ver

<script>
    $(document).ready(function(){
        $("#submit").click(function(e){
            e.preventDefault();
            product_name = $("#product_name").val();
            color = $("#colorWell").val();
            $.ajax({
                type:"POST",
                data:{"product_name":product_name, "color":color},
                url:"<?php echo base_url(); ?>admin/products",
                success:function(data){
                    alert(data);
                }
            });
        });
    });
</script>

<input type="text" class="form-control" id="product_name" name="product_name">
<input type="color" id="colorWell" name="color">
<input type="file" id="product_image" name="product_image[]" multiple>
<input type="submit" class="btn btn-primary" id="submit" name="submit">

controlador

public function products()
{
    $product_name = $this->input->post('product_name');
    $color = $this->input->post('color');

    $dataInfo = array();
    $files = $_FILES;
    $cpt = count($_FILES['product_image']['name']);
    for($i=0; $i<$cpt; $i++)
    {           
        $_FILES['product_image']['name']= $files['product_image']['name'][$i];
        $_FILES['product_image']['type']= $files['product_image']['type'][$i];
        $_FILES['product_image']['tmp_name']= $files['product_image']['tmp_name'][$i];
        $_FILES['product_image']['error']= $files['product_image']['error'][$i];
        $_FILES['product_image']['size']= $files['product_image']['size'][$i];    

        $this->upload->initialize($this->set_upload_options());
        $this->upload->do_upload();
        $dataInfo[] = $this->upload->data();
    }
    $data = array(
            'product_name' => $product_name,
            'color' => $color,
            'product_image' => implode(",",$dataInfo['product_image']),
        );
    $result_set = $this->db->insert('add_product',$data);
    if($sql == true)
    {
        echo 'New Product Added';
    }
    else
    {
        echo 'Unable to Proceed!';
    }
}

private function set_upload_options()
{   
    $config = array();
    $config['upload_path'] = ''.base_url().'resource/product/';
    $config['allowed_types'] = 'gif|jpg|png';
    $config['max_size']      = '0';
    $config['overwrite']     = FALSE;
    return $config;
}

En este código estoy tratando de insertar y quiero mover una imagen a una carpeta. Pero ahora, el problema es que cuando hago clic en el botón Enviar aparece un error como se muestra a continuación:

Message: Undefined index: product_image

y aspecto de consulta:

INSERT INTO `product` (`product_name`, `color`, `product_image`) VALUES ('men hoodies','#004080', NULL)

No sé dónde estoy haciendo mal. Entonces, ¿cómo puedo resolver este problema? Por favor, ayúdame

Gracia