MONGOID-4960 Create an exception subclass for calling estimated_count on models with default scopes (#5458)

* MONGOID-4960 Create an exception subclass for calling estimated_count on models with default scopes

* MONGOID-4960 add test

* MONGOID-4960 use count instead

Author: neilshweky

lib/config/locales/en.yml

@@ -181,8 +181,13 @@ en:
           message: "Invalid criteria for estimated_count."
           summary: "Estimated count is strictly a collection-level operation and cannot be called
             on a filtered criteria."
-          resolution: "Try calling estimated_count directly on the class: %{class_name}.estimated_count.\n\n
-            \_If the class defines a default scope, use unscoped: %{class_name}.unscoped.estimated_count."
+          resolution: "Try calling estimated_count directly on the class: %{class_name}.estimated_count."
+        invalid_estimated_count_scoping:
+          message: "Invalid criteria for estimated_count."
+          summary: "Estimated count is strictly a collection-level operation and cannot be called
+            on a model that uses a default scope."
+          resolution: "Try calling estimated_count using unscoped: %{class_name}.unscoped.estimated_count.
+            Alternatively, the #count method can be used, which is usable with scoping."
         invalid_expression_operator:
           message: "Invalid expression operator '%{operator}'."
           summary: "You misspelled an operator, are using an operator that

lib/mongoid/contextual/mongo.rb

@@ -73,7 +73,11 @@ def count(options = {}, &block)
       # @return [ Integer ] The number of matches.
       def estimated_count(options = {})
         unless self.criteria.selector.empty?
-          raise Mongoid::Errors::InvalidEstimatedCountCriteria.new(self.klass)
+          if klass.default_scoping?
+            raise Mongoid::Errors::InvalidEstimatedCountScoping.new(self.klass)
+          else
+            raise Mongoid::Errors::InvalidEstimatedCountCriteria.new(self.klass)
+          end
         end
         view.estimated_document_count(options)
       end

lib/mongoid/errors.rb

@@ -29,6 +29,7 @@
 require "mongoid/errors/invalid_dot_dollar_assignment"
 require "mongoid/errors/invalid_elem_match_operator"
 require "mongoid/errors/invalid_estimated_count_criteria"
+require "mongoid/errors/invalid_estimated_count_scoping"
 require "mongoid/errors/invalid_expression_operator"
 require "mongoid/errors/invalid_field_operator"
 require "mongoid/errors/invalid_relation"

lib/mongoid/errors/invalid_estimated_count_scoping.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module Mongoid
+  module Errors
+
+    class InvalidEstimatedCountScoping < MongoidError
+
+      # Creates the exception raised when trying to call estimated_count
+      # on Model with a default scope
+      #
+      # @param [ String ] class_name The klass of the criteria used to call
+      #                              estimated count.
+      #
+      # @api private
+      def initialize(class_name)
+        super(
+          compose_message(
+            "invalid_estimated_count_scoping",
+            { class_name: class_name }
+          )
+        )
+      end
+    end
+  end
+end

spec/mongoid/contextual/mongo_spec.rb

@@ -223,6 +223,34 @@
         end
       end
     end
+
+    context "when including a default scope" do
+
+      let(:criteria) do
+        Band.where(name: "New Order")
+      end
+
+      before do
+        5.times { Band.create! }
+        Band.default_scope ->{ criteria }
+      end
+
+      after do
+        Band.default_scoping = nil
+      end
+
+      it 'raises an error' do
+        expect do
+          Band.estimated_count
+        end.to raise_error(Mongoid::Errors::InvalidEstimatedCountScoping)
+      end
+
+      it "does not raise an error on unscoped" do
+        expect do
+          expect(Band.unscoped.estimated_count).to eq(5)
+        end
+      end
+    end
   end