshMallow
我刚刚发现，MarshMallow项目提供了一个名为“ModelSchema”的类，它从我的SQLAlchemy模型中读取所有字段，并提供一个完全自动化(反)序列化器。
在我的例子中，我创建了一个“GUID”字段，它与RDBM无关，并将其插入到我的Sqlalchemy模型中，如下所示：
from flask.ext.sqlalchemy import SQLAlchemy
from flask_wiki.backend.custom_fields import GUIDField
class Page(db.Model):
"""
Implements the Page Model.
"""
guid = db.Column(GUIDField, primary_key=True, default=uuid.uuid4)
name = db.Column(db.String, nullable=False)
raw_content = db.Column(db.Text)
rendered_content = db.Column(db.Text)
def __repr__(self):
return self.__str__()
def __str__(self):
return self.nameGUIDField是这样实现的：
from sqlalchemy.types import TypeDecorator, CHAR
import uuid
class GUIDField(TypeDecorator):
# Platform independent GUID Implementation that uses little endianess.
impl = CHAR
def load_dialect_impl(self, dialect):
return dialect.type_descriptor(CHAR(32))
def process_bind_param(self, value, dialect):
if value is None:
return value
else:
if isinstance(value, uuid.UUID):
return value.bytes_le
def process_result_value(self, value, dialect):
if value is None:
return value
else:
return uuid.UUID(bytes_le=value)创建测试对象的代码(通过混频器)正在工作；所有and都被正确地生成和验证。
考虑到这一点，刚刚创建了以下MarshMallow序列化器字段：
from marshmallow import fields
import uuid
class GUIDSerializationField(fields.Field):
def _serialize(self, value, attr, obj):
if value is None:
return value
else:
if isinstance(value, uuid.UUID):
return str(value)
else:
return None最后，我创建了SerializerClass：
from flask_wiki.backend.backend import marsh
from flask_wiki.backend.custom_serialization_fields import GUIDSerializationField
from flask_wiki.backend.models import Page
from marshmallow import fields
class PageSchema(marsh.ModelSchema):
class Meta:
model = Page
guid = GUIDSerializationField()
page_schema = PageSchema()
pages_schema = PageSchema(many=True)我尝试在插入guid字段和不插入guid字段时使用最后一段代码，但在所有情况下都会发生以下错误：
Traceback (most recent call last):
File "/home/arthas/dev/flask-wiki/flask_wiki/wiki.py", line 3, in <module>
from flask_wiki.backend import backend
File "/home/arthas/dev/flask-wiki/flask_wiki/backend/__init__.py", line 1, in <module>
import flask_wiki.backend.routes
File "/home/arthas/dev/flask-wiki/flask_wiki/backend/routes.py", line 2, in <module>
from flask_wiki.backend.views import PageView
File "/home/arthas/dev/flask-wiki/flask_wiki/backend/views.py", line 3, in <module>
from flask_wiki.backend.serializers import pages_schema, page_schema
File "/home/arthas/dev/flask-wiki/flask_wiki/backend/serializers.py", line 7, in <module>
class PageSchema(marsh.ModelSchema):
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow/schema.py", line 116, in __new__
dict_cls=dict_cls
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow_sqlalchemy/schema.py", line 53, in get_declared_fields
declared_fields = mcs.get_fields(converter, opts)
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow_sqlalchemy/schema.py", line 77, in get_fields
return converter.fields_for_model(opts.model, fields=opts.fields, exclude=opts.exclude)
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow_sqlalchemy/convert.py", line 75, in fields_for_model
field = self.property2field(prop)
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow_sqlalchemy/convert.py", line 93, in property2field
field_class = self._get_field_class_for_property(prop)
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow_sqlalchemy/convert.py", line 151, in _get_field_class_for_property
field_cls = self._get_field_class_for_column(column)
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow_sqlalchemy/convert.py", line 121, in _get_field_class_for_column
return self._get_field_class_for_data_type(column.type)
File "/home/arthas/env/wiki/lib/python3.5/site-packages/marshmallow_sqlalchemy/convert.py", line 143, in _get_field_class_for_data_type
'Could not find field column of type {0}.'.format(types[0]))
marshmallow_sqlalchemy.exceptions.ModelConversionError: Could not find field column of type <class 'flask_wiki.backend.custom_fields.GUIDField'>.因此，我最后问:如何使用棉花糖序列化自定义sqlalchemy字段？
回答 2
Stack Overflow用户
回答已采纳
发布于 2016-01-18 21:48:26
你需要创建你自己的转换器。试着做这样的事情：
import uuid
from flask_wiki.backend.models import Page
from flask_wiki.backend.backend import marsh
from marshmallow_sqlalchemy.convert import ModelConverter
from flask_wiki.backend.custom_fields import GUIDField
from marshmallow import fields
#Here you are overwriting the list of types of the SQLAlchemy, adding your custom type
class GUIDConverter(ModelConverter):
SQLA_TYPE_MAPPING = dict(
list(ModelConverter.SQLA_TYPE_MAPPING.items()) +
[(GUIDField, fields.Str)]
)
class GUIDSerializationField(fields.Field):
def _serialize(self, value, attr, obj):
if value is None:
return value
else:
if isinstance(value, uuid.UUID):
return str(value)
else:
return None
class PageSchema(marsh.ModelSchema):
class Meta:
model = Page
model_converter = GUIDConverter #Tell to Marshmallow to use your custom converter for this model
guid = GUIDSerializationField(attribute="guid")您还可以看到这链接以获得帮助。我希望它能帮助我，为我糟糕的英语感到遗憾
Stack Overflow用户
发布于 2015-10-16 17:54:17
根据我在文档中看到的内容，您可以在您的model_converter中指定一个元类属性。班级有一个SQLA_TYPE_MAPPING属性，可以在子类中重写，以便将自定义GUID字段添加到自动模式生成器检测到的类型中。
尽管如此，我从来没有用过它，所以我不知道这样做是否有效。
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原文链接：
https://stackoverflow.com/questions/33160762
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