To me the “Cascading Dropdown” feature in SharePoint both on-premises and online is like a never ending story.
I’ve used my fair share of different solutions with different level of difficulty.

“Cascading Dropdown” is the concept of filtering a form control with values from another control.

In this post I’ll guide You through one of my latest finding for SharePoint Online(O365).

First thing first, why will you need “Cascading Dropdown”? | Because it’s “User Friendly”

Example: create a form where user can choose a value in a “Country” field then the next field “City” will filter and display the cities for the chosen country.

Requirements:

Nintex Form for O365
One SharePoint Main List
Two support SharePoint List

First create a support list named Country:

Then create a second support list named City | in the City List create a lookup column “Country” with lookup to the “Country List”

My main list is named “CascadingDropDown” | it has three columns | Title | Country (lookup to country list) | City (lookup to city list)

In the “CascadingDropDown” list in the ribbon choose to customize with Nintex Forms

This will send you to the Nintex Form Designer view | we won’t make any big changes to the form just the “City” field control

Double click on the City field control to bring up the control settings | we will filter the selection based on the “Country” field control

Save and Publish your form | when adding a new item you can now choose “Country” and “City” will filter the selections available

I simply love this solution, because it’s easy to build and works great.

ENJOY!!