[elephant-devel] Newbee questions

[William Halliburton]

Thank you for the explanation. I was mostly looking to see how to GC the
group. Looks like a future feture.

William

On 3/3/06, Robert L. Read <read at robertlread.net> wrote:
>
> Dear William,
>     Welcome.
>
>     Are you using 0.5 or the latest version from CVS (which has not quite
> been formally released yet)?
> I think this changes slightly based on which version you are using.
>
>     Under the 0.5:
>
>     I think the "Tutorial" on the section Persistent Classes
>
> http://common-lisp.net/project/elephant/doc/Persistent-Classes.html#Persistent-Classes
> shows how to do what you want; I'm pretty sure that it is accurate, but
> haven't actually done it.
> It shows placing the whole object into the root; I honestly would have to
> go back to 0.5 to
> say whether this is really necessary or not.  You can try my code snippet
> below under 0.5
> and see if it works.  (We have been working on what will be 0.6 for quite
> a while.)
>
>     Under the most recent CVS version:
>
>     Yes, each time you make-instance a class with a metaclass of
> :persistent-metaclass, the instance
> is placed in the database with a unique OID.  If you store the OID (for
> example in the root), you
> can can then close the store-controller, exit lisp, restart LISP, reopen
> the store-controller, and
> then either do (make-instance  'my-persistent-class :from-oid OID), or, if
> you have indexed a slot
> of enables class indexing on the class, you could you
> (get-instance-by-class 'my-persistent-class)
>
> ELE-TESTS> (defclass my-persistent-class ()
>         ((slot1 :accessor slot1)
>          (slot2 :accessor slot2))
>         (:metaclass persistent-metaclass))
>
> #<PERSISTENT-METACLASS MY-PERSISTENT-CLASS>
> ELE-TESTS> (setq x (make-instance 'my-persistent-class))
> ; loading system definition from /usr/local/share/lisp/ele-bdb.asd into
> ; #<PACKAGE "ASDF1474">
> ; registering #<SYSTEM ELE-BDB {AA32BE1}> as ELE-BDB
> STYLE-WARNING: implicitly creating new generic function BUILD-BTREE-INDEX
> #<SLEEPYCAT::BDB-STORE-CONTROLLER {B6C1941}>
> ELE-TESTS> (setq x (make-instance 'my-persistent-class))
> #<MY-PERSISTENT-CLASS {B8BA3C1}>
> ELE-TESTS> (elephant::oid x)
> 14700
> ELE-TESTS> (close-store)
> NIL
> ELE-TESTS> (open-store *default-spec*)
> #<SLEEPYCAT::BDB-STORE-CONTROLLER {A97B6B1}>
> ELE-TESTS> (make-instance 'my-persistent-class :from-oid 14700)
> #<MY-PERSISTENT-CLASS {A9FEE69}>
> ELE-TESTS>
>
> In the file classindex.lisp, you can find:
>
> (defgeneric get-instances-by-class (persistent-metaclass))
> (defgeneric get-instances-by-value (persistent-metaclass slot-name value))
> (defgeneric get-instances-by-range (persistent-metaclass slot-name start
> end))
>
> which are very useful for this, and may mean you don't have to store the
> OID in the root if
> you "enable-class-indexing" on the class.
>
>
>
>
>
>
> On Thu, 2006-03-02 at 17:11 -0500, William Halliburton wrote:
>
>
> Starting to use elephant with bdb backend.
>
> Please tell me if the following explanation is correct.
>
> Each time I make-instance a class with a metaclass of
> :persistent-metaclass the class is placed into the database with a unique
> OID. I can retrieve this back with (make-instance 'class :with-oid OID). Now
> this object in not in the root. Must I place it into the root? How do I
> remove old objects?
>
> Thank you,
> William Halliburton
>
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