public function login(Request $request) {

    $assistant = DB::table('assistants')
        ->where('username', $request->input('username'))
        ->where('mot_de_passe', $request->input('mot_de_passe'))
        ->first();


    if($assistant != null){

        return response()->json ($assistant);
    }else{
        $returnData = array(
            'status' => 'false',
            'message' => 'write some message..');
        return response()->json ($returnData ,500  );
    }}

IAssistant iAssistant= APIClient.getClient().create(IAssistant.class);


              iAssistant.login(username.getText().toString(),password.getText().toString()).enqueue(new Callback<Assistant>() {
                @Override
                public void onResponse(retrofit2.Call<Assistant> call, Response<Assistant> response) {

                if (response.isSuccessful()){
                        startActivity(new Intent(getApplicationContext(), BottomNavigation.class));
                    Toast.makeText(getApplicationContext(),"assistant"+response.body().getNom(),Toast.LENGTH_LONG).show();

                 }}

                @Override
                public void onFailure(retrofit2.Call<Assistant> call, Throwable t) {

                    Toast.makeText(getApplicationContext(),"'error",Toast.LENGTH_LONG).show();
                    Log.v("tag!!!!!!!!!!","error"+t.getMessage());

                }
                });