ruby on rails如何使用FormOptionHelpers创建动态下拉列表

Question

I have checked some tutorials but I got confused by the parameters in this method

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

I have a map model includes: :area, :system, :file

and I want to read :area from database to a drop down list, and let user choose one

I already did @map = Map.all in the view

what the method should be?

especially the parameter "attribute". In a lot tutorials, people put "id" here. But I don't know what "id" is, and in my situation I don't need any other value, just the "area".

Answer 1

Im not exactly sure what you are asking here but if you are trying to make a dropdown selection for use in an html form will this example help you at all?

<% nations = {'United States of America' => 'USA', 'Canada' => 'Canada', 'Mexico' => 'Mexico', 'United Kingdom'=> 'UK'} %>
<% list = nations.sort %>
<%= f.select :country, list, %>

Here nations is a hash of countries then list becomes the sorted copy of that hash. An html dropdown is then created as a part of the form "f". ":country" is the part of the model that the data is connected to while list is the options to populate the dropdown with

Answer 2

It's not clear from your question what the model is that's being populated with the area.

Typically, collection_select is used between related models.

eg.

class Category < ActiveRecord::Base
  has_many :products
end

class Product < ActiveRecord::Base
  belongs_to :category
end

When selecting the 'category' for a product, your view would have something like:

<%= f.collection_select(:category_id, :id, Category.all, :name, include_blank: true) %>

What this does is specify the Product.category_id as the attribute being populated with the value of Category.id. The values come from the Category.all collection, and with Category.name being the item displayed in the select. The last (optional) parameter says to include a blank entry.

Something like the following is probably what you need:

<%= f.collection_select(:map_id, :id, @map, :area) %>

However, if the model you're trying to populate has an area attribute (instead of an ID linking to the map), you might need to use:

<%= f.collection_select(:area, :area, @map, :area) %>

This specifies that the area attribute of the receiving table will be populated with Map's area attribute, which is also being used as the "description" in the select.