SQLObject

Hi List,

Sorry for the newbie question, but I'm having a hard time finding the right
way to fetch an existing class instance using a different column than id.
Assuming the example Person class with an added "email = StringCol()", I am
able to fetch based on the email using something like:

user = Person.select(Person.q.email=="abc@...", connection=req.conn)[0]

but that seems rather unintuitive compared to Person(10) (or Person.get(10)
now).  I think I'm envisioning an overridden _init  but the magic of the
metaclass is confusing me on how to implement it.  I was also thinking
something along the lines of a class function (ie
user=Person.lookup("abc@...", req.conn) ) would be nice, but since it is
actually being initialized I don't think this is correct.

Any ideas/comments?  Thanks in advance...

-Charles.

On Mar 11, 2004, at 1:19 AM, charles brandt wrote:
> Sorry for the newbie question, but I'm having a hard time finding the 
> right
> way to fetch an existing class instance using a different column than 
> id.
> Assuming the example Person class with an added "email = StringCol()", 
> I am
> able to fetch based on the email using something like:
>
> user = Person.select(Person.q.email=="abc@...", 
> connection=req.conn)[0]
>
> but that seems rather unintuitive compared to Person(10) (or 
> Person.get(10)
> now).  I think I'm envisioning an overridden _init  but the magic of 
> the
> metaclass is confusing me on how to implement it.  I was also thinking
> something along the lines of a class function (ie
> user=Person.lookup("abc@...", req.conn) ) would be nice, but since 
> it is
> actually being initialized I don't think this is correct.
>
> Any ideas/comments?  Thanks in advance...

class Person(SQLObject):
     email = StringCol(alternateID=True)

user = Person.byEmail("abc@...")

Or just:

user = Person.select(email="abc@...]

Or:

class Person(SQLObject):
     def lookup(cls, email, connection=None):
         return cls.select(email=email, connection=connection)[0]
     lookup = classmethod(lookup)

--
Ian Bicking | ianb@... | http://blog.ianbicking.org

Sounds like you might be looking for the alternateID=True argument for columns:

  email = StringCol(alternateID=True)

will add an access method to Person so that:

user = Person.byEmail('abc@...')

will work.

- Luke

Quoting charles brandt <lists@...>:
> user = Person.select(Person.q.email=="abc@...", connection=req.conn)[0]
>
> but that seems rather unintuitive compared to Person(10) (or Person.get(10)
> now).

Thank you Luke and Ian!  alternateID was exactly what I was looking for.  It
always seems so obvious after the fact.  :) Would it make sense to mention
it earlier in the docs when talking about fetching instances that already
exist?  Something like the following maybe?

"You can use the class method .get() to fetch instances that already exist.
So if you wanted to fetch the Person by id 10, you'd call Person.get(10).
To fetch using data from other unique columns, specify alternateID=True in
that column's initialization and use the class method .by<ColumnName>().
(see alternateID for more detail)"

Ian's lookup class example was also what I had in mind. I think there was
one minor typo in the select that I fixed below, incase others try that.
>
> class Person(SQLObject):
>      def lookup(cls, email, connection=None):
>          return cls.select(cls.q.email=email, connection=connection)[0]
>      lookup = classmethod(lookup)
>

I need to read up on new class styles now..  :)  Thanks for the pointers...

-Charles.