On Jan 19, 1:45 pm, Christian MICHON <[email protected]>
wrote:
> Hi,
>
> I've a portion of code (a checksum) which is commonly used in a
> specific app I just did. I've dozens of models, if not more, and for
> each I've been copying the portion of code.
>
> This seemed to be a good place for a DRY approach, by either using
> mixins or plugins. I've questions.
>
> - which one would be easier ? I did not manage to make a clean mixin,
> since I need to invoke some methods like columns().
If by mixin you mean plain ruby module, that's fine. A plugin is
useful if you want to share it across multiple applications, or if you
want to include both class methods and instance methods (or dataset
methods), but may be overkill if it is for just instance methods in
one internal app.
> - developping a local plugin (without inserting it back into the gem)
> seems interesting, but then how to load it ?
As long as the plugin is available at sequel/plugins/___.rb and named
correctly in the Sequel::Plugins namespace, you'll be able to load it
with Model.plugin just like you load the plugins that ship with
Sequel.
> - I did not manage to find proper guidelines for developping plugins.
> Is there such guideline ?
Other than the RDoc documentation for Sequel::Plugins, no.
> It seems that this is the bare minimum to have in most plugins I saw:
>
> module Sequel
> module Plugins
> module MyOwnChecksum
> def self.apply(model, opts={}, &block)
> model.send(:include, ::MyOwnChecksum)
> end
> def self.configure(model, opts={}, &block)
> end
> module ClassMethods
> end
> module InstanceMethods
> end
> module DatasetMethods
> end
> end
> end
> end
>
> - Is this a decent/correct skeleton ?
The true bare minimum is:
module Sequel
module Plugins
module MyOwnChecksum
end
end
end
as all parts are optional. Your skeleton has the wrong apply method,
you should not call include with the plugin module. The Model.plugin
method handles loading the ClassMethods, InstanceMethods, and
DatasetMethods modules correctly.
> - I need to memoize in a class variable the columns list (I'm making a
> custom checksum, excluding some columns and therefore I do not wish to
> calculate at each checksum the list of columns to exclude). How to
> insert this class variable inside the plugin ?
Class variables are almost certainly the wrong approach. You probably
want to use class instance variables (instances variables of the
class). This is fairly easy to do by adding an attr_accessor in
ClassMethods and calling that method on the class itself.
Jeremy
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