Rails - add a dropdown selection to index with db update on change - ruby-on-rails

Question

I've added dropdown selections to forms before, but am having trouble getting them to work in the index view. I've read the API on this and can't get anything to work.
Basically, I've got a list of all tasks in the index view. I set the default in the db to 'No' in a migration. I want to be able to loop through all the tasks and have a dropdown selection appear with the options no, yes and partly. Then I want to be able to have the db update that task's field with the selection when it is made.
I can't get the dropdown to work - whenever I try using task.select, it says that select is a private method. I apologise, I'm fairly new to rails - any help anyone could give would be fantastic! How do I get the dropdown to work and how do I ensure that the db gets updated when the value is changed?
Thanks!
View code (here's what I have so far) - tasks/index:
<table class="table table-striped table-bordered">
<tr>
<th>Name</th>
<th>Category</th>
<th>Notes</th>
<th>Completed?</th>
<th></th>
<th></th>
<th></th>
</tr>
<% #tasks.each do |task| %>
<tr>
<td><%= task.name %></td>
<td><%= task.category %></td>
<td><%= task.notes %></td>
<td><%= task.select :complete, ['No','Yes','Partly'], :selected => 'No' %></td>
<td><%= link_to 'Show', task %></td>
<td><%= link_to 'Edit', edit_task_path(task) %></td>
<td><%= link_to 'Delete', task, confirm: 'Are you sure?', method: :delete %></td>
</tr>
<% end %>
</table>
UPDATE:
After more research, I've changed the line of code:
<td><%= task.select :complete, ['No','Yes','Partly'], :selected => 'No' %></td>
to:
<% form_for task do |f| %>
<td><%= select :task, :complete, [ ["Yes",2], ["Partly",1], ["No",0]] %></td>
<% end %>
This has stopped throwing up errors when I try and load the page, however, there is nothing where the 'form' should be - and nothing in the source code, these lines are skipped. How can I get this form to appear and how can I get it to change the database when the selection is changed? Thanks!

Answer 1

Suppose that Post::CATEGORIES = ["No", "Yes", "Partly"]
It depends on how you store task.category in your DB.
If it is an integer in (0, 1, 2)
form_for task do |f|
f.select :category, Post::CATEGORIES.map { |c| [c, Post::CATEGORIES.index(c)] }, :selected => task.category, :include_blank => true
end
If it is a string in ("No", "Yes", "Partly")
form_for task do |f|
f.select :category, Post::CATEGORIES, :selected => task.category, :include_blank => true
end
To be able to make a change to your models, you'll of course need to submit the form somehow. You could use one form for all the records with:
One submit button: you'll need to change the form and your update controller to receive multiple tasks
A form per task with multiple submit buttons: your user will need to submit each time he changes the category
Submit using AJAX each time the user changes the category.
Good luck

Answer 2

I think what you're looking for is a form_for and then a f.select. You need to create the form first and then f.select is the drop down. Something like this:
form_for task do |f|
f.select("task", "category", Post::CATEGORIES, {:include_blank => true})
end
replace Post::CATEGORIES with the list of options for the dropdown