[Zope] Which method to generate IDs for objects?

[Tim Hicks]

> Thomas Guettler writes:
>  > On Wed, Jan 16, 2002 at 12:21:45PM -0000, Tim Hicks wrote:
>  > > I don't know if this is very efficient/elegant/etc*, but I use it to
get a
>  > > unique id within a folder...
>  > >
>  > > -------------
>  > > intid = 1
>  > > while 1:
>  > >    if hasattr(photo_folder, str(intid)):
>  > >      intid = intid + 1
>  > >    else:
>  >
>  >
>  > How thread-safe is this? I Java I would write a syncronise block
>  > around i=i+1, because of the following example:
> It is not thread safe and therefore the later "_setObject"
> may raise a BadRequest exception due to duplicate ids.
>
> It is therefore better, to use the "_setObject" directly:
>
>    while 1:
>      try: self._setObject(str(intid),o); break;
>      except BadRequest: intid= intid+1

I follow this, and understand the points you both raise.  Dieter, your
(partial) solution won't work from a PythonScript though because of the _ in
_setObject, right?

>    This, still, is not thread safe. But conflicting threads
>    write the same object. The standard ZODB conflict resolution
>    will normally abort one of the conflicting transactions
>    and restart the corresponding request.

Noted for future reference.

>    I store the "intid" counter in an object attribute, in order
>    not to make so many unsuccessful trials. True, usually,
>    ZODB objects should not be used for counting. But I write
>    the object anyway (for the new object), thus there is no
>    additional penalty to write the counter.

I don't understand why storing the 'intid' in an object attribute cuts down
on the unsuccessful trials.  Do you mean storing it persistently in the
parent object?

tim