238376 - container utils should expose a way to get an existing container

Status: RESOLVED INCOMPLETE

(Core Graveyard :: RDF, defect)

Description

[Axel Hecht]

All nsIRDFContainer objects should be retrieved thru container utils.
Right now, you can
a) create a container and Init it (calling Init is something dangerous in
rdf code, so I discourage that)
b) call MakeSeq or any of its friends, which will return a container object
without modifying the datasource at all, if the resource is a container allready.

Neither a) nor b) are really sweet and intuitive, so we should enhance the API
of nsIRDFContainerUtils to return a nsIRDFContainer object for a nsIRDFResource
and a nsIRDFDataSource which already make up a container.

The lack of this api leads to code like in the xultutorial, which is not
very pretty (look at the initSearchList function in findfiles.js)