{"id":1309,"date":"2022-08-30T15:15:27","date_gmt":"2022-08-30T15:15:27","guid":{"rendered":"https:\/\/unknownerror.org\/index.php\/2013\/11\/10\/undefined-method-on-has_many-through-collection-of-common-programming-errors\/"},"modified":"2022-08-30T15:15:27","modified_gmt":"2022-08-30T15:15:27","slug":"undefined-method-on-has_many-through-collection-of-common-programming-errors","status":"publish","type":"post","link":"https:\/\/unknownerror.org\/index.php\/2022\/08\/30\/undefined-method-on-has_many-through-collection-of-common-programming-errors\/","title":{"rendered":"Undefined Method on has_many :through-Collection of common programming errors"},"content":{"rendered":"

I have three models:<\/p>\n

Class Project < ActiveRecord::Base\n  has_many :tasks\n  has_many :tags, :through => :tasks\nend\n\nClass Tasks < ActiveRecord::Base\n  belongs_to :project\n  has_and_belongs_to_many :tags\nend\n\nClass Tags < ActiveRecord::Base\n  has_and_belongs_to_many :tasks\n  has_many :projects, :through => :tasks\n<\/code><\/pre>\n
When I open up console, I can get my Project and Task information as expected:<\/p>\n
Tag.find(1).projects\nTag.find(1).tasks\n<\/code><\/pre>\n
If I want, I can get all the tasks for each project regardless of the tag:<\/p>\n
Project.find(1).tasks\n<\/code><\/pre>\n
For whatever reason, I can’t access tasks if I get projects by tag… something = Tag.find(1).projects something.tasks<\/p>\n
…I get the error:<\/p>\n
undefined method `tasks' for #\n<\/code><\/pre>\n
I’ve looked for a couple hours and can’t find anything that corrects this problem. Based on everything I’ve found, it should be working… but it’s not.<\/p>\n
I’m using Rails 3.2.3.<\/p>\n
    \n
  1. \n
    Shouldn’t Tag.find(1).tasks<\/code> give you the same result?<\/p>\n
    Anyway, the problem you’re facing is that you’re trying to retrieve an association from a Relation<\/code> object instead of an instance of your model. Relations<\/code> can be used to chain query conditions, but you can’t directly reference associations from them. So, to get your example working, you’d need to do<\/p>\n
    p = Tag.find(1).projects.includes(:tasks)\n<\/code><\/pre>\n
    Then reference tasks like this: p[0].tasks<\/code>.<\/p>\n
    However I’d just make sure that Tag.find(1).tasks<\/code> will generate the same SQL and ultimately return the same collection of tasks<\/code>.<\/p>\n<\/li>\n<\/ol>\n
    Originally posted 2013-11-10 00:15:58. <\/small><\/p>","protected":false},"excerpt":{"rendered":"
    I have three models: Class Project < ActiveRecord::Base has_many :tasks has_many :tags, :through => :tasks end Class Tasks < ActiveRecord::Base belongs_to :project has_and_belongs_to_many :tags end Class Tags < ActiveRecord::Base has_and_belongs_to_many :tasks has_many :projects, :through => :tasks When I open up console, I can get my Project and Task information as expected: Tag.find(1).projects Tag.find(1).tasks If I […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1309","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/1309","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/comments?post=1309"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/1309\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=1309"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=1309"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=1309"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}