[elephant-devel] Test

[Robert L. Read]

This proposed solution is just what I was imagining (only better
described.)
Certainly, whether we use it or not, 0.6.0 should start attaching a
version
to a store.  

On Tue, 2006-03-07 at 14:12 -0500, Ian Eslick wrote:

> Probably we need to add a way to store simple database metadata (list
> structure as a registry with strings, symbols and numbers) that contains
> version and other information.  Upon opening we can look up version
> specific upgrade code if the elephant version is higher than the
> database version and upgrade upon open, prompting the user for a target
> spec if upgrade-by-copy or in-place.  The easiest way to do this is to
> reserve some keywords in the root by using a reserved value such as
> 'elephant::*elephant-metadata*.
> 
> In fact I recommend we agree on a standard for this and ensure that
> 0.6.0 contains this metadata so we can at least recognize 0.6.0+ db's
> when they are opened.  I apologizing if I'm repeating earlier
> discussions.  I've been effectively offline for the past week and a half.
> 
> Proposal:
> 
> (add-to-root 'elephant::*elephant-metadata*
>     '((version 0 6 0)      ;; format (version major minor sub1 ... subN)
>       (spec :bdb "foo")  ;; format (spec <spec as list>)
>       (lisp . :sbcl)))         ;; format (lisp . <lisp-type>)
> 
> In fact we might do the following as well:
> 1) assert an error when add-to-root is used by the user to write
> elephant::*elephant-metadata*
> 2) create a simple interface around add-to-root which provides metadata
> access
> 
> (defmethod get-metadata (tag &optional (sc *store-controller*))
>    (let ((entry (assoc tag (get-from-root *elephant-metadata*)))
>        (when entry
>            (cdr entry))))
> 
> (defmethod set-metadata (tag value &optional (sc *store-controller*))
>    (unless (reserved-metadata-tags tag)
>       ...))
> 
> This way we make sure the user cannot shoot themselves in the foot by
> overwriting reserved
> metadata tags or the reserved root keyword.  Migration should handle the
> reserved keyword
> specially by not migrating reserved tags but migrating any user-defined
> tags.
> 
> This might be overkill as users may only need access to
> system-maintained metadata rather
> than yet another namespace for storing data as the root should function
> equally well...
> 
> Thoughts?
> Ian
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