[bknr-devel] bknr.indices, the slot NIL is missing from the object

[Hans Hübner]

Hi Klaus,

thank you for the manual bug report.  It will be fixed in the upcoming
release of BKNR that is planned for summer.

Your approach to handling the problem looks fine, at least from
superficially looking at it.  I have not looked at cl-prevalence for
quite some time, so I can't say if it will work.

Out of curiosity:  Why are you using cl-prevalence instead of BKNR
datastore?  I am happy to see someone being actually able to use the
indices without the store, but I'm also interested in knowing what our
store is lacking to make you chose another, similar solution.

Thanks,
Hans

P.S.: In fact, we started with cl-prevalence but found it to be too
limited in several aspects. That was why we started writing BKNR
datastore.

2008/2/21, Klaus Unger <UngerKlaus at gmx.de>:
> Hi Hans,
>
>  thanks for the promt response! The code I used was from the datastore-manual
>  page 23. When adding the id slot name I run into the following problem: I use
>  cl-prevalence for serialization. When restoring id-objects I do this
>  without-auto-id, so the objects are created having the id slot unbound and
>  assigned later on. This leads to duplicate entries in the class-index and
>  thus inconsitency. I was not sure what happens if there are multiple objects
>  having a unique-index slot set to Nil.
>
>  Instead of optionaly binding the id parameter in the constructor I now use an
>  initform that at least binds the auto-id or Nil. Is this a good idea?:
>
>  Best regards
>   Klaus
>
>  (defvar *id-counter* 0)
>  (defvar *auto-id* T)
>
>  (defmacro without-auto-id (&body body)
>   `(let ((*auto-id* Nil))
>      , at body))
>
>  (defun next-id ()
>   (when *auto-id*
>       (incf *id-counter*)))
>
>  (defclass id-object ()
>     ((id
>       :reader get-id
>       :initform (next-id)
>       :index-type unique-index
>       :index-initargs (:test #'eql)
>       :index-values find-all-id-objects
>       :index-reader find-object-with-id))
>
>   (:metaclass indexed-class)
>   (:class-indices
>
>     (classes :index-type class-index
>                  :index-initargs (:index-superclasses t)
>                  :slots (id)
>
>                  :index-reader find-all-id-objects-with-class)))
>
>  Am Donnerstag, 21. Februar 2008 07:26:02 schrieb Hans Hübner:
>
> > Hi Klaus,
>  >
>  > the class-index needs to know a slot that it uses for indexing the
>  > objects.  This slot is the unique ID that the index works on.  It must
>  > be added to your base class, but as you can see in the corrected
>  > example below, that should not be much of a problem.
>  >
>  > Note that the :INDICES option in an INDEXED-CLASS either accepts a
>  > predefined index or initargs to create a fresh index.  It is confusing
>  > to mix both initargs and the :INDEX option (which specifies the
>  > preexisting index *CLASS-INDEX* to be used).  I added code to detect
>  > this case.  More error checking would certainly be helpful, so please
>  > report problems when you encounter them and I'll try to make the code
>  > generate better diagnostics.
>  >
>  > Please let us know if you have further questions.
>  >
>  > Hans
>
>