How can I use the “trigger.new” and “trigger.newmap” for validating the records?

 In the context of Salesforce, let us consider that you have a custom object whose name is “CustomObject___c” with a related field “relatedField__c”. You aim to enforce a rule related to validation and updating the records based on the value of “relatedField__c” during a before-update trigger.

Here is the example given of how you can achieve this particular target:-

Trigger CustomObjectTrigger on CustomObject__c (before update) {

    // Map to store the old values of RelatedField__c

    Map oldRelatedFieldMap = new Map();

    // Populate the oldRelatedFieldMap with the old values of RelatedField__c

    For (CustomObject__c oldRecord : Trigger.old) {

        oldRelatedFieldMap.put(oldRecord.Id, oldRecord.RelatedField__c);

    }

    // Iterate over the records being updated

    For (CustomObject__c newRecord : Trigger.new) {

        String oldRelatedFieldValue = oldRelatedFieldMap.get(newRecord.Id);

        String newRelatedFieldValue = newRecord.RelatedField__c;

        // Validation rule: Example – Ensure RelatedField__c is not being changed

        If (oldRelatedFieldValue != newRelatedFieldValue) {

            newRecord.addError(‘RelatedField__c cannot be changed.’);

        }

        // Update logic: Example – Set another field based on the value of RelatedField__c

        If (newRecord.RelatedField__c == ‘SpecificValue’) {

            newRecord.AnotherField__c = ‘UpdatedValue’;

        }

    }}