On Thursday 02 October 2008 17:13:24 rca wrote:
> i think this should be it:
> http://www.sqlalchemy.org/docs/04/plugins.html#plugins_associationp
>roxy
>
> and relevant discussion here:
> http://groups.google.com/group/sqlalchemy/browse_thread/thread/5256
>5295f54fd85/31f53dca1e31e5ee?hl=en&lnk=gst&q=mapper+for+two+tables#3
>1f53dca1e31e5ee
>
> On Oct 2, 3:50 pm, rca <[EMAIL PROTECTED]> wrote:
> > Thanks again, it is much appreciated
> >
> > On Oct 2, 1:03 pm, [EMAIL PROTECTED] wrote:
> > > if the tables have nothing in common, u can have a
> > > MapperExtension that when touching one item updates the proper
> > > table.
> > > as a working big example,
> > > see sqlalachemyAggregator, either
> > > inhttp://dev.gafol.net/t/aggregator
> > > orhttp://dbcook.svn.sourceforge.net/viewvc/dbcook/trunk/dbcook/
> > >misc/agg... which does things like counting summing etc
> > > runtime-updates-of-some-cache.
> > > but i'm not sure if that is what u want; imo u need it more
> > > explicit than this..
> >
> > I have the same feeling (much less assertive here, me, the
> > sql/alchemy noop)
> > but i will study the example
> >
> > > and i still cant see how obj.surface=xyz will lookup and
> > > populate surface_id. imo u need 3 attributes:
> > > - _surface_text - table1.surface, hidden
> > > - _surface_id - table2.surface, hidden
> > > - surface: property which is visible and does the
> > > dispatch/lookup etc
> >
> > yes, the three attributes, i am able to do this now - what I am
> > unable is to map them to different tables -- and be persisted
> > when session.save(obj) -- and
> > session.query(obj).filter(obj.attribute_from_the_second_table)
> > It must be something stupid, i will try to come with an example
hhmm depends if these 2 separate tables are also your objects or just
lookup tables. if they are objetcs, then _surf1 shoud point to that
Obj1/table1 object and change the attribute there; same for _surf2 /
Obj2/table2.
if they're just lookup tables, then i dont know. how u link to which
record to update? give example.
> > > ciao
> > >
> > > On Thursday 02 October 2008 13:59:40 rca wrote:
> > > > thanks for the pointer, I tried and finally managed something
> > > > the synonym (with the big neon "don't panic" in my head)
> > > >
> > > > I can do the conversion and insert "integers id" in place of
> > > > "textual representation" and when accessing the parameter
> > > > .surface, get the textual representation instead of id
> > > > In this way, it works the same as my own type, but just more
> > > > flexible (it can access other parameters of the object).
> > > >
> > > > But still... is there a way to map one class to two tables in
> > > > one go?
> > > >
> > > > To have :
> > > > obj.surface_id --> table1.surface_id
> > > > obj.surface --> table2.surface
> > > >
> > > > when you do:
> > > > obj.surface = "XXX"
> > > > obj.name="YYY"
> > > > to have sqlachemy do:
> > > > "UPDATE table2 SET surface='XXX' WHERE table2.id = 2" (this
> > > > is a foreign key, the value is in the table1.surface_id)
> > > > *AND*
> > > > "UPDATE table1 SET name='YYY' WHERE table1.id = 8"
> > > >
> > > > i am getting this, which is wrong, because surface is foreign
> > > > key, an integer:
> > > > SELECT s1.* FROM table1 AS s1 WHERE s2.surface_id = 'XXX'
> > > >
> > > > if using the custom type, i am able to translate the
> > > > attribute to its id, and use it in the query, yet the synonym
> > > > might be better, only if it was possible to do
> > > > session.query(Object).filter(Object.surface== "XXX")
> > > > and get: SELECT s1.*, s2.* FROM table1 AS s1 LEFT JOIN table2
> > > > AS s2 ON s1.surface_id = s2.id WHERE s2.surface = 'XXX'
> > > >
> > > > remember, my goal was to use obj.surface = "XXX" and have
> > > > this value referenced from the other table.
> > > >
> > > > Sorry if my questions are stupid!
> > > >
> > > > --roman
> > > >
> > > > On Oct 1, 10:21 am, [EMAIL PROTECTED] wrote:
> > > > > maybe try, instead of hiding the conversion inside db-types
> > > > > layer, to move it upper, i.e. make it a real
> > > > > reference/FK-column to real object/table, then make a
> > > > > python property (see "synonim") to do the conversion.
> > > > >
> > > > > On Tuesday 30 September 2008 23:20:16 rca wrote:
> > > > > > Hi all,
> > > > > >
> > > > > > my apologies for a long question, I am new to sqlalchemy
> > > > > > and I was struggling with one problem. I solved it but I
> > > > > > really not sure it's the right way to do it.
> > > > > >
> > > > > > The problem is that I need to create objects like this:
> > > > > > Token(pos=2, surface="helloWorld")
> > > > > >
> > > > > > The surface is string, but in the database, it should be
> > > > > > saved as reference to an other table (looked-up and saved
> > > > > > if not existing)
> > > > > >
> > > > > > The way I solved it was to create my own column type
> > > > > > decorating Integer. On the way in, it gets text and
> > > > > > stores id, on the way out, it gives the text back.
> > > > > >
> > > > > > But I don't know if my solution is safe. For instance,
> > > > > > -- I am decorating Integer type, but on the output there
> > > > > > is string. -- I am using the EntitySingleton recipy, but
> > > > > > I found out I could not use the recommended
> > > > > > Session = scoped_session(sessionmaker())
> > > > > > I had to say: Session = sessionmaker()
> > > > > > -- And I do commit for every new looked-up value
> > > > > >
> > > > > > And also, I have the impression the solution is very
> > > > > > complicated, perhaps you could help me to do it in a
> > > > > > better way.
> > > > > >
> > > > > > Many thanks!
> > > > > >
> > > > > > roman
> > > > > >
> > > > > > Here is the code with an example:
> > > > > > -------------------------------------------------------
> > > > > >
> > > > > > import sqlalchemy as sa
> > > > > > from sqlalchemy.ext.declarative import declarative_base
> > > > > > from sqlalchemy.orm import scoped_session, sessionmaker,
> > > > > > relation, backref, mapper
> > > > > > from sqlalchemy import create_engine, Table, Column,
> > > > > > Integer, String, MetaData, ForeignKey
> > > > > > #from mimetypes import types_map
> > > > > > import weakref
> > > > > > import sqlalchemy.types as types
> > > > > >
> > > > > > Session = sessionmaker() #scoped_session(sessionmaker)
> > > > > >
> > > > > > DBase = declarative_base()
> > > > > >
> > > > > > class MyUnique(types.TypeDecorator):
> > > > > > """a type that decorates Integer,
> > > > > > receives a text representation - eg.
> > > > > > MyValueFromEnumeration and replaces it in the database
> > > > > > with id of the string above It makes sure that inserted
> > > > > > values are unique (creates them if not exist)"""
> > > > > >
> > > > > > impl = types.Integer
> > > > > >
> > > > > > def process_bind_param(self, value, dialect):
> > > > > > #ukladani do databaze
> > > > > > if not hasattr(self, '__unique_valuee'):
> > > > > > self.__unique_valuee = Surface(value)
> > > > > > return self.__unique_valuee.id
> > > > > >
> > > > > > def process_result_value(self, value, dialect):
> > > > > > #vystup
> > > > > > return self.__unique_valuee.surface
> > > > > >
> > > > > > """ #if it is string type
> > > > > > def copy(self):
> > > > > > return MyUniqueString(self.impl.length)
> > > > > > """
> > > > > >
> > > > > > class DocumentBase(object):
> > > > > > def __init__(self):
> > > > > > self.metadata = DBase.metadata
> > > > > > self.engine = None
> > > > > >
> > > > > > def open(self, url='sqlite:///:memory:'):
> > > > > > self.engine = create_engine(url, echo=True)
> > > > > > #engine = create_engine('sqlite:///' + __file__ +
> > > > > > ".db", echo=True)
> > > > > > Session.configure(bind=self.engine)
> > > > > > self.metadata.bind = self.engine
> > > > > >
> > > > > > surface_table = sa.Table('surface',
> > > > > > self.metadata, sa.Column('id', sa.Integer,
> > > > > > primary_key=True, autoincrement=True),
> > > > > > sa.Column('surface', sa.String(500),
> > > > > > autoincrement=True) )
> > > > > >
> > > > > > mapper(Surface, surface_table)
> > > > > >
> > > > > > self.metadata.create_all(checkfirst=True)
> > > > > >
> > > > > > def add(self, document_object):
> > > > > > sess = Session()
> > > > > > sess.save_or_update(document_object)
> > > > > > sess.commit()
> > > > > >
> > > > > > class EntitySingleton(type):
> > > > > > """a metaclass that insures the creation of unique
> > > > > > and non- existent entities for
> > > > > > a particular constructor argument. if an entity with
> > > > > > a particular constructor
> > > > > > argument was already created, either in memory or in
> > > > > > the database, it is returned
> > > > > > in place of constructing the new instance."""
> > > > > >
> > > > > > def __init__(cls, surface, bases, dct):
> > > > > > cls.instances = weakref.WeakValueDictionary()
> > > > > >
> > > > > > def __call__(cls, surface):
> > > > > > session = Session()
> > > > > >
> > > > > > hashkey = surface
> > > > > > try:
> > > > > > return cls.instances[hashkey]
> > > > > > except KeyError:
> > > > > > instance =
> > > > > > session.query(cls).filter(cls.surface==surface).first()
> > > > > > if instance is None:
> > > > > > instance = type.__call__(cls, surface)
> > > > > > #session.begin_nested()
> > > > > > session.add(instance)
> > > > > > session.commit()
> > > > > > # optional - flush the instance when it's
> > > > > > saved session.flush([instance])
> > > > > > cls.instances[hashkey] = instance
> > > > > > return instance
> > > > > >
> > > > > > class Document(DBase):
> > > > > > __tablename__ = 'documents'
> > > > > > id = sa.Column(sa.Integer(9), primary_key=True,
> > > > > > autoincrement=True)
> > > > > > name = sa.Column(sa.String(500))
> > > > > > uri = sa.Column(sa.String(500))
> > > > > > processing_stage = sa.Column(sa.String(500))
> > > > > >
> > > > > > tokens = relation("Token", backref="Document")
> > > > > >
> > > > > > def __xinit__(self, name):
> > > > > > self.name = name
> > > > > > def __repr__(self):
> > > > > > return "<%s('%s','%s')>" % (self.__class__,
> > > > > > self.id, self.name)
> > > > > >
> > > > > > class Token(DBase):
> > > > > > __tablename__ = 'tokens'
> > > > > > id = sa.Column(sa.Integer(6), primary_key=True,
> > > > > > autoincrement=True)
> > > > > > pos = sa.Column(sa.Integer(6))
> > > > > > type = sa.Column(sa.String(500))
> > > > > > surface = sa.Column(MyUnique(500),
> > > > > > sa.ForeignKey('surface.id')) surface_translated =
> > > > > > sa.Column(sa.String(500))
> > > > > > sem = sa.Column(sa.String(500))
> > > > > >
> > > > > > title_id = sa.Column(sa.Integer,
> > > > > > sa.ForeignKey('documents.id')) #document =
> > > > > > relation("Document", backref="Token")
> > > > > >
> > > > > > #def __init__(self, surface=None, **kwargs):
> > > > > >
> > > > > > def __repr__(self):
> >
> > ...
> >
> > read more »
>
>
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