Don't hit db on method_missing if array doesnt respond.

[ fix #3081 ]

CHANGELOG.md

@@ -224,6 +224,10 @@ For instructions on upgrading to newer versions, visit
 
 ### Resolved Issues
 
+* \#3081 Criteria's `method_missing` now checks if an array responds to the provided
+  method before calling entries in order to not hit the database if a `NoMethodError`
+  was to get raised.
+
 * \#3068 Fixed spec runs on non standard MongoDB ports if `MONGOID_SPEC_PORT` is
   set.
 

lib/mongoid/criteria.rb

@@ -23,6 +23,12 @@ class Criteria
     include Modifiable
     include Scopable
 
+    # Static array used to check with method missing - we only need to ever
+    # instantiate once.
+    #
+    # @since 4.0.0
+    CHECK = []
+
     attr_accessor :embedded, :klass
 
     # Returns true if the supplied +Enumerable+ or +Criteria+ is equal to the results
@@ -322,7 +328,7 @@ def only(*args)
     #
     # @return [ true, false ] If the criteria responds to the method.
     def respond_to?(name, include_private = false)
-      super || klass.respond_to?(name) || entries.respond_to?(name, include_private)
+      super || klass.respond_to?(name) || CHECK.respond_to?(name, include_private)
     end
 
     alias :to_ary :to_a
@@ -506,8 +512,10 @@ def method_missing(name, *args, &block)
         klass.send(:with_scope, self) do
           klass.send(name, *args, &block)
         end
-      else
+      elsif CHECK.respond_to?(name)
         return entries.send(name, *args, &block)
+      else
+        super
       end
     end
 

spec/mongoid/criteria_spec.rb

@@ -3534,6 +3534,59 @@ def self.ages; self; end
     end
   end
 
+  describe "#method_missing" do
+
+    let(:criteria) do
+      Person.all
+    end
+
+    context "when the method exists on the class" do
+
+      before do
+        Person.should_receive(:minor).and_call_original
+      end
+
+      it "calls the method on the class" do
+        expect(criteria.minor).to be_empty
+      end
+    end
+
+    context "when the method exists on the criteria" do
+
+      before do
+        criteria.should_receive(:to_criteria).and_call_original
+      end
+
+      it "calls the method on the criteria" do
+        expect(criteria.to_criteria).to eq(criteria)
+      end
+    end
+
+    context "when the method exists on array" do
+
+      before do
+        criteria.should_receive(:entries).and_call_original
+      end
+
+      it "calls the method on the criteria" do
+        expect(criteria.at(0)).to be_nil
+      end
+    end
+
+    context "when the method does not exist" do
+
+      before do
+        criteria.should_receive(:entries).never
+      end
+
+      it "raises an error" do
+        expect {
+          criteria.to_hash
+        }.to raise_error(NoMethodError)
+      end
+    end
+  end
+
   describe "#uniq" do
 
     let!(:band_one) do