Fix manually adding and id to association

Fixes activeadmin#5236

lib/active_admin/inputs/filters/select_input.rb

@@ -15,7 +15,7 @@ def searchable_method_name
             "#{reflection.through_reflection.name}_#{reflection.foreign_key}"
           else
             name = method.to_s
-            name.concat '_id' if reflection
+            name.concat "_#{reflection.association_primary_key}" if reflection_searchable?
             name
           end
         end
@@ -48,6 +48,10 @@ def pluck_column
           klass.reorder("#{method} asc").distinct.pluck method
         end
 
+        def reflection_searchable?
+          reflection && !reflection.polymorphic?
+        end
+
       end
     end
   end

spec/unit/filters/filter_form_builder_spec.rb

@@ -311,6 +311,28 @@ def filter(name, options = {})
       end
     end
 
+    context "when given the name of relationship with a primary key other than id" do
+      let(:resource_klass) {
+        Class.new(Post) do
+          belongs_to :kategory, class_name: "Category", primary_key: :name, foreign_key: :title
+
+          def self.name
+            "SuperPost"
+          end
+        end
+      }
+
+      let(:scope) do
+        resource_klass.search
+      end
+
+      let(:body) { Capybara.string(filter :kategory) }
+
+      it "should use the association primary key" do
+        expect(body).to have_selector("select[name='q[kategory_name_eq]']")
+      end
+    end
+
     context "as check boxes" do
       let(:body) { Capybara.string(filter :author, as: :check_boxes) }