Embed Fields of an Entity to a Form in Drupal 7

Entities are one of the most important concepts introduced in Drupal 7. It is clear now that, it got further expanded in Drupal 8.

Sometimes requirements may arise that want you to embed/add fields for an entity within a another form, possibly custom form you created in your module. With this article I am trying to show you how to achieve it. I will show it by embedding fields for a page node within a custom form. To keep things simple, the custom form do nothing other than just showing a text input field and allows to add/edit a page node.