Ransack search with ActsAsTaggableOn (#1312)

* Ransack search with ActsAsTaggableOn

* Update acts-as-taggable-on.md

docs/docs/going-further/acts-as-taggable-on.md

@@ -3,18 +3,52 @@ title: Acts-as-taggable-on
 sidebar_position: 13
 ---
 
+## Using Acts As Taggable On
+
 If you have an `ActiveRecord` model and you're using [acts-as-taggable-on](https://github.com/mbleigh/acts-as-taggable-on),
-chances are you might want to search on tagged fields.
+chances are you might want to search on tagged fields. Follow the instructions to install the gem and then set up your project files.
+
+### Configure the model
 
-Suppose you have this model:
+`app/models/tasks.rb`
+
+You can call the tagging field anything you like, it just needs to be plural. No migration is needed as this is stored in the internal ActsAsTaggable tables (`tags` and `taggings`).
 
 ```rb
 class Task < ApplicationRecord
   acts_as_taggable_on :projects
 end
 ```
 
-and you have the following two instances of `Task`:
+### Controller
+
+Add a field to strong params in the controller. Use the singular name with `_list`.
+
+`app/controllers/tasks_controller.rb`
+
+```rb
+def strong_params
+  params
+    .require(:tasks)
+    .permit(:task, :example_field, :project_list)
+```
+
+### Form
+
+We need to `send` the tag fieldname to our model, also using the singular naming.
+
+```
+<div class='form-group'>
+  <%= f.label :project_list %>
+  <%= f.text_field :project_list, value: @task.send(:project_list).to_s %>
+ </div>
+```
+
+Now we can collect our data via the form, with tags separated by commas.
+
+## Ransack Search
+
+Imagine you have the following two instances of `Task`:
 
 ```rb
 { id: 1, name: 'Clean up my room',        projects: [ 'Home', 'Personal' ] }
@@ -31,19 +65,50 @@ When you're writing a `Ransack` search form, you can choose any of the following
 <% end %>
 ```
 
-### Option a - match keys exactly
+### Option A - Match keys exactly
 
 Option `a` will match keys exactly. This is the solution to choose if you want to distinguish 'Home' from 'Homework': searching for 'Home' will return just the `Task` with id 1. It also allows searching for more than one tag at once (comma separated):
 - `Home, Personal` will return task 1
 - `Home, Homework` will return task 1 and 2
 
-### Option b - match key combinations
+### Option B - match key combinations
 
 Option `b` will match all keys exactly. This is the solution if you wanna search for specific combinations of tags:
 - `Home` will return nothing, as there is no Task with just the `Home` tag
 - `Home, Personal` will return task 1
 
-### Option c - match substrings
+### Option C - match substrings
 
 Option `c` is used to match substrings. This is useful when you don't care for the exact tag, but only for part of it:
 - `Home` will return task 1 and 2 (`/Home/` matches both `"Home"` and `"Homework"`)
+
+### Option D - select from a list of tags
+
+In Option D we allow the user to select a list of valid tags and then search againt them. We use the plural name here.
+
+```erb
+<div class='form-group'>
+  <%= f.label :projects_name, 'Project' %>
+  <%= f.select :projects_name_in, ActsAsTaggableOn::Tag.distinct.order(:name).pluck(:name) %>
+</div>
+```
+
+## Multitenancy 
+
+ActsAsTaggableOn allows scoping of tags based on another field on the model. Suppose we have a `language` field on the model, as an effective second level key. We would adjust our model to look like this:
+
+```rb
+class Task < ApplicationRecord
+  acts_as_taggable_on :projects
+  acts_as_taggable_tenant :language
+end
+```
+
+The Ransack search is then filtered using the `for_tenant` method
+
+```
+<div class='form-group'>
+  <%= f.label :projects_name, 'Project' %>
+  <%= f.select :projects_name_in, ActsAsTaggableOn::Tag.for_tenant('fr').distinct.order(:name).pluck(:name) %>
+</div>
+