Hi,
first of all, thanks for SQLAlchemy - it's the one project that actually
made me enjoy working with large data collections in applications ;)!
I have an SQLAlchemy model that associates tags (key/value pairs) with
elements, like in attached mwe.py.
Element.tags is a dictionary collection, with some proxying to make it
appear just like a plain dict, which works really well:
session = sessionmaker(bind=engine)()
element = Element()
element.tags = {u"foo": u"bar", u"bang": u"baz"}
session.add(element)
session.commit()
Now, how would I go about getting all Elements that have a certain key/value
pair attached as tag, using session.query(Element)?
I found this documentation
<http://docs.sqlalchemy.org/en/latest/orm/extensions/associationproxy.html#querying-with-association-proxies>
at
http://docs.sqlalchemy.org/en/latest/orm/extensions/associationproxy.html#querying-with-association-proxies
from which I'd derive
session.query(Element).filter(Element.tags.has(key="foo", value="bar")).all().
However, this throws:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/dist-packages/sqlalchemy/ext/associationproxy.py",
line 409, in has
if self._target_is_object:
File "/usr/lib/python2.7/dist-packages/sqlalchemy/util/langhelpers.py", line
754, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File "/usr/lib/python2.7/dist-packages/sqlalchemy/ext/associationproxy.py",
line 244, in _target_is_object
return getattr(self.target_class,
self.value_attr).impl.uses_objectsAttributeError: 'AssociationProxy' object has
no attribute 'impl'
I am using SQLAlchemy 1.0.14 from Debian, in this example with SQLite.
Cheers,
Nik
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from sqlalchemy import create_engine, Column, ForeignKey, Integer, Unicode
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import backref, relationship, sessionmaker
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.orm.collections import attribute_mapped_collection
engine = create_engine("sqlite:///:memory:")
base = declarative_base(bind=engine)
class Tag(base):
__tablename__ = "tags"
tag_id = Column(Integer, primary_key=True)
key = Column(Unicode(256))
value = Column(Unicode(256))
def __init__(self, key="", value="", **kwargs):
self.key = key
self.value = value
base.__init__(self, **kwargs)
class Element(base):
__tablename__ = "elements"
element_id = Column(Integer, primary_key=True)
tags = association_proxy("elements_tags", "tag_value",
creator=lambda k, v: ElementsTags(tag_key=k, tag_value=v))
class ElementsTags(base):
__tablename__ = "elements_tags"
map_id = Column(Integer, primary_key=True)
element_id = Column(Integer, ForeignKey('elements.element_id'))
tag_id = Column(Integer, ForeignKey('tags.tag_id'))
element = relationship(Element, foreign_keys=[element_id],
backref=backref("elements_tags",
collection_class=attribute_mapped_collection("tag_key"),
cascade="all, delete-orphan"))
tag = relationship(Tag, foreign_keys=[tag_id])
tag_key = association_proxy("tag", "key")
tag_value = association_proxy("tag", "value")
base.metadata.create_all()
