Jira workflows - Dealing with validator

Recently I got a request to make certain fields mandatory while marking a issue as 'Fix' (A step in our workflow'). Initially I made the requested custom fields as 'Required' in Field configuration, but it screwed !!!. After this change it started asking to provide values for fields which are not visible in 'create' page.
Finally I learnt it needs to be configured in Workflows validator.
I'm sharing my learning's here.

Introduction
Workflow is the place where we define business process. A JIRA workflow is the set of steps (or statuses) and transitions that an issue goes through during its lifecycle.
The below picture represents the default Jira workflow.

JIRA workflows consist of steps and transitions:
  A step represents a workflow's current status for an issue.An issue can exist in one step only at any point in time. In the diagram above the rectangular boxes represent steps/statuses.
 A transition is a link between two steps. A transition allows an issue to move from one step to another step. A transition is a one-way link, so if an issue needs to move back and forth between two steps, two transitions need to be created. In the diagram above the arrows represent transitions.



Workflow Administration
Creating Workflow:  Login -> Administration -> Workflows -> Add new Workflow  (Give name & desc)
Editing a workflow: 
   Inactive workflow:  You can simply edit steps & transition
   Active workflow:  Not possible to edit active workflow directly. 
         Create draft -> Edit  & validate ->  Publish -> Backup old workflow

• Login ->  Administration -> Workflows  -> Choose your workflow -> Edit
• There are two types of edit mode, Diagram and Text

How to make a field mandatory during a workflow transition change ?
Request: In the “Fix” page, (when the bug is marked as fixed), Make the following fields as mandatory
1) Fixed in build 2) Fixed in Iteration 3) Code reviewed by 4) Fix description

Solution:
Using Diagram edit mode.

• Login ->  Administration -> Workflows  -> Choose your workflow -> Edit 
• Using workflow diagram I tracked my workflow steps involved in the transition. The source step is 'New' and destination is 'Assigned to QE' through the transition label 'Fix - Release to QE'. 
• Click on round wheel as shown above and select 'View Validators'
• Click Add a new validator -> Select 'Fields Required' -> Add -> Select the custom fields names (in my case its 'Fixed in build', 'Fixed in Iteration', etc -> Add.
• Publish and Take backup
• That's it
• Alternatively to do the same from Text mode
• Select workflows ->  Edit in Text mode -> Create Draft 
• Find the Step name (in my case its 'New') and the transition ( In my case 'Assign to QE') -> Click on the transition -> Validators -> Add -> Fields Required
• Publish & Backup