On Mon, 2007-05-28 at 08:51, Ian Eslick wrote: > A few clarifications: > > Standard persistent classes are not saved by default. To get access
Ian, when are objects that are instanced from persistent classes saved? I simply call (make-instance) on the following class definition: (defclass risk () ((title :accessor title :initarg :title :initform "")) (:metaclass elephant:persistent-metaclass) (:index t)) the resulting object is immediately saved/persisted by Elephant... > to a class via the map-class operator the class or a slot of the > class must be declared as :indexed. If a slot is indexed, then that > value can be used as a key for the object via the get-instances-by- > value interface. Moreover, you can have duplicate slot values and > get-instances-by-value will return all the objects having that slot > value. Understood - this is what I got from the documentation as well. > > Think of the root more like a hash table (single key-value pair) > instead of a set or collection. The simple get-value interface would > be more complex if it could return multiple values. My impression until I saw how persistent objects behave was that everything you want to store via Elephant had to be "rooted". > > It is poor coding practice to use system-assigned OIDs. In future > versions of elephant OIDs may change over time due to GC, auto > recovery of oid space, etc. It's sort of like using the physical > address of an object in a C++ program. There is a legitimate way to > use OIDs outside of elephant, but we haven't yet defined an interface > for users to do so (for example you might want to use OIDs to create > many-to-many maps or efficient persistent sets) Thanks for this insight. Many-to-many maps and sets are exactly what I'm trying to achieve. I found a newly released UUID package for Lisp - http://www.cl-user.net/asp/libs/uuid I'm going to explore using this instead of OIDs. Joubert _______________________________________________ elephant-devel site list elephant-devel@common-lisp.net http://common-lisp.net/mailman/listinfo/elephant-devel
