sqlalchemy: 'InstrumentedList' object has no attribute 'filter'

Question

I have the following 3 classes:

class Resource:     id = Column(Integer, primary_key=True)     path = Column(Text)     data = Column(Binary)     type = Column(Text)      def set_resource(self, path, data, type):         self.path = path         self.data = data         self.type = type  class EnvironmentResource(Base, Resource):     __tablename__ = 'environment_resources'     parent_id = Column(Integer, ForeignKey('environments.id', ondelete='CASCADE'))     def __init__(self, path, data, type):         self.set_resource(path, data, type)  class Environment(Base):     __tablename__ = 'environments'     id = Column(Integer, primary_key=True)     identifier = Column(Text, unique=True)     name = Column(Text)     description = Column(Text)      _resources = relationship("EnvironmentResource",         cascade="all, delete-orphan",         passive_deletes=True)     _tools = relationship("Tool",         cascade="all, delete-orphan",         passive_deletes=True)      def __init__(self, name, identifier, description):         self.name = name         self.identifier = identifier         self.description = description      def get_resource(self, path):         return self._resources.filter(EnvironmentResource.path==path).first() 

On calling get_resource, I am told that 'InstrumentedList' object has no attribute 'filter' - I've gone through the documentation and can't quite figure this out. What am I missing, so that I may be able to filter the resources corresponding to an environment inside my 'get_resource' method?

PS: I know get_resource will throw an exception, that's what I'd like it to do.

Answer 1

In order to work with the relationship as with Query, you need to configure it with lazy='dynamic'. See more on this in Dynamic Relationship Loaders:

_resources = relationship("EnvironmentResource",     cascade="all, delete-orphan",     lazy='dynamic',     passive_deletes=True)