How to add dynamic fields with condition?

Question

I have a website that is about automobiles, I want when a user choose a brand drupal shows some of its models:

This image show an example:

for example I want when a user selected BMW drupal shows BMW's models in other select tag dynamic. and for example selected Lamborghini drupal shows Lamborghini's models.

I mean a tree stystem

Answer 1

I would recommend you to use any one of following modules.

Hierarchical Select

This module defines the "hierarchical_select" form element, which is a greatly enhanced way for letting the user select items in a hierarchy.

Simple hierarchical select

Simple hierarchical select defines a new form widget for taxonomy fields to select a term by "browsing" through the vocabularies hierarchy.

Taxonomy Term Reference Tree Widget

This module provides an expandable tree widget for the Taxonomy Term Reference field in Drupal 7. This widget is intended to serve as a replacement for Drupal's core Taxonomy Term Reference widget, which is a flat list of radio buttons or checkboxes and not necessarily fit for medium to large taxonomy trees.

Answer 2

You can check the conditionnal fields module which is based on the States API if you want to do this hardcoded.

An other way to do this is by using hierarchical taxonomy and a module like Hierarchical Select even though you might be limited.