我想在关系数据库中通过SQLAlchemy存储带注释的NumPy数组（如name）。为此，
DTONumpy作为MyNumpy的一部分）将NumPy数组与其数据分开。Container收集NumPy对象。修改Container（从下面的示例中）以一种直接列出MyNumpy对象而不是DTONumpy提供的方式修改import numpy as np
import zlib
import sqlalchemy as sa
from sqlalchemy.orm import relationship, scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.types import TypeDecorator, CHAR
DBSession = scoped_session(sessionmaker())
Base = declarative_base()
#### New SQLAlchemy-Type #####################
class NumpyType (sa.types.TypeDecorator):
impl = sa.types.LargeBinary
def process_bind_param(self, value, dialect):
return zlib.compress(value.dumps(), 9)
def process_result_value(self, value, dialect):
return np.loads(zlib.decompress(value))
##############################################
class DTONumpy(Base):
__tablename__ = 'dtos_numpy'
id = sa.Column(sa.Integer, primary_key=True)
amount = sa.Column('amount', NumpyType)
name = sa.Column('name', sa.String, default='')
container_id = sa.Column(sa.ForeignKey('containers.id'))
container_object = relationship(
"Container",
uselist=False,
backref='dto_numpy_objects'
)
def __init__(self, amount, name=None):
self.amount = np.array(amount)
self.name = name
class Container(Base):
__tablename__ = 'containers'
id = sa.Column(sa.Integer, primary_key=True)
name = sa.Column(sa.String, unique=True)
# HERE: how to access DTONumpy BUT as MyNumpy objects in a way that MyNumpy
# is smoothly integrated into SQLAlchemy?
class MyNumpy(np.ndarray):
_DTO = DTONumpy
def __new__(cls, amount, name=''):
dto = cls._DTO(amount=amount, name=name)
return cls.newByDTO(dto)
@classmethod
def newByDTO(cls, dto):
obj = np.array(dto.amount).view(cls)
obj.setflags(write=False) # Immutable
obj._dto = dto
return obj
@property
def name(self):
return self._dto.name
if __name__ == '__main__':
engine = sa.create_engine('sqlite:///:memory:', echo=True)
DBSession.configure(bind=engine)
Base.metadata.create_all(engine)
session = DBSession()
mn1 = MyNumpy ([1,2,3], "good data")
mn2 = MyNumpy ([2,3,4], "bad data")
# Save MyNumpy objects
c1 = Container()
c1.name = "Test-Container"
c1.dto_numpy_objects += [mn1._dto, mn2._dto] # not a good ui
session.add(c1)
session.commit()
# Load MyNumpy objects
c2 = session.query(Container).filter_by(name="Test-Container").first()
# Ugly UI:
mn3 = MyNumpy.newByDTO(c2.dto_numpy_objects[0])
mn4 = MyNumpy.newByDTO(c2.dto_numpy_objects[1])
name3 = mn3._dto.name
name4 = mn4._dto.name
的好方法和pythonic方法是什么？通过SQLAlchemy？
以下是问题的说明：
Container MyNumpy现在应该提供MyNumpy个对象列表和Container对相应type (c2.my_numpy_objects[0]) == MyNumpy
>>> True
c2.my_numpy_objects.append(MyNumpy ([7,2,5,6], "new data")
print c2.dto_numpy_objects[-1].name
>>> "new data"
对象的引用（列表和引用必须采用SQLAlchemy映射）考虑到）：
{{1}}
答案 0 :(得分：6)
使用ListView - 来自that问题的答案，我提出了以下解决方案：
首先，通过在SQLAlchemy-property Container之上添加ListView - 属性来修改dto_numpy_objects：
def __init__(self, name):
self.name = name
"""
At this point, the following code doesn't work:
---------------------
self.my_numpies = ListView(
self.dto_numpy_objects, # see `DTO_Numpy.container_object`
MyNumpy.newByDTO,
MyNumpy.getDTO)
---------------------
SQLAlchemy seems to change the `dto_numypy_object`-object after the
init-call. Thus, `my_numpies._data` doesn't reference `dto_numpy_objects`
anymore. One solution is to implement a property that initalizes `ListView`
on first access. See below, property `Container.my_numpies`.
"""
@property
def my_numpies(self):
if not hasattr(self, '_my_numpies'):
# The following part can not be exe
self._my_numpies = ListView(
self.dto_numpy_objects, # see `DTO_Numpy.container_object`
MyNumpy.newByDTO,
MyNumpy.getDTO)
return self._my_numpies
其次，添加方法getDTO，可用作new2raw - 转换器 MyNumpy：
def getDTO(self):
return self._dto
为了使用来自container_object的 backref MyNumpy，可以通过添加以下方法将其实现为包装：
def __getattr__(self, attr):
return getattr(self._dto, attr)
总之，代码看起来像这样：
import numpy as np
import zlib
import sqlalchemy as sa
from sqlalchemy.orm import relationship, scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.types import TypeDecorator, CHAR
DBSession = scoped_session(sessionmaker())
Base = declarative_base()
class ListView(list):
def __init__(self, raw_list, raw2new, new2raw):
self._data = raw_list
self.converters = {'raw2new': raw2new,
'new2raw': new2raw}
def __repr__(self):
repr_list = [self.converters['raw2new'](item) for item in self._data]
repr_str = "["
for element in repr_list:
repr_str += element.__repr__() + ",\n "
repr_str = repr_str[:-3] + "]"
return repr_str
def append(self, item):
self._data.append(self.converters['new2raw'](item))
def pop(self, index):
self._data.pop(index)
def __getitem__(self, index):
return self.converters['raw2new'](self._data[index])
def __setitem__(self, key, value):
self._data.__setitem__(key, self.converters['new2raw'](value))
def __delitem__(self, key):
return self._data.__delitem__(key)
def __getslice__(self, i, j):
return ListView(self._data.__getslice__(i,j), **self.converters)
def __contains__(self, item):
return self._data.__contains__(self.converters['new2raw'](item))
def __add__(self, other_list_view):
assert self.converters == other_list_view.converters
return ListView(
self._data + other_list_view._data,
**self.converters)
def __len__(self):
return len(self._data)
def __iter__(self):
return iter([self.converters['raw2new'](item) for item in self._data])
def __eq__(self, other):
return self._data == other._data
#### New SQLAlchemy-Type #####################
class NumpyType (sa.types.TypeDecorator):
impl = sa.types.LargeBinary
def process_bind_param(self, value, dialect):
return zlib.compress(value.dumps(), 9)
def process_result_value(self, value, dialect):
return np.loads(zlib.decompress(value))
##############################################
class DTONumpy(Base):
__tablename__ = 'dtos_numpy'
id = sa.Column(sa.Integer, primary_key=True)
amount = sa.Column('amount', NumpyType)
name = sa.Column('name', sa.String, default='')
container_id = sa.Column(sa.ForeignKey('containers.id'))
container_object = relationship(
"Container",
uselist=False,
backref='dto_numpy_objects'
)
def __init__(self, amount, name=None):
self.amount = np.array(amount)
self.name = name
def reprInitParams(self):
return "(%r, %r)" %(self.amount, self.name)
def __repr__(self):
return "%s%s" %(
self.__class__.__name__,
self.reprInitParams())
class Container(Base):
__tablename__ = 'containers'
id = sa.Column(sa.Integer, primary_key=True)
name = sa.Column(sa.String, unique=True)
def __init__(self, name):
self.name = name
super(Container, self).__init__()
@property
def my_numpies(self):
if not hasattr(self, '_my_numpies'):
# The following part can not be exe
self._my_numpies = ListView(
self.dto_numpy_objects, # see `DTO_Numpy.container_object`
MyNumpy.newByDTO,
MyNumpy.getDTO)
return self._my_numpies
class MyNumpy(np.ndarray):
_DTO = DTONumpy
def __new__(cls, amount, name=''):
dto = cls._DTO(amount=amount, name=name)
return cls.newByDTO(dto)
@classmethod
def newByDTO(cls, dto):
obj = np.array(dto.amount).view(cls)
obj.setflags(write=False) # Immutable
obj._dto = dto
return obj
@property
def name(self):
return self._dto.name
def getDTO(self):
return self._dto
def __getattr__(self, attr):
return getattr(self._dto, attr)
def __repr__(self):
return "%s%s" %(
self.__class__.__name__,
self._dto.reprInitParams())
if __name__ == '__main__':
engine = sa.create_engine('sqlite:///:memory:', echo=True)
DBSession.configure(bind=engine)
Base.metadata.create_all(engine)
session = DBSession()
mn1 = MyNumpy ([1,2,3], "good data")
mn2 = MyNumpy ([2,3,4], "bad data")
# Save MyNumpy-Objects
c1 = Container("Test-Container")
c1.my_numpies.append(mn1)
c1.my_numpies.append(mn2)
session.add(c1)
session.commit()
# Load MyNumpy-Objects
c2 = session.query(Container).filter_by(name="Test-Container").first()
mn3 = c1.my_numpies[0]
mn4 = c1.my_numpies[1]
为了更好的代表性，我添加了
DTONumpy.reprInitParams DTONumpy.__repr__ MyNumpy.__repr__ 有一件事仍然无效：
c1.my_numpies += [mn1, mn2.dto]