[Zope-dev] Acquisition Confusion :S

[Chris Withers]

Evan Simpson wrote:
> I haven't got the whole reason, but here are some of the pieces:
> 
> - never expose a "bare" object, or even one with an incomplete context

Why? You can get at it through aq_base anyway, surely?

Also, Jim Fulton wrote a while back:
> Sure. There is no guarentee that all objects are wrapped.

> - allow the user to backtrack along the context chain

I take it this is the reason for wrappers? Would it matter if the
wrappers were structured differently to provide a different search
order?

> These two together give you the part about aq_parent always being the
> previous acquisition result.

Yup, got that :-)

> - allow recovery of containment information

Urm, didn't quite follow that :S

> - base security on containment

aq_inner, right?

> These two motivate the simplification of raw acquisition.  

Which simplification is that?

> The current acquisition implementation is thus a weird hybrid of containment
> and context.  

I'll say ;-)

> It isn't hard to convert a standard acquisition wrapper into either of the
> other sort.  I'm going to propose adding something like the following
> functions:
> def aq_context(ob):
> def aq_containment(ob):

Okay, so taking our long-running example:

> A /
>   I
>   B/
>     I
>   C/
>     D
> 
> (A contains B and C, C contains D).
> (A contains an I, as does B)
> A.B.C.D

Which I, if any, would each of the following return:

<dtml-var expr="aq_context(A.B.C.D).I">
<dtml-var expr="aq_context(A.B.C).I">
<dtml-var expr="aq_context(A.B).I">
<dtml-var expr="aq_context(A).I">

<dtml-var expr="aq_containment(A.B.C.D).I">
<dtml-var expr="aq_containment(A.B.C).I">
<dtml-var expr="aq_containment(A.B).I">
<dtml-var expr="aq_containment(A).I">

cheers,

Chris