Narrowing search with ransack - ruby-on-rails

Question

I've got workers, workers has many posts. I want to be able to search for a worker, displaying all his posts, then narrow down to the date the posts where made. I can search by name of the worker but when I try to search for date aswell it just displays all posts for that worker (if the date exists in one post).
what I'm trying to run with:
controller:
#q = Worker.ransack(params[:q])
#workers = #q.result.order(name: :asc).includes(:posts).uniq
view:
<%= search_form_for #q do |f| %>
<%= f.label :name_cont %>
<%= f.search_field :name_cont %>
<%= f.label :posts_date_start %>
<%= f.search_field :posts_date_start %>
<%= f.submit %>
<% end %>
<% #workers.each do |worker| %>
<% worker.posts.group_by { |t| t.date.to_time.beginning_of_month }.each do |month, posts| %>
<some table header logic>
<% posts.each do |post| %>
<table content>

Answer 1

Unless you created a custom predicate of start, that will not work.
From your group_by statement I can see that your posts has a date field. If you wanted posts only for the date specified you would use the eq predicate
<%= f.search_field :posts_date_eq %>
If you need to massage your user input, I would look into making a custom predicate you can look at how to do that here -> creating custom predicates
EDIT
To test parsing your date field string into a date put
begin
params[:q][:posts_date_eq] = Date.parse(params[:q][:posts_date_eq])
rescue
# no param present
end
before your search object
#q = Worker.ransack(params[:q])

Answer 2

I solved it like this
instead of
<% worker.posts.group_by { |t| t.date.to_time.beginning_of_month }.each do |month, posts| %>
I did
<% Post.search_post(params[:search_post]).search_post_present(params[:search_post_present]).where(worker_id: worker.id).order(date: :asc).group_by { |t| t.date.to_time.beginning_of_month }.each do |month, posts| %>
that pointed to a search hepler in post.rb
def self.search_post(search_post)
if search_post
where('date LIKE ?', "%#{search_post}%")
else
all
end
end
I then overlapped the forms for both ransack and this search, so both are run with the same submit button, and that worked just fine.