php – 保存选择字段的(多个)元值

(...)


    <select style="width:100%" id="_receita" name="_receita[]" multiple="multiple" data-placeholder="<?php _e( 'Search for a product','woocommerce' ); ?>">
            <?php
                echo '<option value="TEST"> TEST </option>';
                echo '<option value="TEST1"> TEST1 </option>';
                echo '<option value="TEST2"> TEST2 </option>';
                ?>
            </select>

    // few others custom fields:
   <?php $ingrediente_x_quantidade = get_post_meta( $post->ID,'_ingrediente_x_quantidade',true ); ?>  
            <input placeholder="<?php _e( 'Ingrediente','woocommerce' ); ?>" type="text" class="ingrediente" id ="_ingrediente" name="_ingrediente" value="<?php echo $ingrediente_x_quantidade[0]; ?>" style="width: 90%;" />
            <input placeholder="<?php _e( 'qnt.','woocommerce' ); ?>" type="number" name="_quantidade" id="_quantidade" class = "quantidade" value="<?php echo $ingrediente_x_quantidade[1]; ?>" step="any" min="0" style="width: 25%;" />

(...)

为了保存数据,我在function.php中包括：

add_action( 'woocommerce_product_options_general_product_data','woo_add_custom_general_fields' );
    // Save Fields
    add_action( 'woocommerce_process_product_meta','woo_add_custom_general_fields_save' );


function woo_add_custom_general_fields_save( $post_id ){

// Custom Field
 $ingrediente_x_quantidade =  array( esc_attr( $_POST['_ingrediente'] ),esc_attr( $_POST['_quantidade'] ) );
 update_post_meta( $post_id,$ingrediente_x_quantidade );

 // Select Field
 foreach ($_POST["_receita"] as $receita) {
 update_post_meta($post->ID,"_receita",$receita);
        }

        }

我正在为自定义字段(“_ingrediente_x_quantidade”)获得一切正常,但对于选择字段,“_ renita”我得到一个空数组：

[_ingrediente_x_quantidade] => Array
(
[0] => a:2:{i:0;s:19:”Aveia,flocos,crua”;i:1;s:3:”113″;}
)

[_receita] => Array
(
[0] =>
)

我做错了什么？我很擅长编码！