Rails 5形成字段到自定义参数

Question

I have a class Reservation in which I want to put a collection (HABTM) of Resources, through an intermidiate class of ReservedResources. This is not a classic HABTM as in ReservedResources I want to store the quantity of the resource reserved.

On the form I want to display the available resources dynamically, something like this:

    <% @resources.each do |r| %>
        <%= f.label "#{r.name}" %>
        <%= f.number_field "reserved_resources#{r.id}".intern %><br>
    <% end %>

The problem is that there is no method named "reserved_resourcesXX", where XX is the resource ID. I want to store the quantity of the resource per its ID on the params hash, but I can't manage to do that...

Is it possible? If so, how? I want to avoid JS for this...

Answer 1

I'll just start off with an example which I guess will get you going.

Scenario

Imagine a store selling products. Users can reserve products to later buy them. They can also define how many of each product they want to reserve.

class User
  has_many :reservations
  has_many :products, through: :reservations
end

class Product
  has_many :reservations
  has_many :users, through: :reservations
end

class Reservation
  belongs_to :user
  belongs_to :product
end

Now when creating your reservations model you can simply add an extra field quantity , resulting in this reservations schema:

create_table "reservations" do |t|
  t.integer  "user_id",
  t.integer  "product_id",
  t.integer  "quantity",
  t.datetime "created_at"
  t.datetime "updated_at"
end

So you take a basic HABTM relationship and add the extra field. Thats exactly what HABTM is for, to add extra info when it is required.

Your usecase

Adapt this to your models and I assume the html forms will be kinda straightforward from there on.

Answer 2

Actually what you should have is something like:

class Reservation < ApplicationRecord
  has_many :reserved_resources
  has_many :resources, through: :reserved_resources
end

class Resource < ApplicationRecord
  has_many :reserved_resources
  has_many :reservations, through: :reserved_resources
end

class ReservedResource < ApplicationRecord
  belongs_to :reservation
  belongs_to :resource
end

Now assuming you have reserved_quantity attribute in reserved_resources table.

Example of use from rails console:

resource = Resource.create(name: 'resource 1')
reservation = Reservation.create(name: 'reservation 1')
resource.reserved_resources.create(reservation: reservation, resource_quantity: 20)

reservation = Reservation.create(name: 'reservation 2')
resource.reserved_resources.create(reservation: reservation, resource_quantity: 10)

Sanity check:

resource.reservations.count
=> 2

you can then get total quantity of reserved resources for a particular resource by doing:

resource.reserved_resources.sum(:resource_quantity)
 => 30