Re: [Exist-open] Unique constraints.

[Pierrick B. <pie...@fr...>]

Hi,

Eric Wittmann a écrit :

> Much like you would have in SQL for a unique key or primary key. 
> Another example is Tamino - which allows for the creation of 
> xpath-defined unique constraints in a doctype.

By definition, this is an aplication constraint. I would consider
eXist's triggers to do that, or a highler-level application design.

> In the normal course of operation, our software will not try to
> insert two documents that are the same.  However, recently we found a
> defect during our application crash recovery code, where we had a bug
> that caused a duplicate Alarm document to be inserted.  When running
> against SQL, this bug was obvious (because it failed fast with a
> UNIQUE KEY CONSTRAINT VIOLATION sql error).  When running against
> eXist, there was obviously no error.

Sure. eXist makes no assumption about what you want to insert/upload in
you DB. Just like in a file system....

> So I'm wondering if eXist already has a feature like this, or will I 
> need to add a custom layer within or on top of eXist.

See above. You somehow need to add a "custom" layer. Well, we might
consider "default" (XQuery) triggers to provide an easy (and more 
powerful) way to enforce such constraints...

Cheers,

p.b.