Rails has_many :through PG::Error: ERROR: column reference “id” is ambiguous error

问题

I'm new to rails and I've been trying to get two has_many :though relationships to work out (as opposed to using has_and_belongs_to_many as explained by this post http://blog.flatironschool.com/post/35346328762/why-you-dont-need-has-and-belongs-to-many) but am now running into a Postgres error:

PG::Error: ERROR:  column reference "id" is ambiguous
LINE 1: ...on_id" IS NULL AND "components"."id" = 1 ORDER BY id ASC LIM...
                                                             ^
: SELECT  1 AS one FROM "components" INNER JOIN "collection_components" ON "components"."id" = "collection_components"."component_id" WHERE "collection_components"."collection_id" IS NULL AND "components"."id" = 1 ORDER BY id ASC LIMIT 1
  Rendered collections/_form.html.haml (117.0ms)
  Rendered collections/new.html.haml within layouts/application (143.5ms)
Completed 500 Internal Server Error in 164ms

ActiveRecord::StatementInvalid - PG::Error: ERROR:  column reference "id" is ambiguous
LINE 1: ...on_id" IS NULL AND "components"."id" = 1 ORDER BY id ASC LIM...
                                                             ^

_form.html.haml

= form_for @collection do |f|
  - if @collection.errors.any?
    #error_explanation
      %h1= "#{pluralize(@collection.errors.count, "error")} prohibited this collection from being saved:"
      %ul
        - @collection.errors.full_messages.each do |msg|
          %li= msg

  .field
    - Component.all.each do |component|
      = label_tag :component_ids, component.id
      = check_box_tag :component_ids, component.id, @collection.components.include?(component), :name => 'collection[component_ids][]'
  .field
    = f.label :title
    = f.text_field :title
  .actions
    = f.submit 'Save'

collection_component.rb

class CollectionComponent < ActiveRecord::Base
  attr_accessible :collection_id, 
                  :component_id

  belongs_to      :collection
  belongs_to      :component
end

collection.rb

class Collection < ActiveRecord::Base
  default_scope order('id ASC')

  attr_accessible         :style_id, 
                          :name, 
                          :title,
                          :component

  #has_and_belongs_to_many :components

  has_many                :collection_components, :dependent => :destroy
  has_many                :components, :through => :collection_components

  belongs_to              :style

  validates_presence_of   :style
  validates_presence_of   :title

  before_save             :create_name

  private

  def create_name
    self.name = title.parameterize
  end
end

component.rb

class Component < ActiveRecord::Base
  default_scope order('id ASC')

  attr_accessible         :category_id, 
                          :name, 
                          :title,
                          :collection,
                          :style

  has_many                :collection_components, :dependent => :destroy
  has_many                :collections,   :through => :collection_components

  has_many                :component_styles
  has_many                :styles,        :through => :component_styles

  belongs_to              :category

  validates_presence_of   :category
  validates_presence_of   :title

  before_save             :create_name

  private

  def create_name
    self.name = title.parameterize
  end
end

collection_components table

Column     |            Type             |                             Modifiers                              
---------------+-----------------------------+--------------------------------------------------------------------
 id            | integer                     | not null default nextval('collection_components_id_seq'::regclass)
 collection_id | integer                     | 
 component_id  | integer                     | 
 created_at    | timestamp without time zone | not null
 updated_at    | timestamp without time zone | not null
Indexes:
    "collection_components_pkey" PRIMARY KEY, btree (id)

collections table

Column   |            Type             |                        Modifiers                         
------------+-----------------------------+----------------------------------------------------------
 id         | integer                     | not null default nextval('collections_id_seq'::regclass)
 style_id   | integer                     | 
 name       | character varying(255)      | 
 title      | character varying(255)      | 
 created_at | timestamp without time zone | not null
 updated_at | timestamp without time zone | not null
Indexes:
    "collections_pkey" PRIMARY KEY, btree (id)

components table

   Column    |            Type             |                        Modifiers                        
-------------+-----------------------------+---------------------------------------------------------
 id          | integer                     | not null default nextval('components_id_seq'::regclass)
 name        | character varying(255)      | 
 title       | character varying(255)      | 
 category_id | integer                     | 
 created_at  | timestamp without time zone | not null
 updated_at  | timestamp without time zone | not null
Indexes:
    "components_pkey" PRIMARY KEY, btree (id)

回答1:

Try this:

  default_scope { order('collections.id ASC') } //collection.rb
  default_scope { order('components.id ASC') } //component.rb

When you perform a join ascending on id becomes ambiguous column because both components and collections have id column. It will not know which to use.

回答2:

You just need to add in the query the name of the table before the field.

sql-method("name-of-table.field operator")

Sample: order("collections.id ASC")

This happens because exists many fields called with same name and the interpreter does not identify of who is in the query assembled.

来源：https://stackoverflow.com/questions/15885335/rails-has-many-through-pgerror-error-column-reference-id-is-ambiguous-err

标签

ruby-on-rails

postgresql

has-many-through