WooCommerce: custom variations settings

gistfile1.php

<?php

// Add Variation Settings
add_action( 'woocommerce_product_after_variable_attributes', 'variation_settings_fields', 10, 3 );

// Save Variation Settings
add_action( 'woocommerce_save_product_variation', 'save_variation_settings_fields', 10, 2 );

/**
 * Create new fields for variations
 *
*/
function variation_settings_fields( $loop, $variation_data, $variation ) {

	// Text Field
	woocommerce_wp_text_input( 
		array( 
			'id'          => '_text_field[' . $variation->ID . ']', 
			'label'       => __( 'My Text Field', 'woocommerce' ), 
			'placeholder' => 'http://',
			'desc_tip'    => 'true',
			'description' => __( 'Enter the custom value here.', 'woocommerce' ),
			'value'       => get_post_meta( $variation->ID, '_text_field', true )
		)
	);

	// Number Field
	woocommerce_wp_text_input( 
		array( 
			'id'          => '_number_field[' . $variation->ID . ']', 
			'label'       => __( 'My Number Field', 'woocommerce' ), 
			'desc_tip'    => 'true',
			'description' => __( 'Enter the custom number here.', 'woocommerce' ),
			'value'       => get_post_meta( $variation->ID, '_number_field', true ),
			'custom_attributes' => array(
							'step' 	=> 'any',
							'min'	=> '0'
						) 
		)
	);

	// Textarea
	woocommerce_wp_textarea_input( 
		array( 
			'id'          => '_textarea[' . $variation->ID . ']', 
			'label'       => __( 'My Textarea', 'woocommerce' ), 
			'placeholder' => '', 
			'description' => __( 'Enter the custom value here.', 'woocommerce' ),
			'value'       => get_post_meta( $variation->ID, '_textarea', true ),
		)
	);

	// Select
	woocommerce_wp_select( 
	array( 
		'id'          => '_select[' . $variation->ID . ']', 
		'label'       => __( 'My Select Field', 'woocommerce' ), 
		'description' => __( 'Choose a value.', 'woocommerce' ),
		'value'       => get_post_meta( $variation->ID, '_select', true ),
		'options' => array(
			'one'   => __( 'Option 1', 'woocommerce' ),
			'two'   => __( 'Option 2', 'woocommerce' ),
			'three' => __( 'Option 3', 'woocommerce' )
			)
		)
	);

	// Checkbox
	woocommerce_wp_checkbox( 
	array( 
		'id'            => '_checkbox[' . $variation->ID . ']', 
		'label'         => __('My Checkbox Field', 'woocommerce' ), 
		'description'   => __( 'Check me!', 'woocommerce' ),
		'value'         => get_post_meta( $variation->ID, '_checkbox', true ), 
		)
	);

	// Hidden field
	woocommerce_wp_hidden_input(
	array( 
		'id'    => '_hidden_field[' . $variation->ID . ']', 
		'value' => 'hidden_value'
		)
	);

}

/**
 * Save new fields for variations
 *
*/
function save_variation_settings_fields( $post_id ) {

	// Text Field
	$text_field = $_POST['_text_field'][ $post_id ];
	if( ! empty( $text_field ) ) {
		update_post_meta( $post_id, '_text_field', esc_attr( $text_field ) );
	}
	
	// Number Field
	$number_field = $_POST['_number_field'][ $post_id ];
	if( ! empty( $number_field ) ) {
		update_post_meta( $post_id, '_number_field', esc_attr( $number_field ) );
	}

	// Textarea
	$textarea = $_POST['_textarea'][ $post_id ];
	if( ! empty( $textarea ) ) {
		update_post_meta( $post_id, '_textarea', esc_attr( $textarea ) );
	}
	
	// Select
	$select = $_POST['_select'][ $post_id ];
	if( ! empty( $select ) ) {
		update_post_meta( $post_id, '_select', esc_attr( $select ) );
	}
	
	// Checkbox
	$checkbox = isset( $_POST['_checkbox'][ $post_id ] ) ? 'yes' : 'no';
	update_post_meta( $post_id, '_checkbox', $checkbox );
	
	// Hidden field
	$hidden = $_POST['_hidden_field'][ $post_id ];
	if( ! empty( $hidden ) ) {
		update_post_meta( $post_id, '_hidden_field', esc_attr( $hidden ) );
	}

}

As far as I can tell, that save function has a mistaken assumption that the $post_id parameter is the key for the array that makes up the $_POST['_custom_field_name'] for the custom fields. In my testing, that's not the case - the $post_id parameter is literally the WP post ID for the product variation (which makes sense in the update_post_meta call you have in here).

e.g., where you have $text_field = $_POST['_text_field'][ $post_id ]; I think that could only possibly return a value in the rare coincidence that the $post_id happens to also be the same number as the array key - but it's not going to be the value you really want.

My working code for saving the custom variation fields (works unchanged for WC versions 2.2, 2.3, 2.4) looks like this:

function save_variation_settings_fields( $post_id ) {
  foreach ($_POST['variable_post_id'] as $k => $v) {
    if ( intval($v) == intval($post_id) ) {
      update_post_meta( $post_id, '_custom_field_name1', esc_attr( $_POST['_custom_field_name1'][$k] ) );
      update_post_meta( $post_id, '_custom_field_name2', esc_attr( $_POST['_custom_field_name2'][$k] ) );
      // etc.
    }
  }
}

Hello, for some reason the following loading for select fields doesn't pre-populate with existing field value. In my case below the empty value is always preselected when I edit a product variation.

woocommerce_wp_select( 
    array( 
        'id'          => '_product_color_select[' . $variation->ID . ']', 
        'label'       => __( 'Color Swatches', 'woocommerce' ), 
        'desc_tip'    => 'true',
        'description' => __( 'Base color for visitor filtering.', 'woocommerce' ),
        'value'       => get_post_meta( $variation->ID, '_product_color_select', true ),
        'options' => array(
            ''   => __( 'No Color', 'woocommerce' ),
            'black'   => __( 'Black', 'woocommerce' ),
            'blue'   => __( 'Blue', 'woocommerce' ),
            'brown'   => __( 'Brown', 'woocommerce' ),
            'grey'   => __( 'Grey', 'woocommerce' ),
            'green'   => __( 'Green', 'woocommerce' ),
            'orange'   => __( 'Orange', 'woocommerce' ),
            'Purple' => __( 'Purple', 'woocommerce' ),
            'red'   => __( 'Red', 'woocommerce' ),
            'tan' => __( 'Tan', 'woocommerce' ),
            'white'   => __( 'White', 'woocommerce' ),
            'yellow' => __( 'Yellow', 'woocommerce' )
            )
        )
    );

Any suggestions? I see the saved values just fine on the frontend. When I edit a product variation it just selects the first selection option from the dropdown array not the value that was previously saved.