pg_searchで簡単に検索機能追加 ref: http://qiita.com/mnishiguchi/items/02d96cdc8575d268a937

Controller

class IngredientsController < ApplicationController

  before_action :search_ingredients, only: :index  # indexアクションのみ

  def index
  end

  ...

  private

    def ingredient_params
      params.require(:ingredient).permit(:name, :volume)
    end

    # 検索用パラメータの有無を検知。検索用パラメータがある場合のみ検索処理。
    def search_ingredients
      @ingredients =  if params[:search].present?
        then Ingredient.search(params[:search])
        else Ingredient.all
        end.sorted.paginate(page: params[:page])
    end
end

Gemfile

#ruby 2.2.1
gem 'rails',       '~> 4.2.1'
gem 'pg',          '~> 0.17.1'
gem 'pg_search',   '~> 1.0.3'   # Named scopes that take advantage of PostgreSQL's full text search
gem 'haml-rails',     '~> 0.9.0'
gem 'bootstrap-sass', '~> 3.2.0.0' # Converts Less to Sass.
# etc

Model

class Ingredient < ActiveRecord::Base
  include PgSearch  # 忘れずincludeすること。

  scope :sorted, ->{ order(name: :asc) }

  pg_search_scope :search,
                  against: [
                    :name,
                    :volume
                  ],
                  using: {
                    tsearch: {
                      prefix: true,
                      normalization: 2
                    }
                  }

...

View

...

# 検索機能
.filter_wrapper{ style: "margin-bottom: 20px;" }
  = form_tag(ingredients_path, method: "get") do
    = text_field_tag :search, nil, placeholder: "Search ingredients ...", class: "form-control"
    = submit_tag "", style: "display: none;"

    ...