Backport cb4b259 to deprecate behavior removed in 7.x

app/controllers/concerns/blacklight/search_helper.rb

@@ -141,8 +141,9 @@ def fetch_many(ids, user_params, extra_controller_params)
       query = search_builder.
                 with(user_params).
                 where(blacklight_config.document_model.unique_key => ids).
-                merge(extra_controller_params).
-                merge(fl: '*')
+                merge(blacklight_config.fetch_many_document_params || deprecated_fetch_many_document_params).
+                merge(extra_controller_params)
+
       solr_response = repository.search(query)
 
       [solr_response, solr_response.documents]
@@ -152,4 +153,9 @@ def fetch_one(id, extra_controller_params)
       solr_response = repository.find id, extra_controller_params
       [solr_response, solr_response.documents.first]
     end
+
+    def deprecated_fetch_many_document_params
+      Deprecation.warn(self, 'You should configure blacklight_config.fetch_many_document_params; defaulting to { fl: "*" }, but this will be removed in Blacklight 7')
+      { fl: '*' }
+    end
 end

lib/blacklight/configuration.rb

@@ -57,6 +57,7 @@ def default_values
             #rows: 1
           },
           document_pagination_params: {},
+          fetch_many_document_params: nil,
           ##
           # == Response models
           ## Class for sending and receiving requests from a search index

spec/controllers/blacklight/search_helper_spec.rb

@@ -307,6 +307,24 @@ def params
     end
   end
 
+  describe 'Get multiple documents By Id', integration: true do
+    let(:doc_id) { '2007020969' }
+    let(:bad_id) { 'redrum' }
+    let(:response) { subject.fetch([doc_id]).first }
+
+    before do
+      blacklight_config.fetch_many_document_params = { fl: 'id,format' }
+    end
+
+    it 'has the expected value in the id field' do
+      expect(response.documents.first.id).to eq doc_id
+    end
+
+    it 'returns all the requested fields' do
+      expect(response.documents.first['format']).to eq ['Book']
+    end
+  end
+
 # SPECS FOR SPELLING SUGGESTIONS VIA SEARCH
   describe "Searches should return spelling suggestions", :integration => true do
     it 'search results for just-poor-enough-query term should have (multiple) spelling suggestions' do