how to remove records from the joined table? - ruby-on-rails

Question

please help solve the problem.
table posts
create_table "posts", force: :cascade do |t|
t.string "title"
t.text "body"
end
table tags
create_table "tags", force: :cascade do |t|
t.string "tagname"
end
joined table
create_table "posts_tags", id: false, force: :cascade do |t|
t.integer "post_id"
t.integer "tag_id"
end
model Post
class Post < ActiveRecord::Base
has_and_belongs_to_many :tags
end
model Tag
class Tag < ActiveRecord::Base
has_and_belongs_to_many :posts
end
I need to remove some of the association table posts_tags.
I get from the form set id tags:
[3, 18, 21]
Here is my controller that handles this set id_tags:
def update
if #post.update_attributes(post_params)
#add_new_tags(#post)
p '------------------1'
p params['delete_tags']
p '------------------2'
destroy_tags(params['delete_tags'], #post)
flash[:success] = t :post_updated
redirect_to user_post_path(#user, #post)
else
flash[:error] = t :post_not_updated
render 'edit'
end
end
private
def destroy_tags(tags,post)
tags.each do |tag|
p '=================='
p tag
tag_del = post.tags.find_by_post_id(:post_id => post.id)
if teg_del
post.tags.delete(tag_del)
end
end
end
def post_params
params.require(:post).permit(:delete_tags)
end
as a result, I get the following error message:
undefined method `find_by_post' for #<Tag::ActiveRecord_Associations_CollectionProxy:0x007f097ed78ac8>
the console displays the following message:
Processing by PostsController#update as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"jfNoFJVn2dDqIwIdK/SWerFKIPFJ9bTYdWjy4QFBFL8gHrO7TnzhBq4Mcw+uDyDn9atLEAmfcPdlmHBVHMSDHQ==", "post"=>{"title"=>"Corrupti.ggh", "body"=>"Suscipit ut odit labore fugiat quia aliquam."}, "tagnames"=>"", "delete_tags"=>["3", "18", "21"], "commit"=>"Сохранить Post", "locale"=>"ru", "user_id"=>"24", "id"=>"359"}
Post Load (0.2ms) SELECT "posts".* FROM "posts" WHERE "posts"."id" = ? LIMIT 1 [["id", 359]]
User Load (0.1ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", 24]]
User Load (0.1ms) SELECT "users".* FROM "users" WHERE "users"."remember_token" = ? LIMIT 1 [["remember_token", "15166203712e74cc4638f34991c141f85c04a0e0"]]
CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", "24"]]
(0.1ms) begin transaction
(0.0ms) commit transaction
"------------------1"
["3", "18", "21"]
"------------------2"
"=================="
"3"
Completed 500 Internal Server Error in 6ms (ActiveRecord: 0.5ms)

Answer 1

Since you have a join table, the tags table itself doesn't have a post_id, so that find_by won't work. It isn't needed though because post.tags would retrieve all the tags connected to that post anyway.
You get a lot of the functionality for handling habtm relationships and forms out of the box with rails using things like collection_check_boxes where I don't think you need the extra destroy tags method unless I'm misunderstanding what you are trying to accomplish. You might consider adding/removing tag associations to posts like this:
Post - has_and_belongs_to_many :tags
Tag - has_and_belongs_to_many :posts
Post Update Form:
<legend>Tags</legend>
<div class="form-group">
<%= f.collection_check_boxes(:tag_ids, Tag.all, :id, :name) %>
</div>
Make sure to allow :tag_ids => [] in your controller's post_params
The will allow you to update the tags belonging to the post by adding any new tags that were checked and removing any tags that were unchecked in the form and you can have normal create and update controller actions without need for the extra destroy_tags method.