Custom RecordView controller for checking if a specific related record(s) exists in a subpanel at time parent record is viewed.

record.js

({
	/* File: ./custom/modules/<Module>/clients/base/views/record/record.js */

	extendsFrom: 'RecordView',
	
	initialize: function(options){
		/* Check if related module has records linked to current record and meet a specific criteria (filter)
		*  You need the "link" field name from vardefs for the specific
		*  subpanel you wish to check. 
		*
		*  This example will check the 'Calls' subpanel for calls where name equals 'Test Call'.
		*/
		this.once('init', function(){
			var subpanelRecs = this.model.getRelatedCollection('calls'); 
		
			subpanelRecs.once('reset', function(collection){
				//Check how many records are in subpanel, if 0, show an alert
				var numRecs = collection.length; 
				if (numRecs === 0)
				{
					app.alert.show('NoRecs', {
						level: 'warning',
						title: app.lang.get('LBL_ALERT_TITLE', this.module), 
    					messages: app.lang.get('LBL_ALERT_MESSAGE', this.module),
    					autoClose: false
					});
				}
			}, this);
			
			subpanelRecs.fetch({
				filter: [{'name':{'$equals':'Test Call'}}],
				relate:true
			});
			
		}, this);

		this._super('initialize', [options]);
	},

	_dispose: function(){
		this._super('_dispose');
	}
})