Re: Trying ZODB, background in Relational: mimic auto_increment?

[Jean-Paul Calderone]

On Thu, 14 Aug 2008 05:22:35 -0700 (PDT), Phillip B Oldham <phillip.oldham @gmail.comwrote :

>Hi all. I'm playing with standalone ZODB at the moment trying to get a
>better understanding of its use in applications. I come from a
>PHP/MySQL background, and I'm taking my first steps with Python at the
>same time.
>
>One of the things I'm not understanding about ZODB is assigning
>incremental IDs to objects. For instance, if I were to be writing a
>support-ticket system I'd want to give each ticket a unique number,
>but one that's "human-useable" (otherwise you could just use a UUID -
>try giving one of those over the phone!).
>
>Also, how would one add a new item to the db in this way?
>
>For instance:
>
>class Ticket(Persiste nce):
def __init__(self):
self.id = '' # How do I add a new incremental ID here?
>
># and later on in the app
>
>tkt = Ticket()
>dbroot[?????] = tkt
>
>How would one assign a unique ID to the root at that point?

Here's one way

class Sequence(Persis tence):
def __init__(self):
self.current = 0

def next(self):
self.current += 1
return self.current

ticketSequence = Sequence()

class Ticket(Persiste nce):
def __init__(self):
self.id = ticketSequence. next()

Jean-Paul

[Diez B. Roggisch]

Re: Trying ZODB, background in Relational: mimic auto_increment?

Jean-Paul Calderone wrote:

On Thu, 14 Aug 2008 05:22:35 -0700 (PDT), Phillip B Oldham
<phillip.oldham @gmail.comwrote :

>>Hi all. I'm playing with standalone ZODB at the moment trying to get a
>>better understanding of its use in applications. I come from a
>>PHP/MySQL background, and I'm taking my first steps with Python at the
>>same time.
>>
>>One of the things I'm not understanding about ZODB is assigning
>>incremental IDs to objects. For instance, if I were to be writing a
>>support-ticket system I'd want to give each ticket a unique number,
>>but one that's "human-useable" (otherwise you could just use a UUID -
>>try giving one of those over the phone!).
>>
>>Also, how would one add a new item to the db in this way?
>>
>>For instance:
>>
>>class Ticket(Persiste nce):
> def __init__(self):
> self.id = '' # How do I add a new incremental ID here?
>>
>># and later on in the app
>>
>>tkt = Ticket()
>>dbroot[?????] = tkt
>>
>>How would one assign a unique ID to the root at that point?

>
Here's one way
>
class Sequence(Persis tence):
def __init__(self):
self.current = 0
>
def next(self):
self.current += 1
return self.current
>
ticketSequence = Sequence()
>
class Ticket(Persiste nce):
def __init__(self):
self.id = ticketSequence. next()

Be aware that this isn't working concurrently. Depending on your
application, this can be mitigated using a simple threading.Lock.

Diez

[Thomas Guettler]

Re: Trying ZODB, background in Relational: mimic auto_increment?

auto increment:

Here's one way
>
class Sequence(Persis tence):
def __init__(self):
self.current = 0
>
def next(self):
self.current += 1
return self.current
>
ticketSequence = Sequence()
>
class Ticket(Persiste nce):
def __init__(self):
self.id = ticketSequence. next()
>

I am sorry, but this does not work if several threads or processes
try to get a new id.

Have a look at:

http://www.zope.org/Documentation/Books/ZDG/current/Persistence.stx

"Resolving Conflicts".

BTW, that's one of the points why I switched from ZODB to Postgres.

HTH,
Thomas

--
Thomas Guettler, http://www.thomas-guettler.de/
E-Mail: guettli (*) thomas-guettler + de