19321 - implement RDF resource pseudo-aggregation

Status: CLOSED FIXED

(Core Graveyard :: RDF, defect, P1)

Description

[Chris Waterson]

per alecf, scottip, and my discussion, I think we agreed to:

1. Add GetDelegate() and ReleaseDelegate() methods to nsIRDFResource.
GetDelegate() will look kind of like QueryInterface(), but will take a 'const
char*' key, and an IID.

2. Each RDF resource will maintain a table of "delegate" objects, indexed using
a user-defined 'const char*' key.

3. GetDelegate() will search the table for an object with a matching key. If it
finds the object, it will return it, after QI()-ing the object to the specified
IID. If no object is found for the specified key, it will attempt to create an
object using a ProgID that is constructed by combining the key with the
resource's URI's scheme; e.g.

  component://rdf-delegate?key=nscp-mailnews;scheme=imap

It will store the resulting object in the resource's table.

4. Actually, the creation is a bit more involved. The ProgID will be used to
find an XPCOM factory; the factory will be QI()-ed to nsIRDFDelegateFactory,
which has a CreateInstance() method which accepts the full URI of the resource
for which the delegate is being created. This allows the factory to parse the
URI, and create different delegates based on information other than the URI's
scheme.

5. The lifetime of the delegate and the RDF resource will be bound together.
The delegate must forward all AddRef() and Release() calls to the RDF resource.
We'll copy XPCOM's aggregation to get this right.

6. If the delegate wants to "go away" before the RDF resource goes away (e.g.,
mailnews is being unloaded), then the delegate uses the ReleaseDelegate()
method to unbind itself.

Comment 1

[scottputterman]

I'm looking forward to this.  I'm seeing this come up and more and more where we
don't want a mail resource created if we don't have to.

Comment 2

[Alec Flett]

just to add a detail so that putterman isn't confused: the const char* in the
mail case would be something like "msg-folder" or "msg-message" or
"msg-mailfilter" ...basically any object that we'll be reflecting into RDF gets
a msg-<objectname>

Comment 3

[Chris Waterson]

RDF-side stuff is implemented. Now we need to play around with mailnews
resources to get this to work. Somebody open another bug for that.

Comment 4

[Tom Everingham]

development issues - closing based on engineer's comments - please re-open if
necessary