Saving arrays in Rails 4.2.3 - ruby-on-rails

Question

I am having some trouble saving arrays in Rails.
Rails version: 4.2.3 | Ruby version: 2.2.1 | DB: PostgreSQL
In my view, I have a collection of check boxes that shows the conferences that my member attended.
<%= f.fields_for :conferences_member do |conference| %>
<%= collection_check_boxes(:conferences_member, :conference_id, #all_conferences, :id, :name)%>
<% end %>
I put a break point (binding.pry) after the create action in my MembersController, and surprisingly, it shows the selected check boxes:
Processing by Database::MembersController#create as HTML
Parameters: {"utf8"=>"✓","authenticity_token"=>"XYZ==",
[...] "conferences_member"=> {"conference_id"=>["3", "5", ""]}, [...]
Now, if I go to rails c, and type ConferencesMember.last to check what was saved, I get:
pry(main)> ConferencesMember.last
ConferencesMember Load (0.5ms) SELECT "conferences_members".* FROM
"conferences_members" ORDER BY "conferences_members"."id" DESC LIMIT 1
=> nil
These are my associations:
#=> member.rb
has_one :conferences_member
accepts_nested_attributes_for :conferences_member, allow_destroy: true, reject_if: :all_blank
#=> conferences_member.rb
serialize :conference_id, Array
belongs_to :member
#=> members_controller.rb
params.require(:member).permit( [...]
:conference_member_attributes => [:id, :member_id, :conference_id => []],
[...])
I want to thank you in advance. I've tried almost everything here on StackOverflow, but I don't see my error.
Thank you again.
EDIT:
More of my MembersController:
def new
#member = Member.new
#member.build_conferences_member
end
def create
#member = Member.new(member_params)
binding.pry
end
The log doesn't show any error, it just shows that conferences were not saved at all.

Answer 1

First, your field needs to be renamed to nest the :conference_id in :conferences_member_attributes (not in :conferences_member as you do now). Take advantage of the form object yielded by fields_for:
<%= f.fields_for :conferences_member do |conference| %>
<%= conference.collection_check_boxes :conference_id, #all_conferences, :id, :name %>
<% end %>
You also need to actually save the record in the create action: Member.new builds the record but does not save it. Typically, the create action branches based on whether the record saved or did not (due to validations). So you might rewrite this method like so:
def create
#member = Member.new(member_params)
# when #member.save returns true, it saved to the db successfully
if #member.save
redirect_to members_path, notice: "Member #{#member.id} saved!"
# otherwise, it didn't save because of a validation error, so we render the error
# to the user and give them a chance to fix it
else
flash[:error] = "Member didn't save: #{#member.errors.full_messages.to_sentence}"
render :new
end
end
Lastly, to make sure your data gets through your strong parameters, check your logs for any messages that parameters were filtered out. The messages look like:
Unpermitted parameters: your_favorite_attribute