On Monday 06 July 2009 16:37:37 Diez B. Roggisch wrote:
> Hi,
>
> I'm faced with a situation where I have
>
> - a 1:n-relationship between Document and DocumentRevision-objects
> - want to delegate most properties of Document to DocumentRevison, which
> means I need an "active" revision.
>
> Modelling that active_revision as "normal" ManyToOne-relationship on the
> document gets me (understandably) into circular-dependency-hell.
>
> Now I know that you can create deferred constraints in some databases
> as "deferrable" which means you can create circular dependencies that must
> only be valid at commit-time, not while inserting.
>
> See e.g.
>
> http://www.network-theory.co.uk/docs/postgresql/vol1/CREATETABLE.html
>
> for PG doing this.
>
> Is there any way to exploit this kind of foreign key reference via elixir,
> or maybe SA itself?
Ok, found it - whyever it skipped my attention at the first look:
active_revision = ManyToOne("DocumentRevision",
use_alter=True,
#constraint_kwargs=dict(deferrable=True,
#initially="deferred")
)
Uncomment the two bottom lines to modify the deferrable-state.
Diez
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