Drupal 8 function from controller returns html markups only

Question

I have been creating a table from mysql result , but its printing the html markup only and says controller must return a response . what may be the reason ?

LogicException: The controller must return a response (

(5 rows)group_nameparent_nameEditDeleteSelect itemsL2V9http://192.168.1.236/mailusers/usergroup/edit/6>edithttp://192.168.1.236/mailusers/usergroup/delete/6>delete

L3v3http://192.168.1.236/mailusers/usergroup/edit/7>edithttp://192.168.1.236/mailusers/usergroup/delete/7>deleteAdminsV6http://192.168.1.236/mailusers/usergroup/edit/8>edithttp://192.168.1.236/mailusers/usergroup/delete/8>deleteL4Vodafonehttp://192.168.1.236/mailusers/usergroup/edit/9>edithttp://192.168.1.236/mailusers/usergroup/delete/9>deleteVCNONetworkhttp://192.168.1.236/mailusers/usergroup/edit/12>edithttp://192.168.1.236/mailusers/usergroup/delete/12>delete
given). in Symfony\Component\HttpKernel\HttpKernel->handleRaw() (line 157 of vendor/symfony/http-kernel/HttpKernel.php).

Answer 1

The error message is not pointing in the right direction. It should say:

"The controller must return a render array"

For example the most basic one:

return [
  '#markup' => '<p>This is html markup</p>',
];

Usually the render array is more complex, for example to build a table, see https://www.codimth.com/blog/web/drupal/render-table-drupal-8

The error message is raised by Symfony, and from the stand point of Symfony this is correct. A controller must provide a response, but Drupal has extended the response handling to look for render arrays, that are then used to generate a response with the rendered html. If you don't provide a render array, then there is no response and then this error message will come up.