Question

I am going through the Rails API docs for collection_select and they are god-awful.

The heading is this:

collection_select(object, method, collection, value_method, text_method, options = {}, html_options = {})

And this is the only sample code they give:

collection_select(:post, :author_id, Author.all, :id, :name_with_initial, :prompt => true)

Can someone explain, using a simple association (say a User has_many Plans, and a Plan belongs to a User), what I want to use in the syntax and why?

Edit 1: Also, it would be awesome if you explained how it works inside a form_helper or a regular form. Imagine you are explaining this to a web developer that understands web development, but is ‘relatively new’ to Rails. How would you explain it?

Answer 1

collection_select(
    :post, # field namespace 
    :author_id, # field name
    # result of these two params will be: <select name="post[author_id]">...

    # then you should specify some collection or array of rows.
    # It can be Author.where(..).order(..) or something like that. 
    # In your example it is:
    Author.all, 

    # then you should specify methods for generating options
    :id, # this is name of method that will be called for every row, result will be set as key
    :name_with_initial, # this is name of method that will be called for every row, result will be set as value

    # as a result, every option will be generated by the following rule: 
    # <option value=#{author.id}>#{author.name_with_initial}</option>
    # 'author' is an element in the collection or array

    :prompt => true # then you can specify some params. You can find them in the docs.
)

Or your example can be represented as the following code:

<select name="post[author_id]">
    <% Author.all.each do |author| %>
        <option value="<%= author.id %>"><%= author.name_with_initial %></option>
    <% end %>
</select>

This isn’t documented in the FormBuilder, but in the FormOptionsHelper