On Sep 14, 2010, at 5:03 PM, A.M. wrote: > Hello, > > I have a schema like this: > > Image > *id > *name > > Metadatakey > *id > *exifkey > *name > > Metadata > *id > *image_id -> Image > *metadatakey_id -> Metadatakey > *value
Thanks to Michael Bayer, I was able to put together the image metadata model I posted on some months ago. I added an association_proxy to make the db schema more transparent which works well when reading (as per this example http://stackoverflow.com/questions/780774/sqlalchemy-dictionary-of-tags), but when setting an attribute through the association proxy, it seems like I would need access to the current session to make the determination of whether or not the metadatakey exists (and grab it). Is it OK practice to use the session in the _metadataCreator method? Is there a better way to accomplish this? The last line of the source code below demonstrates what I wish to accomplish. Thanks. -M ----------------------------------- from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.types import Integer,Unicode from sqlalchemy.orm import relationship,scoped_session,backref from sqlalchemy.orm.session import sessionmaker from sqlalchemy.schema import Column,ForeignKey from sqlalchemy.orm.collections import attribute_mapped_collection from sqlalchemy.engine import create_engine from sqlalchemy.ext.associationproxy import association_proxy Base = declarative_base() class Image(Base): __tablename__ = 'image' id = Column(Integer,primary_key=True) metadatadict = relationship('MetadataValue', collection_class=attribute_mapped_collection('key'), primaryjoin='Image.id==MetadataValue.image_id') def _metadataCreator(key,value): #-----------> get existing MetadataName for this key here, but how? return MetadataValue(namekey=key,value=value) metadatas = association_proxy('metadatadict','value',creator=_metadataCreator) class MetadataName(Base): __tablename__ = 'metadataname' id = Column(Integer,primary_key=True) namekey = Column(Unicode,nullable=False,unique=True) class MetadataValue(Base): __tablename__ = 'metadatavalue' id = Column(Integer,primary_key=True) image_id = Column(Integer,ForeignKey(Image.id),nullable=False) image = relationship(Image, primaryjoin='MetadataValue.image_id==Image.id') metadataname_id = Column(Integer,ForeignKey(MetadataName.id),nullable=False) metadataname = relationship(MetadataName, primaryjoin='MetadataValue.metadataname_id==MetadataName.id') value = Column(Unicode,nullable=False) @property def key(self): return self.metadataname.namekey engine = create_engine('postgresql://localhost/test',echo=True) session = scoped_session(sessionmaker(autocommit=False,bind=engine)) Base.metadata.drop_all(engine) Base.metadata.create_all(engine) metadataname1 = MetadataName(namekey=u'MIMEType') metadataname2 = MetadataName(namekey=u'PixelWidth') img1 = Image() metadatavalue1 = MetadataValue(image=img1,value=u'image/png',metadataname=metadataname1) session.add_all([metadataname1,img1,metadatavalue1,metadataname2]) session.flush() #BEGIN TEST AREA print img1.metadatas['MIMEType'] img1.metadatas['PixelWidth'] = u'300' -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
