Add Query#exists? method that bases on :count search_type

lib/chewy/query.rb

@@ -3,6 +3,7 @@
 require 'chewy/query/scoping'
 require 'chewy/query/loading'
 require 'chewy/query/pagination'
+require 'chewy/query/existance'
 
 module Chewy
   # Query allows you to create ES search requests with convenient
@@ -17,6 +18,7 @@ class Query
     include Scoping
     include Loading
     include Pagination
+    include Existance
 
     delegate :each, :count, :size, to: :_collection
     alias_method :to_ary, :to_a

lib/chewy/query/existance.rb

@@ -0,0 +1,13 @@
+module Chewy
+  class Query
+    module Existance
+      # Returns true if there are at least one document that matches the query
+      #
+      #   PlacesIndex.query(...).filter(...).exists?
+      #
+      def exists?
+        search_type(:count).total > 0
+      end
+    end
+  end
+end

spec/chewy/query/existance_spec.rb

@@ -0,0 +1,31 @@
+require 'spec_helper'
+
+describe Chewy::Query::Existance do
+  before { Chewy.massacre }
+
+  before do
+    stub_index(:products) do
+      define_type(:product) do
+        field :name
+        field :age, type: 'integer'
+      end
+    end
+  end
+
+  let(:search) { ProductsIndex.all }
+
+  specify { expect(search.exists?).to eq false }
+
+  context do
+    let(:data) { 10.times.map { |i| {id: i.next.to_s, name: "Name#{i.next}", age: 10 * i.next}.stringify_keys! } }
+
+    before { ProductsIndex::Product.import!(data.map { |h| double(h) }) }
+
+    describe '#count' do
+      specify { expect(search.exists?).to eq true }
+      specify { expect(search.limit(5).exists?).to eq true }
+      specify { expect(search.filter(range: {age: {gt: 20}}).limit(3).exists?).to eq true }
+      specify { expect(search.filter(range: {age: {lt: 0}}).exists?).to eq false }
+    end
+  end
+end