Hi, and thanks for quick feedback folks.

Good catch, Jonathan, we recently moved to gitlab since they integrate devops 
and CI build tools. The branch circ_rewrite_master is rebased against master, 
but havent tested properly yet, so its very WIP but you'll get the general idea.


Julian,‚Äč

> I have some concerns about this approach. You are saying that local

> adaptations are reusable for others, but I don't see how. Deichman::*
> will inevitably end up being highly specific. I could probably
> copy/paste some code, but I think we will all have to write our own
> MyLibrary::* stuff.

Your concern is probably sound, since it is easier to add all local adaptations 
to a local namespace (Deichman::*) and be done with it. What I'd suggest though 
is that modules are kept as atomic as possible so that anything can possibly be 
overridden. Its kind of the opposite of todays practise where sysprefs are 
scattered all over the code to adjust for local variations, at least from what 
I've seen in the C4::Circulation. I think it would make sense to allow for a 
Core Circulation that never touch sysprefs, while at the same time having a 
"default" or "full-blown" implementation that can do exactly what 
C4::Circulation does today.

> I'd prefer to extend the capabilities of plugins. This way we could
> combine small generic plugins to answer specific needs.

Actually, I didnt realize plugins was more than tools to extend reports, kind 
of a stepwise db tooling. At least the examples I saw was just CGI templates 
that must be aactively run to modify database. And they seemed based on CGI 
templating which doesnt help us much. In any case, to plug into something 
central, such as Circulation, the circulation modules would need to be 
rewritten.

> But you also say that you reimplemented all the circulation stuff, and
> that it was not complicated, so I'm curious :) Show us the code!


WIP for sure, but as Jonathan found out, here is a single commit on top of 
master

https://gitlab.deichman.no/digibib/Koha/commits/circ_rewrite_master

I see now we use a local caching trick with method attributes (PureFunctions) 
that is not included, so I will have to remove that or it will not work at 
present. But if theres some interest, I will open a bug and commit so people 
can test it. I will try to commit at least to make circulation work as in a 
standard installation.


Benjamin

________________________________
Fra: Brendan Gallagher <i...@bywatersolutions.com>
Sendt: 10. april 2018 21:34
Til: Jonathan Druart
Kopi: Benjamin Rokseth; koha-devel@lists.koha-community.org
Emne: Re: [Koha-devel] Koha Core anyone?

Very excited by this idea.  Lot's to think about.  We're on board with most of 
it and are ready to help.

Cheers,
Brendan

On Tue, Apr 10, 2018 at 9:30 AM, Jonathan Druart 
<jonathan.dru...@bugs.koha-community.org<mailto:jonathan.dru...@bugs.koha-community.org>>
 wrote:
Ha, found it!
https://gitlab.deichman.no/digibib/Koha/commits/circ_rewrite_master
I was looking at the digibib github repo!


On Tue, 10 Apr 2018 at 13:28 Jonathan Druart 
<jonathan.dru...@bugs.koha-community.org<mailto:jonathan.dru...@bugs.koha-community.org>>
 wrote:
Hi Benjamin,

Where is the code of the "working example"?

Cheers,
Jonathan

On Tue, 10 Apr 2018 at 12:04 Benjamin Rokseth 
<benjamin.roks...@deichman.no<mailto:benjamin.roks...@deichman.no>> wrote:
Community hackers,

on hackfest I got introvertly enthusiastic about the concept of a Koha Core, and
about time I shared some thoughts.

Background: Deichman (Oslo Public Library) is heavily leaning on bleeding edge 
Koha
development (REST, Objects, Auth, NCIP and such) and, like at least some 
others, maintain
a lot of local patches to tweak Koha into our users needs. Some are probably 
interesting to
Community, others not. Now to keep everything in sync with Community would be 
amazing,
but not likely to happen anytime soon.

Great work has been done on refactoring Koha (new namespace, Koha Objects and 
REST api, etc.),
but we'd like to suggest one more - a Koha core.
The idea is simple: borrow from object oriented languages, java, or actually 
more ruby, since
we're dealing with a dynamic language, use class/module inheritance and method 
overrides.
Perl has the "use parent" concept which simplifies inheritance/subclassing and 
allows for
nested overrides.

As an example we refactored the current circulation in Koha, since this for us 
is the core
functionality that we depend on and need to hook our local quirks on top of.
An attempt to illustrate:

+------------+
| Core::Main |
+--^---------+
   |
+--+----------------+
| Core::Prefs       |
| Core::Exceptions  |                +-----------------------+
| Core::Circulation <-----+------+---| Deichman::Circulation |
| ...               |     |      |   +---^-------------------+
+-------------------+     |      |       |
                          |      |       |
       +------------------+------+       +--------------------------+
       | Core::Circulation::SIP  |       |Deichman::Circulation::SIP|
       +------------------------------------------------------------+
                                 |        use parent qw(
                                 |          Deichman::Circulation
          +----------------------+          Core::Circulation::SIP
          | Core::Circulation::UI|        )
          +----------------------+
                                 |
                                 ~

* Core::Main is simply an empty class that act as a parent for any child, 
including Core::Circulation.
* Core::Circulation has a constructor that takes koha objects item and library, 
optionally patron
  and sysprefs overrides. It can have accessors such as checkout, messages and 
other things needed for
  intra, SIP or whatever. It has methods Checkin, Checkout and Renew, amongst 
others.
* then: Deichman::Circulation::SIP in this example is a local override that 
inherits from parents
  Deichman::Circulation and Core::Circulation::SIP

now the beauty of this is that Deichman::Circulation::SIP can override anything 
(even the constructor)
without touching any of the core code, and perl will traverse the inheritance 
tree until it finds the
first matching constructor and method.

Pros:
  - simpler, more readable and more reusable code.
  - local adaptations are easy to hande, and reusable for others
  - the slight overhead of using blessed objects and inheritance is easily 
gained by the fact that any
    operation will only need fetching Koha objects once (item,library,patron 
etc) instead of refetching
    them numerous times spread across methods calls and loops
  - way less db calls if done right, faster Koha
  - no more C4::Context, hopefully
  - systempreferences can be dramatically reduced, since most of them are about 
overrides anyways
  - can be done incrementally, replacing one functionality at a time

cons:
  - refactoring doesnt make end users happy (but needs to be done in any case)
  - a bit of work to keep templates happy
  - requires a basic understanding of oop

So to sum up: We already have a working example for circulation (though not in 
production)
that we can demonstrate. It reimplements basically the entire C4::Circulation, 
just some small
parts missing. So it can be done.

But we'd love to hear second opinions from the community! We know the fear for 
breaking changes, but
its neither scary or complicated to implement!

Benjamin Rokseth
Oslo Public Library
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