pg_search builds ActiveRecord named scopes that take advantage of PostgreSQL’s full text search

Gemfile

gem 'pg_search'

app/controllers/posts_controller.rb

def index
if params[:query].present?
  @posts = Post.order(created_at: :desc).global_search(params[:query])
else
  @posts = Post.order(created_at: :desc)
end
end

app/models/post.rb - search by title

include PgSearch::Model
# pg_search_scope :global_search, against: :title

OR app/models/post.rb - search by title AND content

include PgSearch::Model
pg_search_scope :global_search, against: [:title, :content], using: { tsearch: { prefix: true } }

OR app/models/post.rb - search by title AND content AND associations

include PgSearch::Model
pg_search_scope :global_search, associated_against: { tags: [:name, :category], user: :email, :title, :content }

app/views/posts/index.html.erb

<%= form_with(url: posts_url, method: :get) do |f| %>
  <%= label_tag(:query, "Search for") %>
  <%= text_field_tag(:query) %>
  <%= submit_tag("Search", class: "btn btn-primary") %>
<% end %>