Here I’ve a custom “Student__c” object. There is a validation rule on “Date_of_Birth__c” field, that Date of Birth cannot be greater than today. And I’m using a visualforce page to insert the data in “Student__c” object. So, I need to show the validation rule error message in visualforce page.

Validation Rule:

Below is my controller which gave the solution for displaying validation error message on visualforce page.

Controller:

public with sharing class StudentExt {

    public Student__c student{get;set;}
    
    public StudentExt(ApexPages.StandardController controller) {
        student = (Student__c)controller.getRecord();
    }
    
    public Pagereference saveStudent() {
        try {
            Upsert student;
            return new Pagereference('/' + student.Id);
        }
        catch(DMLException de) {
            Apexpages.addMessage(new ApexPages.Message(ApexPages.SEVERITY.FATAL, de.getDmlMessage(0)));
            return NULL;
        }
        catch(Exception e) {
            Apexpages.addMessage(new ApexPages.Message(ApexPages.SEVERITY.FATAL, e.getMessage()));
            return NULL;
        }
    }
}

Visualforce Page

<apex:page standardController="Student__c" extensions="StudentExt" >
    <apex:pageMessages id="errormsg" />
    <apex:form >
        <apex:pageBlock >
            <apex:pageBlockButtons >
                <apex:commandButton value="Save" action="{!saveStudent}" reRender="errormsg"/>
                <apex:commandButton value="Cancel" action="{!Cancel}"/>
            </apex:pageBlockButtons>
            
            <apex:pageBlockSection columns="2" title="Information">
                <apex:inputField value="{!Student__c.First_Name__c}"/>
                <apex:inputField value="{!Student__c.Last_Name__c}"/>
                <apex:inputField value="{!Student__c.Date_of_Birth__c}"/>
                <apex:inputField value="{!Student__c.Address__c}"/>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>