php - codeigniter : inserting data/record into 2 tables -

i have 2 tables 'pengguna' , 'mahasiswa' , 1 have form 1 form inserting 2 tables, far manage insert data when has "primary key" , "foreign key" has problem, u can see code below id_pengguna table pengguna primary key , id_pengguna table mahasiswa foreign key problem when inserting data, id_pengguna pengguna has value while in table mahasiswa has no value, below code, there simple way or doing wrong?

pengguna table mahasiswa table

controller

public function insertmahasiswa(){     $username = $this->input->post('username');     $password = md5($this->input->post('password'));     $data1 = array(             'username'=>$username,             'password'=>$password,             'level'=>3,         );     $nim = $this->input->post('nim');     $nama = $this->input->post('nama');     $email = $this->input->post('email');     $telepon = $this->input->post('telepon');     $data = array(             'nim'=>$nim,             'nama_mahasiswa'=>$nama,             'email'=>$email,             'telepon'=>$telepon,         );     $insert = $this->mmahasiswa->create('pengguna',$data1);     $insert1 = $this->mmahasiswa->create('mahasiswa',$data);     redirect(site_url('mahasiswa/data?balasan=1')); } 

model

function create($table,$data){     $query = $this->db->insert($table, $data);     return $query; } 

you need return last insert id form model file

in model

function create($table,$data){     $query = $this->db->insert($table, $data);     return $this->db->insert_id();// return last insert id } 

in controller

$id_pengguna = $this->mmahasiswa->create('pengguna',$data1);     $data = array(                 'nim'=>$nim,                 'nama_mahasiswa'=>$nama,                 'email'=>$email,                 'telepon'=>$telepon,                 'id_pengguna'=>$id_pengguna// add last insert id mahasiswa table             );         $insert1 = $this->mmahasiswa->create('mahasiswa',$data);