[hibernate-dev] Attribute paths and '.' versus '#' as separator

[Gunnar Morling]

2014-03-29 17:40 GMT+01:00 Steve Ebersole <steve at hibernate.org>:

> To wrap this up..
>
> The most important part for me is being able to identify the point between
> the "attribute base" and the "attribute path".  If we just use a separate
> delimiter there, that's enough for me.  Since one of us has a preference
> for using dots within the "attribute path" part (and its irrelevant to me),
> I'll go with that.  So:
>
> org.h.SomeEntity#nv.to.hell
>

+1 for that.

You might also consider to use "::" as the delimiter between base and path:

    org.h.SomeEntity::nv.to.hell

"::" is the syntax for method references in Java 8 and it may possibly be
used for field references as well in a future Java version. So in some way
it may be nice to resemble that.

--Gunnar


>
>
>
> On Fri, Mar 28, 2014 at 3:18 PM, Steve Ebersole <steve at hibernate.org>
> wrote:
>
> > What we choose as a separator after the "pivot" is irrelevant to a
> degree,
> > especially in terms of the compatibility concern.  I think you understood
> > that, just being clear.  Meaning that calls like:
> >
> > sessionFactoryImplementor.getCollectionPersister(
> "org.h.SomeEntity.nv.to.hell"
> > )
> >
> > will fail whether we use "org.h.SomeEntity#nv.to.hell" or
> "org.h.SomeEntity#nv#to#hell"
> > as the role key.
> >
> > As for "being natural", we'll agree to disagree.  But Java has no such
> > notion as attributes so arguing about what is more natural in how Java
> > represents attribute paths is a bit moot imo.  Were these all *accessible
> > fields*, then sure the code to access them chained would use 'dots'.
>  But I
> > think its pretty plain to see how in the call I listed above:
> >
> > sessionFactoryImplementor.getCollectionPersister(
> "org.h.SomeEntity.nv.to.hell"
> > )
> >
> > the use of '.' locks you into never being able to programatically
> > parse/understand that String structural, which I think is just very
> > limiting in many places.
> >
> >
> >
> > On Fri, Mar 28, 2014 at 1:44 PM, Emmanuel Bernard <
> emmanuel at hibernate.org>wrote:
> >
> >> No strong feeling about it.
> >> It will break the OGM dialects that make use of the collection role
> >> though. So we need to anticipate.
> >>
> >> To me . looks more like the code being used and is a natural notation
> >> even beyond Java. But I get that # offers some additional info.
> >> Have you considered?
> >>
> >>     org.h.SomeEntity#nv.to.hell
> >>
> >> I think that would have my preference actually.
> >>
> >> On 27 Mar 2014, at 23:54, Steve Ebersole <steve at hibernate.org> wrote:
> >>
> >> > This is a bit of a potentially insidious one.  Not the best way to
> start
> >> > off a discussion, I know :)
> >> >
> >> > The premise is this... Until now Hibernate has represented attribute
> >> roles
> >> > using dots.  For an attribute named 'department' on the
> >> com.acme.Employee
> >> > entity, the role would be "com.acme.Employee.department".  In terms of
> >> > embeddables, say Employee had an 'address' embedded with its own
> >> attributes
> >> > like 'city'.  Then, the full role for 'city' would be
> >> > "com.acme.Employee.address.city".
> >> >
> >> > As you can start to see the dots here are completely indistinguishable
> >> in
> >> > terms of those which define the package/class and those which identify
> >> the
> >> > attribute "path".
> >> >
> >> > So one of the things I started playing with in 5 is to replace the
> >> > separators used in attribute paths to use '#', such that
> >> > "com.acme.Employee.address.city" would instead be
> >> > "com.acme.Employee#address#city".  This makes the role fully parseable
> >> > which is actually useful in quite a few situations.  And it REALLY
> >> helps in
> >> > things I have just started working on like storing metadata for
> >> composites
> >> > (embeddeds/embeddables) on the SessionFactory, which is the first step
> >> in
> >> > support for some cool new features around embeddables like
> discriminated
> >> > inheritance support.
> >> >
> >> > However, there is a minor drawback.  Like all attributes, collections
> >> have
> >> > a role.  Unfortunately the use of '.' in their role Strings leaks into
> >> the
> >> > SPI in terms of locating the CollectionPersisters.
> >> >
> >> > So the question is whether to continue with this path of replacing the
> >> use
> >> > of '.' with '#' for attribute path separators.  The drawback is
> >> > unfortunate.  The benefit is very nice, but I can't really say it is
> >> > required atm.
> >> >
> >> > Votes?  Thoughts?
> >> > _______________________________________________
> >> > hibernate-dev mailing list
> >> > hibernate-dev at lists.jboss.org
> >> > https://lists.jboss.org/mailman/listinfo/hibernate-dev
> >>
> >>
> >
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