好的：我正在使用Flask-SQLAlchemy和PostgreSQL构建Flask应用程序，我想在我的数据库中创建一个可变的JSON类型列。 SQLAlchemy中有很多关于自定义可变对象类型的在线（以及许多问题）。我找到了这个：sqlalchemy-json（带有完整的写入by the author here），它处理可变的JSON对象类型。从理论上讲，它提供了JsonObject，一种JSON对象类型，具有基本级别的dict和list的更改跟踪，以及NestedJsonObject，一种JSON对象类型，具有针对dict和list的嵌套更改跟踪。它看起来很甜蜜。
我不能为我的生活让它发挥作用，尽管我对它有信心。作为一个注释：上面的作者写的没有显示在列中实现对象类型的示例，所以因为我是一个新手，所以我很有可能让下一个部分出错。然而，我咨询了sqlalchemy.ext.mutable reference，而似乎正确。
这是我的models.py：
from application import app
from flask_sqlalchemy import SQLAlchemy
from flask_login import UserMixin
import sqlalchemy_json # I'm using Alembic for migrations and make this import in my script.py.mako, too, in case that matters
from sqlalchemy_json import NestedJsonObject
db = SQLAlchemy(app)
class User(UserMixin, db.Model): #flask-sqlalchemy provides a Base declaration with db.Model
__tablename__ = 'users'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(80), unique=True)
data = db.Column(NestedJsonObject)
def __init__(self, name, data):
self.name = name
self.data = data
def __repr__(self):
return "<User(id='%d', name='%s', connections='%r')>" % (self.id, self.name, self.data)
...
鉴于此，这是与我的用户合作的一个例子：
data = {}
data['a']= {'b': 'c', 'd': 'e'}
user = User( ... , data)
db.session.add(user)
db.session.commit()
#<User( ... data='{u'a': {u'b': u'c', u'd':u'e'}}')>
初始提交有效。但随后的提交不会：
user = db.session.query(User).filter( ... ).first()
user.data['foo']={}
db.session.commit()
#<User( ... data='{u'a': {u'b': u'c', u'd':u'e'}}')>
user.data['foo']['bar'] = {'x': 'x', 'z': 'z'}
db.session.commit()
#<User( ... data='{u'a': {u'b': u'c', u'd':u'e'}}')>
你明白了。为清楚起见，这里是模块中带有作者符号的两个文件：
请注意文件底部的.associate_with：
# Third-party modules
try:
import simplejson as json
except ImportError:
import json
import sqlalchemy
from sqlalchemy.ext import mutable
# Custom modules
from . import track
class NestedMutable(mutable.MutableDict, track.TrackedDict):
"""SQLAlchemy `mutable` extension dictionary with nested change tracking."""
def __setitem__(self, key, value):
"""Ensure that items set are converted to change-tracking types."""
super(NestedMutable, self).__setitem__(key, self.convert(value, self))
@classmethod
def coerce(cls, key, value):
"""Convert plain dictionary to NestedMutable."""
if isinstance(value, cls):
return value
if isinstance(value, dict):
return cls(value)
return super(cls).coerce(key, value)
class _JsonTypeDecorator(sqlalchemy.TypeDecorator):
"""Enables JSON storage by encoding and decoding on the fly."""
impl = sqlalchemy.String
def process_bind_param(self, value, dialect):
return json.dumps(value)
def process_result_value(self, value, dialect):
return json.loads(value)
class JsonObject(_JsonTypeDecorator):
"""JSON object type for SQLAlchemy with change tracking as base level."""
class NestedJsonObject(_JsonTypeDecorator):
"""JSON object type for SQLAlchemy with nested change tracking."""
mutable.MutableDict.associate_with(JsonObject)
NestedMutable.associate_with(NestedJsonObject)
#!/usr/bin/python
"""This module contains the tracked object classes.
TrackedObject forms the basis for both the TrackedDict and the TrackedList.
A function for automatic conversion of dicts and lists to their tracked
counterparts is also included.
"""
# Standard modules
import itertools
import logging
class TrackedObject(object):
"""A base class for delegated change-tracking."""
_type_mapping = {}
def __init__(self, *args, **kwds):
self.logger = logging.getLogger(type(self).__name__)
self.logger.debug('%s: __init__', self._repr())
self.parent = None
super(TrackedObject, self).__init__(*args, **kwds)
def changed(self, message=None, *args):
"""Marks the object as changed.
If a `parent` attribute is set, the `changed()` method on the parent will
be called, propagating the change notification up the chain.
The message (if provided) will be debug logged.
"""
if message is not None:
self.logger.debug('%s: %s', self._repr(), message % args)
self.logger.debug('%s: changed', self._repr())
if self.parent is not None:
self.parent.changed()
@classmethod
def register(cls, origin_type):
"""Registers the class decorated with this method as a mutation tracker.
The provided `origin_type` is mapped to the decorated class such that
future calls to `convert()` will convert the object of `origin_type` to an
instance of the decorated class.
"""
def decorator(tracked_type):
"""Adds the decorated class to the `_type_mapping` dictionary."""
cls._type_mapping[origin_type] = tracked_type
return tracked_type
return decorator
@classmethod
def convert(cls, obj, parent):
"""Converts objects to registered tracked types
This checks the type of the given object against the registered tracked
types. When a match is found, the given object will be converted to the
tracked type, its parent set to the provided parent, and returned.
If its type does not occur in the registered types mapping, the object
is returned unchanged.
"""
obj_type = type(obj)
for origin_type, replacement in cls._type_mapping.iteritems():
if obj_type is origin_type:
new = replacement(obj)
new.parent = parent
return new
return obj
@classmethod
def convert_iterable(cls, iterable, parent):
"""Returns a generator that performs `convert` on every of its members."""
return (cls.convert(item, parent) for item in iterable)
@classmethod
def convert_iteritems(cls, iteritems, parent):
"""Returns a generator like `convert_iterable` for 2-tuple iterators."""
return ((key, cls.convert(value, parent)) for key, value in iteritems)
@classmethod
def convert_mapping(cls, mapping, parent):
"""Convenience method to track either a dict or a 2-tuple iterator."""
if isinstance(mapping, dict):
return cls.convert_iteritems(mapping.iteritems(), parent)
return cls.convert_iteritems(mapping, parent)
def _repr(self):
"""Simple object representation."""
return '<%(namespace)s.%(type)s object at 0x%(address)0xd>' % {
'namespace': __name__,
'type': type(self).__name__,
'address': id(self)}
@TrackedObject.register(dict)
class TrackedDict(TrackedObject, dict):
"""A TrackedObject implementation of the basic dictionary."""
def __init__(self, source=(), **kwds):
super(TrackedDict, self).__init__(itertools.chain(
self.convert_mapping(source, self),
self.convert_mapping(kwds, self)))
def __setitem__(self, key, value):
self.changed('__setitem__: %r=%r', key, value)
super(TrackedDict, self).__setitem__(key, self.convert(value, self))
def __delitem__(self, key):
self.changed('__delitem__: %r', key)
super(TrackedDict, self).__delitem__(key)
def clear(self):
self.changed('clear')
super(TrackedDict, self).clear()
def pop(self, *key_and_default):
self.changed('pop: %r', key_and_default)
return super(TrackedDict, self).pop(*key_and_default)
def popitem(self):
self.changed('popitem')
return super(TrackedDict, self).popitem()
def update(self, source=(), **kwds):
self.changed('update(%r, %r)', source, kwds)
super(TrackedDict, self).update(itertools.chain(
self.convert_mapping(source, self),
self.convert_mapping(kwds, self)))
@TrackedObject.register(list)
class TrackedList(TrackedObject, list):
"""A TrackedObject implementation of the basic list."""
def __init__(self, iterable=()):
super(TrackedList, self).__init__(self.convert_iterable(iterable, self))
def __setitem__(self, key, value):
self.changed('__setitem__: %r=%r', key, value)
super(TrackedList, self).__setitem__(key, self.convert(value, self))
def __delitem__(self, key):
self.changed('__delitem__: %r', key)
super(TrackedList, self).__delitem__(key)
def append(self, item):
self.changed('append: %r', item)
super(TrackedList, self).append(self.convert(item, self))
def extend(self, iterable):
self.changed('extend: %r', iterable)
super(TrackedList, self).extend(self.convert_iterable(iterable, self))
def remove(self, value):
self.changed('remove: %r', value)
return super(TrackedList, self).remove(value)
def pop(self, index):
self.changed('pop: %d', index)
return super(TrackedList, self).pop(index)
def sort(self, cmp=None, key=None, reverse=False):
self.changed('sort')
super(TrackedList, self).sort(cmp=cmp, key=key, reverse=reverse)
此外，
from .alchemy import NestedJsonObject, NestedMutable, JsonObject
__all__ = (
'NestedJsonObject',
'NestedMutable',
'JsonObject'
)
感谢您阅读此内容。如果您有任何建议，请让我知道。如果这是重复的（我自己找不到一个，但它们可能存在），请将其标记为如此。而且，如果您自己发现上述代码是项目的一个很好的补充，请支持该模块的作者。我不是他/她。这是他/她的许可证：
Copyright (c) 2014, Elmer de Looff <elmer.delooff@gmail.com>
All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
答案 0 :(得分：1)
在查看internnet之后，sqlalchemy-json（感谢edelooff）是最佳选择，但是起源只支持可变dict，this fork更新torotil解决问题，谢谢torotil！
并将记录器放入TrackedObject导致深度复制问题，更好地移动到模块。我分叉了一个新的存储库来解决这个问题：Cysnake4713
另外，我使用origin sqlalchemy.sql.sqltypes.JSON而不是自定义的JsonObject，看起来效果很好。
只需将associate_with部分与：
重新匹配NestedMutable.associate_with(db.JSON)