Codeigniter: insert form_input into sql table

I'm trying to create a system of posts and custom fields. Ex: I create the post type "Product" and then I associate it some fields: "Name", "Image", "Price"... When I create one of this fields I save into my db an input field, for example for Name I will insert something like this:

$data = array(
        'name' => $field_key,
        'id' => $field_key,
        'class' => 'form-control '.$type->type_key,
        'type' => $type->type_key,
        'data-input-type' => $type->type_key
    );
    return form_input($data);

Then when I go to create my first post "Product" I want to populate a form with my custom fields.

<form method="post" action="<?php echo site_url('admin/posts/manage').'/'.$post_id; ?>">
        <?php 
        foreach ($post_fields as $field) {
        ?>
        <div class="form-group">
            <label>
                <?php 
                echo $field->name; 
                ?>
            </label>
            <?php 
            // Here the field input
            echo $field->meta_value; 
            ?>
        </div>
        <?php
        }
        ?>
        <?php if(isset($post)){ echo $post->name;}else{echo set_value('name');} ?>
        <div class="form-group">
            <input type="submit" value="Save" name="save">
        </div>
    </form>

There's no problem since I have to create a new one. But when I have to edit my post I don't know how to load field's value for that single post, because in my form_input $data I can't put something like

$value = (isset($post)) ? $post->name : set_value($field_key);

and in the $data array

'value' => $value

Somebody have an idea on what I can do? Thank you and sorry for my elementary english.