rails model association using has_many: through - ruby-on-rails

Question

i have a lessons table and a tags table. i associate both of the them using a has_many :through relationship and my middle table is tags_relationship.rb
class Lesson < ActiveRecord::Base
attr_accessible :title, :desc, :content, :tag_name
belongs_to :user
has_many :tag_relationships
has_many :tags, :through => :tag_relationships
end
class Tag < ActiveRecord::Base
attr_accessible :name
has_many :tag_relationships
has_many :lessons, :through => :tag_relationships
end
in one of my views, im trying to create a a virtual attribute. i have...
<div class="tags">
<%= f.label :tag_name, "Tags" %>
<%= f.text_field :tag_name, data: { autocomplete_source: tags_path} %>
</div>
but my lessons table doesn't have that attribute, tag_name, so it calls my method instead
def tag_name
????????
end
def tag_name=(name)
self.tag = Tag.find_or_initialize_by_name(name) if name.present?
end
however im not sure what to put inside the ????????. im trying to refer the :name attribute inside my tags table.
back then i used a has_many and belongs_to relationship. my lesson belonged to a tag (which was wrong) but i was able to write...
tag.name
and it worked. but since its a has_many :through now, im not sure. i tried using tags.name, Lessons.tags.name, etc but i cant seem to get it to work. how can i refer to the tags table name attribute? thank you

Answer 1

Apologize for my bad english.
When your Lesson was belonged to Tag lesson had only one tag, so your code was right. But now Lesson has many Tags, and it is collection (array in simple words). So, your setter must be more complex:
def tag_names=(names)
names = if names.kind_of? String
names.split(',').map{|name| name.strip!; name.length > 0 ? name : nil}.compact
else
names
end
current_names = self.tags.map(&:name) # names of current tags
not_added = names - current_names # names of new tags
for_remove = current_names - names # names of tags that well be removed
# remove tags
self.tags.delete(self.tags.where(:name => for_remove))
# adding new
not_added.each do |name|
self.tags << Tag.where(:name => name).first || Tag.new(:name => name)
end
end
And getter method should be like this:
def tag_names
self.tags.map(&:name)
end
BTW, finders like find_by_name are deprecated. You must use where.