How to validate Magento 2 form field input value with database table field to find out if already exists?

Question

I have added following affiliate email field (custom attribute) to the customer registration form. Now I want to validate that if value already exists in the database table.

 <div class="control">
        <input type="text" name="affiliate_email" id="affiliate_email" value="<?= $block->escapeHtml($block->getFormData()->getCustomField()) ?>" title="<?= __('CustomField') ?>" class="input-text"  data-mage-init='{"validation":{}}'>
    </div>

What is the best way to do this ?

Answer 1

You can check that if the value is already present or not & also print it there into the input box with the below code

<div class="field custom_attribute">
    <label class="label" for="customer_attribute”><span><?php /* @escapeNotVerified */ echo __('Custom Attribute') ?></span></label>
    <div class="control">
    <?php $affiliate_email = $block->escapeHtml($block->getCustomer()->getCustomAttribute('affiliate_email')->getValue());?>
        <input type="text" name="affiliate_email" id="affiliate_email" value="<?php if(!empty($affiliate_email)){ echo $affiliate_email; } ?>" title="<?php /* @escapeNotVerified */ echo __('Custom Attribute') ?>" class="input-text" data-validate="{required:true}"/>
    </div>
</div>

It will look for that particular attribute & if it is having any value then it will add it as a value into your input field

Answer 2

Where email is your database field value.

data-validate="{required:true, 'validate-email':true,equalTo:'#email'}"