Post meta validation allows you to validate data stored in WordPress post meta fields. This approach integrates directly with WordPress’s register_meta() function to provide real-time validation for custom fields in the block editor.
When to Use This Approach
Use post meta validation when you need to:
- Validate custom post meta fields
- Ensure required metadata is present for specific post types
- Validate custom field values in real-time as editors type
- Provide accessibility checks for post-level data
Implementation Steps
Step 1: Register Post Meta with Validation in PHP
Register your post meta fields using WordPress’s register_meta() function and integrate with the Block Accessibility Checks validator.
add_action( 'init', array( $this, 'register_custom_meta' ) );
function register_custom_meta() {
// Check if Validator class is available
$validator_class = '\BlockAccessibility\Meta\Validator';
$validator_available = class_exists( $validator_class );
register_meta(
'post',
'custom_field_name',
array(
'single' => true,
'type' => 'string',
'show_in_rest' => true,
'object_subtype' => 'post', // Your post type
'sanitize_callback' => 'sanitize_text_field',
'validate_callback' => $validator_available
? call_user_func(
array( $validator_class, 'required' ),
'post', // Post type
'custom_field_name', // Meta key
array(
'error_msg' => __( 'This field is required.', 'my-plugin' ),
'warning_msg' => __( 'This field is recommended.', 'my-plugin' ),
'description' => __( 'Description of what this field is for', 'my-plugin' ),
'type' => 'settings',
)
)
: null,
)
);
}Step 2: Implement Validation Logic in JavaScript
Create a JavaScript file that hooks into the ba11yc_validate_meta filter to perform client-side validation.
import { addFilter } from '@wordpress/hooks';
addFilter(
'ba11yc_validate_meta',
'my-plugin/validation',
( isValid, value, postType, metaKey, checkName ) => {
// Only validate for your specific post type
if ( postType !== 'post' ) {
return isValid;
}
// Validate based on the meta key
switch ( metaKey ) {
case 'custom_field_name':
if ( checkName === 'required' ) {
// Validate that the field is not empty
return !!( value && value.trim() );
}
break;
}
return isValid;
}
);Step 3: Enqueue Your Validation Script
Ensure your JavaScript validation file is loaded in the block editor with the correct dependencies.
function my_plugin_enqueue_meta_validation_scripts() {
wp_enqueue_script(
'my-plugin-meta-validation',
plugins_url( 'build/meta-validation.js', __FILE__ ),
array(
'wp-hooks',
'wp-i18n',
'block-accessibility-script',
),
'1.0.0',
true
);
}
add_action( 'enqueue_block_editor_assets', 'my_plugin_enqueue_meta_validation_scripts' );Key Concepts
Filter Parameters
The ba11yc_validate_meta filter receives five parameters:
isValid– Current validation state; return this unchanged if your check doesn’t applyvalue– The current value of the meta field being validatedpostType– The post type being edited (e.g., `’post’`, `’page’`, `’band’`)metaKey– The meta key being validated (e.g., `’custom_field_name’`)checkName– The validation check type (e.g., `’required’`)
Validator Class Methods
The Block Accessibility Checks plugin provides a Validator class with built-in validation methods:
required– Validates that a field has a value
call_user_func(
array( $validator_class, 'required' ),
'post_type',
'meta_key',
array(
'error_msg' => __( 'Error message', 'my-plugin' ),
'warning_msg' => __( 'Warning message', 'my-plugin' ),
'description' => __( 'Field description', 'my-plugin' ),
'type' => 'settings',
)
)Multiple Meta Fields
Register and validate multiple meta fields for the same post type:
function register_multiple_meta_fields() {
$validator_class = '\BlockAccessibility\Meta\Validator';
$validator_available = class_exists( $validator_class );
// Field 1
register_meta(
'post',
'field_one',
array(
'single' => true,
'type' => 'string',
'show_in_rest' => true,
'object_subtype' => 'custom_post_type',
'sanitize_callback' => 'sanitize_text_field',
'validate_callback' => $validator_available
? call_user_func(
array( $validator_class, 'required' ),
'custom_post_type',
'field_one',
array(
'error_msg' => __( 'Field One is required.', 'my-plugin' ),
'warning_msg' => __( 'Field One is recommended.', 'my-plugin' ),
'description' => __( 'Description for field one', 'my-plugin' ),
'type' => 'settings',
)
)
: null,
)
);
// Field 2
register_meta(
'post',
'field_two',
array(
'single' => true,
'type' => 'string',
'show_in_rest' => true,
'object_subtype' => 'custom_post_type',
'sanitize_callback' => 'sanitize_text_field',
'validate_callback' => $validator_available
? call_user_func(
array( $validator_class, 'required' ),
'custom_post_type',
'field_two',
array(
'error_msg' => __( 'Field Two is required.', 'my-plugin' ),
'warning_msg' => __( 'Field Two is recommended.', 'my-plugin' ),
'description' => __( 'Description for field two', 'my-plugin' ),
'type' => 'settings',
)
)
: null,
)
);
}JavaScript Validation with Switch Statements
Handle multiple meta fields efficiently using switch statements:
addFilter(
'ba11yc_validate_meta',
'my-plugin/validation',
( isValid, value, postType, metaKey, checkName ) => {
// Only validate for your specific post type
if ( postType !== 'custom_post_type' ) {
return isValid;
}
switch ( metaKey ) {
case 'field_one':
if ( checkName === 'required' ) {
return !!( value && value.trim() );
}
break;
case 'field_two':
if ( checkName === 'required' ) {
return !!( value && value.trim() );
}
break;
case 'field_three':
if ( checkName === 'required' ) {
return !!( value && value.trim() );
}
break;
}
return isValid;
}
);Post Type Specific Validation
The filter automatically receives the post type, making it easy to apply different validations per post type:
addFilter(
'ba11yc_validate_meta',
'my-plugin/validation',
( isValid, value, postType, metaKey, checkName ) => {
// Validate for 'band' post type
if ( postType === 'band' ) {
switch ( metaKey ) {
case 'band_origin':
if ( checkName === 'required' ) {
return !!( value && value.trim() );
}
break;
}
}
// Validate for 'artist' post type
if ( postType === 'artist' ) {
switch ( metaKey ) {
case 'artist_name':
if ( checkName === 'required' ) {
return !!( value && value.trim() );
}
break;
}
}
return isValid;
}
);Important Requirements
For meta validation to work properly:
show_in_rest must be true– Meta fields must be exposed to the REST APICheck Validator class availability– Always verify the Validator class exists before using itMatch post type– Theobject_subtypein PHP must match thepostTypein JavaScriptMatch meta key– The meta key inregister_meta()must match themetaKeyin JavaScript
Testing Your Implementation
- Activate both your plugin and Block Accessibility Checks
- Create or edit a post of the target post type
- Locate your custom meta field in the editor
- Leave the field empty or enter an invalid value
- Check that validation feedback appears in real-time
- Verify the check appears in
Settings>Block Accessibility Checks