Forum OpenACS Development: Re: Customizations

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16: Re: Customizations (response to 15)
Posted by Tom Jackson on
What exactly is meant by customization? A long time ago I worked on a site, mydomain.com. The owner/manager had lots of ideas, one was running many similar sites, but with highly customized services. For instance a full featured service would offer DNS, email, web redirection. Besides the feature diffences, each service could have different backend configurations, like separate nameservers or email servers.

Of course, each site would appear as a separate website with custom look.

What a nightmare it would be to churn through all this for slight differences, or merely to avoid security issues. But what about custom pages, new pages for additional functionality?

Anyway, the requirements and my own laziness lead to the development of a single set of tables for all sites, a single instance of ACS4, and an administrative interface which allowed for the instant creation of a new service at the data model level.

Certain things setup in advance greatly help with customization, but the biggest are:

* design for customization
* independent customization code for data model
* complete separation of data from presentation code
* customization aware request processor.

(Shorter version: existence, knowledge and application of tools for Model-View-Controller pattern)

(Even shorter version: integrated separation)

Basically this all boils down to the fact that customization is not an easy add-on. Also inherent in customization is that it is nearly impossible to know in advance what is going to be customized. If customization could be handled by a simple handful of package parameters, it would fall under the heading of configuration, that is, what is allowed is completely defined in advance by the package writer. If this is offered up as customization, developers will quickly argue for new parameters to take into account their changes.

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17: Re: Customizations (response to 16)
Posted by Malte Sussdorff on
Customization here is for those cases where OpenACS does not allow me to work in a separate package or change templates or parameters or callbacks to my liking and where adding functionality to the checked out package to achieve this is not desirable. Basicly anytime you change something in acs-core and do not want to commit it back.
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18: Re: Customizations (response to 17)
Posted by Tom Jackson on
Customization here is...anytime you change something in acs-core and do not want to commit it back.

This is essentially a fork and is already fully supported. This type of customization could be characterized as changes which were not planned for and which nobody wants in the core package.

Instead of asking for changes to support your specific proposed method of customization, why not first change your own request processor and see how well it works for you?

The rp is already complicated and this feature would probably need some examples to show how it works, how it should be used and when. But the proposal appears to require replacing any file which needs any change with a new slightly different file. But for some reason you wish to retain the option of switching back to the original after an update and manual compare/diff. I wonder how the rp will figure out how to ignore the custom files, or which ones to ignore, since an adp and tcl could be changed. Best to not speculate until there is something working and the process can be tested as a whole.

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19: Re: Customizations (response to 18)
Posted by Malte Sussdorff on
"why not first change your own request processor and see how well it works for you"

Because I try to collect feedback from the community before I head in any specific direction, especially when it comes down to coding changes into core. And as you can see from the discussion it sparked, my "implementation" would not have been one generally acceptable.

In the past the change I thought off would work when you wanted to change the login screen for users in acs-subsite/lib/login.adp. I managed to make the location of this file a parameter in 5.4 and now you can store that file in a custom package. I did it this way because none of my clients wants the default login.adp, therefore general usefulness is implied.

But what if a client has changed /acs-admin/www/admin/become.tcl to make an additional permission check for special sysadmin privs which they have in their custom application. None of my other clients wants this. It is not generally useful in OpenACS (I'd assume), so the only options at the moment I have is:

a) Make the location a parameter (yet another one?)
b) Write a callback so others can make additional checks if the want to
c) Rewrite their whole handling of permission checks for sysadmins to just use ACS permissions (they would not pay for that)
d) Fork and always remember there is a change in that file when merging new versions from OpenACS
e) Write /www/acs-admin/admin/become.tcl

a-c) Do not make sense.

d) Is something I would like to avoid and be it for the reason that the client could by accident say "update from repository" and overwrite the change.

Doing d) has the benefit that, when a new version comes out and you use a clever merging tool then chances are that you will not run into any problems and still retain your custom changes. At least for a minor change like this. But what if your whole page has changed? Then it might be better to have a custom version of the file and just look at the changes in the OpenACS version and modify if needed manually.

e) Works beautifully (thanks Don for reminding me about that), but only in packages that you mount *once* (otherwise you would have to do it for every mountpoint).

I have seen client installations where a custom package was used and they included the OpenACS functionality. That works as well, but provides a lot of code and makes code maintenance more difficult (as you need to copy files which are not really needed as well, just to make the custom package provide the minimal functionality needed). At least I initially got confused which package is used and mounted when working on that site.

So the idea of Don's appeals to me most at the moment and if there is the time I will probably investigate it a little bit more. For the time being and my immediate needs I am fine with option e), though I would like to come up with a general plan (best practice) on how to do these kinds of customizations / forks you name it.