How to manipulate in the form the data sent from the browser in symfony 2?

Question

symfony

For example, there is a certain entity with categories. Categories are presented as a tree, each category has an id. There is a document (MongoDB) that has a categories field in which I want to store a flat array of category id's.
In symfony 1, it was possible to write a full-fledged widget that would render any HTML by the value of an object field and a validator that would convert the values ​​sent from the form to any form. Also, in the post form validator, it was also possible to change the values ​​from the form to absolutely any data set.

How can form data be manipulated in the second symphony?

Answer 1

Data Transformers