redmine_acts_as_taggable_on

redmine_acts_as_taggable_on is a gem which allows multiple Redmine plugins to use the tables provided by acts-as-taggable-on without stepping on each others' toes.

Why?

The problem we ran into when we discovered that both redmine_tags and redmine_knowledgebase want to use the acts-as-taggable-on gem is that after either is installed, the migration for the other fails, since the database tables already exist.

Additionally, the plugins must choose between two less than ideal options when uninstalling:

Drop the tables, destroying data which may still be in use by another plugin
Leave the tables there, violating the user's expectation that the database should be back to how it was before the plugin was installed

redmine_acts_as_taggable_on solves this issue by giving Redmine plugins a mechanism to declare that they require these tables, and providing intelligent migrations which only drop the tables when no other plugins are using them.

redmine_acts_as_taggable_on also provides a limited defence against plugins which directly depend on acts-as-taggable-on. It does this by grepping through their Gemfiles for the string acts-as-taggable-on -- if found, it will treat the plugin as requiring the acts-as-taggable-on tables, and will print a gentle(-ish) suggestion to use this gem instead.

Status and Compatibility

Believed to be stable. The automated tests currently pass on Redmine trunk, 2.3.1, 2.2.4, 2.1.5, and 2.0.4 (which are, at the time of writing, the most recent releases of every 2.x branch). However, this gem is not yet used by any Redmine plugins in the wild.

This gem is not compatible with Redmine 1.x.

Limitations

This gem cannot currently protect against situations where a plugin directly using acts-as-taggable-on has put the generated migration into its db/migrate directory. If a user tries to migrate the plugin down by executing rake redmine:plugins:migrate VERSION=0 NAME=redmine_foo_plugin, the tables will still be dropped, regardless of whether other plugins are still using them.

I'm in two minds about whether to fix this: on the one hand, it would require some nasty monkey-patching. On the other hand, data loss is no fun at all.

Setup

Add it to your plugin's Gemfile:

gem 'redmine_acts_as_taggable_on', '~> 1.0'

Note: Please use the above line verbatim. This is to avoid being told by Bundler that we aren't allowed to use multiple declarations of the same gem with different version requirements.

I've chosen the above requirement to ensure that there are no accidental breakages -- the public API (that is, the following paragraph) will remain the same throughout version 1.0. If it does need to change, I'll bump the major version. This should ensure that Bundler only refuses to bundle when there is an actual incompatibility.

Add the migration:

$ echo 'class AddTagsAndTaggings < RedmineActsAsTaggableOn::Migration; end'\
    > db/migrate/001_add_tags_and_taggings.rb

Declare that your plugin needs redmine_acts_as_taggable_on inside init.rb:

require 'redmine_acts_as_taggable_on/initialize'

Redmine::Plugin.register :my_plugin do
  requires_acts_as_taggable_on
  ...

That's it. Your plugin will now migrate up and down intelligently. For example:

$ cd /path/to/redmine
$ cp -r /some/plugin/using/this/gem       plugins/redmine_foo
$ cp -r /another/plugin/using/this/gem    plugins/redmine_bar
$ rake redmine:plugins:migrate
Migrating redmine_bar (Redmine bar)...
==  AddTagsAndTaggings: migrating =========================================
-- create_table(:tags)
   -> 0.0039s
-- create_table(:taggings)
   -> 0.0007s
-- add_index(:taggings, :tag_id)
   -> 0.0003s
-- add_index(:taggings, [:taggable_id, :taggable_type, :context])
   -> 0.0003s
==  AddTagsAndTaggings: migrated (0.0059s) ================================

Migrating redmine_foo (Redmine foo)...
==  AddTagsAndTaggings: migrating =========================================
-- Not creating "tags" and "taggings" because they already exist
==  AddTagsAndTaggings: migrated (0.0006s) ================================

You can look at the test script to see how other situations are handled.