Hi everyone,
I am currently in work experience ...
The first step of my work was to build a small application using
sqlalchemy.
Association proxy seems to allow to simplify many-to-many
relationships management.
Can i use it to store define a class with an attribute which is a list
of string (or integers ...) ?
Let me explain:
With association proxy, i can do something like:
class Service(Base):
__tablename__ = 'service'
id = Column('s_id', Integer, primary_key=True)
name = Column('s_name', String(63), unique=True)
class NodeService(Base):
__tablename__ = 'node_service'
node_id = Column('n_id', Integer, ForeignKey('node.n_id'),
primary_key=True)
service_id = Column('s_id', Integer, ForeignKey('service.s_id'),
primary_key=True)
service = relationship(Service lazy='joined')
class Node(Base):
__tablename__ = 'node'
id = Column('n_id', Integer, primary_key=True)
node_services = relationship(NodeService, cascade="all, delete-
orphan", lazy='joined')
services = AssociationProxy('nodes_services', 'service', lambda
service: NodeService(service=service))
...
mynode = Node()
mynode.services.append(Service("myservice"))
# instead of
mynode.node_services.append(NodeService(service=Service("myservice")
session.add(mynode)
Is there a way to suppress the Service class in order to handle a list
of string (from python point of view) and have something like:
class NodeAttribute(Base):
__tablename__ = 'node_attribute'
node_id = Column('n_id', Integer, ForeignKey('node.n_id'),
primary_key=True)
attribute = Column('na_id', String, primary_key=True)
class Node(Base):
__tablename__ = 'node'
id = Column('n_id', Integer, primary_key=True)
node_services = relationship(NodeService, cascade="all, delete-
orphan", lazy='joined')
node_attributes = relationship(NodeAttribute cascade="all, delete-
orphan", lazy='joined')
services = AssociationProxy('nodes_services', 'service', lambda
service: NodeService(service=service))
attributes = AssociationProxyLike('node_attributes', ?, ?)
mynode = Node()
mynode.attributes.append("myattribute")
# instead of
mynode.node_attributes.append(NodeAttribute("myattribute"))
# attributes look like a list of string (with append/del functions)
session.add(mynode)
The second step is to replace sqlalchemy+database by something
else ... i will make an other message on the topic
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