After some discussion on IRC I did the following: (rebuild 29 '+ArFeLink 'article)
Where 29 is the number of the database file in question and 'article is the relation. It had (+Ref +Link), it now has (+Aux +Ref +Link). So far I haven't noticed any problems. On Wed, Jan 20, 2010 at 8:13 AM, Alexander Burger <a...@software-lab.de>wrote: > Hi Henrik, > > > and it was on IRC so better get it out here. What exactly happens if I > for > > instance add an +Aux relation, will the DB engine recognize that it's new > > and create the index to include all concerned objects, or will it simply > > When the DB model (the "er.l" file) is changed, it is not automatically > detected at runtime. This would be difficult, as it might require a scan > of the whole database. Also, a program is allowed to create arbitrary > data, possibly outside the DB model, so such an automatism would be > dangerous. > > The programmer must understand the implications of a change, and run an > explicit rebuild-script. Adding or changing an index (like adding an > +Aux relation) is one of the most typical cases. > > > > come in to effect on all objects created from now on or will it corrupt > the > > DB? If I recall correctly it will simply work from now on but existing > > objects won't be included in the index. > > Yes. The DB is not really corrupted in such a case, but the affected > objects may not be found at searches. > > > > And if I recall correctly I believe there were also some tools to rebuild > in > > situations like this or? > > 'rebuild' (in "lib/too.l") can be used for that. > > Sometimes, such modifications can be rather complex, and involve changes > in the structures or types of objects. I strongly recommend to test it > first on a local copy of the database. > > It is tricky if not only an index, but the type of indexed data changes. > For example, I had the case last week that the "Land" property of > several object classes changed from a plain string > > (+Ref +String) > > to an entity > > (+Ref +Link) NIL (+Land)) > > Then simply changing the string in all objects to a '+Link' does not > work, because the new index has a different structure. Therefore, > removing the old string must happen in the old model, while setting the > +Link to the land object must happen in the new model. I achieved this > by switching the class of that relation daemon with 'bind' during each > change: > > (for (This ...) # Iterate all involved objects > (let Str (: lnd) # Keep the string value > (bind # Temporarily set old relation classes > (list > (cons (get '+Cls1 'lnd) '(+Need +Sn +Idx +String)) > (cons (get '+Cls2 'lnd) '(+Ref +String)) > ... ) > (put> This 'lnd NIL) ) # Clear old value and index > (put> This 'lnd # Set new (entity) value and build index > (request '(+Land) ... Str ..) ) ) ) > > This is just an example how complex such changes can be. But, on the > other hand, there is almost no limit on what can be done. > > Cheers, > - Alex > -- > UNSUBSCRIBE: mailto:picol...@software-lab.de?subject=unsubscribe >
