Change the NULLS_LAST SQL syntax to match the adapter type.

Author: natebird

spec/ajax-datatables-rails/datatable/simple_order_spec.rb

@@ -19,7 +19,7 @@
 
       it 'sql query' do
         expect(simple_order.query('email')).to eq(
-          'email DESC NULLS LAST'
+          "email DESC #{nulls_last_sql}"
         )
       end
     end

spec/ajax-datatables-rails/orm/active_record_sort_records_spec.rb

@@ -54,7 +54,7 @@
       datatable.params[:order]['0'] = { column: '0', dir: 'asc' }
       datatable.params[:order]['1'] = { column: '1', dir: 'desc' }
       expect(datatable.sort_records(records).to_sql).to include(
-        'ORDER BY users.username ASC NULLS LAST, users.email DESC NULLS LAST'
+        "ORDER BY users.username ASC #{nulls_last_sql}, users.email DESC #{nulls_last_sql}"
       )
     end
   end
@@ -66,7 +66,7 @@
       nulls_last_datatable.params[:order]['0'] = { column: '0', dir: 'asc' }
       nulls_last_datatable.params[:order]['1'] = { column: '1', dir: 'desc' }
       expect(nulls_last_datatable.sort_records(records).to_sql).to include(
-        'ORDER BY users.username ASC, users.email DESC NULLS LAST'
+        "ORDER BY users.username ASC, users.email DESC #{nulls_last_sql}"
       )
     end
   end

spec/support/test_helpers.rb

@@ -97,3 +97,14 @@ def data
     end
   end
 end
+
+def nulls_last_sql
+  case AjaxDatatablesRails.config.db_adapter
+  when -> (a) { a.in?([:pg, :postgresql, :postgres, :oracle]) }
+    "NULLS LAST"
+  when -> (a) { a.in?([:mysql, :mysql2, :sqlite, :sqlite3]) }
+    "IS NULL"
+  else
+    raise 'unsupported database adapter'
+  end
+end