how to insert json to mysql database with codeigniter

Send an object with value of your data(as JSON) to your Controller. e.g (with JQuery):

$.post('your_action_url', {sendData: JSON.stringify(yourData)}, function(res) {
    console.log(res);
}, "json");

Then in your controller, you can get the Data with this CI method:

$data = json_decode($this->input->post('sendData'));

and if the $data is an Array of objects and you want to filter the $data, you can loop the $data then call the save method in your model

    $this->db->trans_begin();
    foreach($data as $row) {
        $filter_data = array(
            "id_buku" => $row->id_buku,
            "jumlah" => $row->jumlah,
            "subtotal" => $row->subtotal
        );
       //Call the save method
       $this->your_model_alias->save_as_new($filter_data);
    }

    if ($this->db->trans_status() === FALSE) {
        $this->db->trans_rollback();
        echo json_encode("Failed to Save Data");
    } else {
        $this->db->trans_commit();
        echo json_encode("Success!");
    }

Consider to use a transaction to store a lot of data at once. This is necessary to avoid things that are not desirable.

your Model's save method should be like this :

public function save_as_new($data) {
    $this->db->insert('your_table_name', $data);
}