Handle edge case where there is a GSI with the same hash key as the primary index

In the current implementation, when a `where` query is performed with a hash key and range key that would match a GSI, but the hash key overlaps with the primary index, the GSI is not selected and an expensive Scan is performed instead of the cheap Query.

Author: atyndall

lib/dynamoid/criteria/key_fields_detector.rb

@@ -39,8 +39,6 @@ def detect_keys
             @range_key = lsi.range_key
             @index_name = lsi.name
           end
-
-          return
         end
 
         # See if can use any global secondary index
@@ -49,7 +47,7 @@ def detect_keys
         # get back full data
         @source.global_secondary_indexes.each do |_, gsi|
           next unless @query.keys.map(&:to_s).include?(gsi.hash_key.to_s) && gsi.projected_attributes == :all
-          next if @range_key.present? && !query_keys.include?(gsi.range_key.to_s)
+          next if @hash_key.present? && !query_keys.include?(gsi.range_key.to_s)
 
           @hash_key = gsi.hash_key
           @range_key = gsi.range_key

spec/dynamoid/criteria/chain_spec.rb

@@ -666,6 +666,7 @@ def request_params
           global_secondary_index hash_key: :city, range_key: :age, name: :cityage, projected_attributes: :all
           global_secondary_index hash_key: :city, range_key: :gender, name: :citygender, projected_attributes: :all
           global_secondary_index hash_key: :email, range_key: :age, name: :emailage, projected_attributes: :all
+          global_secondary_index hash_key: :name, range_key: :age, name: :nameage, projected_attributes: :all
         end
       end
 
@@ -766,6 +767,15 @@ def request_params
         expect(chain.key_fields_detector.range_key).to eq(:gender)
         expect(chain.key_fields_detector.index_name).to eq(:citygender)
       end
+
+      it 'uses global secondary index when secondary hash key overlaps with primary hash key and range key matches' do
+        chain = Dynamoid::Criteria::Chain.new(model)
+        expect(chain).to receive(:pages_via_query).and_call_original
+        expect(chain.where(name: 'Bob', age: 10).to_a.size).to eq(1)
+        expect(chain.key_fields_detector.hash_key).to eq(:name)
+        expect(chain.key_fields_detector.range_key).to eq(:age)
+        expect(chain.key_fields_detector.index_name).to eq(:nameage)
+      end
     end
 
     it 'supports query on global secondary index with correct start key without table range key' do