我使用钩子添加了Birthday作为自定义用户元数据
我可以添加/查看以下信息：
1.用户〉配置文件部分
1.我的账户页面
1.结账页面

自定义元数据：$birthday = $current_user->user_birthdate;
我在整个数据库中寻找，“user_birthdate”，包括，“wp_users”，“wp_usermeta”，wp_postmeta”**表，但在任何地方都找不到它。

我需要弄清楚在WordPress数据库中的何处查找自定义用户元数据值

• PS：我将数据库导出为.csv并使用Excel处理数据 *
  工作代码：
• 添加到functions.php *

<?php 

// Display DOB on checkout page
add_action( 'woocommerce_before_checkout_billing_form', 'func_before_checkout_form', 10 );

function func_before_checkout_form( $checkout ) { 
    echo '<h3>Checkout Form</h3>';
    
    $current_user = wp_get_current_user();
    $birthday = $current_user->user_birthdate;
    woocommerce_form_field( 'user_birthdate', array(        
        'type'  => 'date',
        'class' => array('form-row-wide'),
        'label' => 'Birthday',             
        'required' => true, 
        'default' => $birthday, 
    ), $checkout->get_value( 'user_birthdate' ) ); 
}

// Validate New Checkout Field.
add_action( 'woocommerce_checkout_process', 'validate_user_birthdate_checkout_field' );
function validate_user_birthdate_checkout_field() {
   if ( ! $_POST['user_birthdate'] ) {
      wc_add_notice( 'Please enter your Birthdate', 'error' );
   }
    //check age
    if( isset($_POST['user_birthdate']) && ! empty($_POST['user_birthdate']) ){
        // Get customer age from birthdate
        $age = date_diff(date_create($_POST['user_birthdate']), date_create('now'))->y;

        // Checking age and display an error notice avoiding checkout (and emptying cart)
        if($age<18){
            wc_add_notice( __( "You need at least to be 18 years old, to be able to checkout." ), "error" );
            //WC()->cart->empty_cart(); // <== Empty cart (optional)
        }
    }
}

// Save Billing birthdate field value as user meta data
add_action( 'woocommerce_checkout_update_customer', 'save_account_billing_birthdate_field', 10, 2 );
function save_account_billing_birthdate_field( $customer, $data ){
    if ( isset($_POST['user_birthdate']) && ! empty($_POST['user_birthdate']) ) {
         $customer->update_meta_data( 'user_birthdate', sanitize_text_field($_POST['user_birthdate']) );
    }
}

// Add field - admin.
function add_user_birtday_field( $user ) {
    ?>
        <h3><?php _e('Birthday','woocommerce' ); ?></h3>
        <table class="form-table">
            <tr>
                <th><label for="user_birthdate"><?php _e( 'Date of Birth', 'woocommerce' ); ?></label></th>
                <td><input type="date" name="user_birthdate" value="<?php echo esc_attr( get_the_author_meta( 'user_birthdate', $user->ID )); ?>" class="regular-text" /></td>
            </tr>
        </table>
        <br />
    <?php
}
add_action( 'show_user_profile', 'add_user_birtday_field', 10, 1 );
add_action( 'edit_user_profile', 'add_user_birtday_field', 10, 1 );

// Save field - admin section
function save_user_birtday_field( $user_id ) {
    if( ! empty($_POST['user_birthdate']) ) {
        update_user_meta( $user_id, 'user_birthdate', sanitize_text_field( $_POST['user_birthdate'] ) );
    }
}
add_action( 'personal_options_update', 'save_user_birtday_field', 10, 1 );
add_action( 'edit_user_profile_update', 'save_user_birtday_field', 10, 1 );

// Add field - my account page.
function action_woocommerce_edit_account_form() {   
    woocommerce_form_field( 'user_birthdate', array(
        'type'        => 'date',
        'label'       => __( 'Birth Date', 'woocommerce' ),
        'description' => __('', 'woocommerce'),
        'placeholder' => __( 'Date of Birth', 'woocommerce' ),        
    ), get_user_meta( get_current_user_id(), 'user_birthdate', true ));
}
add_action( 'woocommerce_edit_account_form', 'action_woocommerce_edit_account_form' );

// Validate - my account page.
function action_woocommerce_save_account_details_errors( $args ){
    if ( isset($_POST['user_birthdate']) && empty($_POST['user_birthdate']) ) {
        $args->add( 'error', __( 'Please provide a birth date', 'woocommerce' ) );
    }
    //check age
    if( isset($_POST['user_birthdate']) && ! empty($_POST['user_birthdate']) ){
        // Get customer age from birthdate
        $age = date_diff(date_create($_POST['user_birthdate']), date_create('now'))->y;

        // Checking age and display an error notice avoiding checkout (and emptying cart)
        if( $age < 18 ){
            wc_add_notice( __( "You need at least to be 18 years old, to be able to checkout." ), "error" );
            //WC()->cart->empty_cart(); // <== Empty cart (optional)
        }   
    }
}
add_action( 'woocommerce_save_account_details_errors','action_woocommerce_save_account_details_errors', 10, 1 );

// Save - my account page.
function action_woocommerce_save_account_details( $user_id ) {  
    if( isset($_POST['user_birthdate']) && ! empty($_POST['user_birthdate']) ) {
        update_user_meta( $user_id, 'user_birthdate', sanitize_text_field($_POST['user_birthdate']) );
    }
}
add_action( 'woocommerce_save_account_details', 'action_woocommerce_save_account_details', 10, 1 );

• PS：我不太擅长PHP*