StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>Using the <code>ListView</code>-answer from <a href="https://stackoverflow.com/questions/8984692/how-can-i-change-in-python-the-return-input-type-of-a-list-that-is-implemented-a/" title="Stackoverflow Question 8984692">that</a> question, I came up with the following solution:</p> <p>First, modify <code>Container</code> by adding a <code>ListView</code>-property on top of the SQLAlchemy-property <code>dto_numpy_objects</code>:</p> <pre><code> 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 </code></pre> <p>Second, add method <code>getDTO</code> which can be used as <code>new2raw</code>-<em>converter</em> <code>MyNumpy</code>:</p> <pre><code> def getDTO(self): return self._dto </code></pre> <p>In order to use the <em>backref</em> <code>container_object</code> also from <code>MyNumpy</code> implement it as a wrapper by adding the following method:</p> <pre><code> def __getattr__(self, attr): return getattr(self._dto, attr) </code></pre> <p>All together, the code looks like this:</p> <pre><code>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] </code></pre> <p>For better representation I added</p> <ul> <li><code>DTONumpy.reprInitParams</code></li> <li><code>DTONumpy.__repr__</code></li> <li><code>MyNumpy.__repr__</code></li> </ul> <p>One thing that still doesn't work:</p> <pre><code> c1.my_numpies += [mn1, mn2.dto] </code></pre>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload