PHP passing ID

[Natsu123]

Hi guys, I really need your help. I am Programming an app where a teacher logs in with a username and password. After the login a new Fragment in the app opens where the Teacher see all his students in a ListView. To Login I only type the username and the password . I use for this php and mysql. My problem is that my login.php don't pass the ID from the teacher to the get_data.php where I do a SQL query. I just started with programming so please be patient.

My login.php:

<?php
        session_start();
    if($_SERVER['REQUEST_METHOD']=='POST'){

                $username = $_POST['username'];
        $password = $_POST['password']; 
                $Teacher_ID= $_GET['Teacher_ID'];


        if($username == '' || $password == ''){
            echo '';
        }else{
        require_once('dbConnect.php');

                $sql = "SELECT ID_Teacher, username, password FROM Teacher WHERE username='$username' and password='$password'";


                $check = mysqli_fetch_array(mysqli_query($con,$sql));


        }
        if(isset($check)){


            echo "succes";
        }else{
            echo "wrong username or password";
        }

    }else{
        echo "error try again";
    }

My get_data.php:

<?php
session_start();
require_once('dbConnect.php');
$_GET['Lehrer_ID'] = $id;


$sql = "SELECT Student.Name,Student.Surname FROM Student WHERE Student.ID_Teacher = .$id";

$res = mysqli_query($con,$sql);
$result = array();

while($row = mysqli_fetch_array($res))
{

array_push($result,
array('Name'=>$row[0], 'Surname'=>$row[1]));
}

echo json_encode(array("result"=>$result));
mysqli_close($con);

?>

$_GET['Lehrer_ID'] = $id;

Is the wrong way around, should be?

$id = $_GET['Lehrer_ID'];

Anyhow, you should store the logged in user_id in a session variable, e.g. $_SESSION['id']

Be aware that your current code leaves you wide open to SQL injection as you are not sanitizing your user input variables ($_POST) neither are you using prepared statements.

See my recent tute: DW Tutorial: Common Issues with MySQL and PHP

[Natsu123]

login.php -->So instead of

$Teacher_ID= $_GET['Teacher_ID']; 

should I write ?

$_SESSION['Teacher_ID'];

But what should I write in get_data.php do get the ID from the Teacher from login.php?

There are quite a few things with this script that require attention:

You place unsanitized user input vars directly in the SQL (open to SQL injection) - see see my tutorial (link in previous post) for a section on this (#2. SQL Injection: What to do with $_POST and $_GET variables):

 $sql = "SELECT ID_Teacher, username, password FROM Teacher WHERE username='$username' and password='$password'";

The password field is plaintext not hashed. This is very dangerous. Have a look at the password_verify() and password_hash() functions - or see my tutorial for a section on this (#11. Storing and Retrieving Authentication Data).

On this...

 if(isset($check)){
            echo "succes";

Add the user id to the session superglobal array ($_SESSION):

if(isset($check)){
            echo "succes";
            $_SESSION['id'] = $check['ID_Teacher'];

The logged in teacher is now safely entered (via ID) in the session. So now you can have something like:

$sql = "SELECT Student.Name,Student.Surname FROM Student WHERE Student.ID_Teacher = {$_SESSION['id']}";

(Not sure where you were getting $_GET from). Although, when dynamic data is inserted into a statement, I always use a prepared statement rather than a query. See tutorial (#4. What to do With Dynamic Values?)

[Natsu123]

Thx man :) when I check with var_dump($_SESSION['id']); in my login.php data it gives me back the ID from the Teacher. But unfortunately when I check it on get_data.php then it seems to be that it don't recieve the ID. I post my get_data.php maybe I did something wrong. I will change the code later and secure it agains sql injection.

<?php
    session_start();
    require_once('dbConnect.php');
    $_SESSION['id'] = $check['ID_Lehrer'];
    $sql = "SELECT Student.Name,Student.Surname FROM Student WHERE Student.ID_Teacher = {$_SESSION['id']}";
    $res = mysqli_query($con,$sql);
    $result = array();
    while($row = mysqli_fetch_array($res))
    {
    array_push($result,
    array('Name'=>$row[0], 'Surname'=>$row[1]));
    }
    echo json_encode(array("result"=>$result));
    mysqli_close($con);
    ?>

Why $_SESSION['id'] = $check['ID_Lehrer']; in this page? You should have done that already in the login page. $check['ID_Lehrer'] does not exist in this page. Just take out line 4.

[Natsu123]

I already tried this. But then I get an error

<br/>
<b>Warning</b>: mysqli_fetch_array() excepts parameter 1
to be mysli_result, boolean given in <b>/home/u88870/
public_html/get_data.php</b> on line<b>10</b>

which means it is this line while($row = mysqli_fetch_array($res)) but I don't get why? Do you have an idea?

Mean $res is not a resource. Your query failed and returned 'false'. Could be a number of things. Do a die() to find out:

$res = mysqli_query($con, $sql) or die(mysql_error());
while($row = mysql_fetch_array($res))
{
   ...
}

[Natsu123]

I checked it and the problem is that the get__data.php file is not getting the ID. In the query it shows NULL. That is the reason why it returns false. Did I start the session wrong or forgot something?

Show the updated code for both pages.

[Natsu123]

login.php

<?php
        session_start();
        if($_SERVER['REQUEST_METHOD']=='POST'){

         $username = $_POST['username'];
         $password = $_POST['password'];       

        if($username == '' || $password == ''){
            echo '';
        }else{
        require_once('dbConnect.php');

        $sql = "SELECT ID_Lehrer, username, password FROM Lehrer WHERE username='$username' and password='$password'";

        echo mysql_error();

        $check = mysqli_fetch_array(mysqli_query($con,$sql));                    
        }
        if(isset($check)){

            echo "success";
            $_SESSION['id'] = $check['ID_Lehrer'];

        }else{
            echo "Wrong Password or Username";
        }

        }else{
            echo "Error, try again!";
    }
    ?>

get_data.php

<?php

session_start();

require_once('dbConnect.php');

$sql = "SELECT Student.Name,Student.Surname FROM Student WHERE Student.ID_Teacher = {$_SESSION['id']}";

$res = mysqli_query($con,$sql);

$result = array();

while($row = mysqli_fetch_array($res))  
{  
array_push($result, array('Name'=>$row[0], 'Surname'=>$row[1]));  
}

echo json_encode(array("result"=>$result));

mysqli_close($con);

?>

Are you getting 'succes' from the login script? As long as every page you go to before get_data has a session_start() then the 'id' will be stored in the session.

[Natsu123]

No I don't get the echo "success" but I can still login but I remember that that in the past it appeared when I logged in. I will check it. Do you think that it could be the reason?

If you are not logging in and getting the 'success' message, then you are not logging in - from your code, you are not entering the successful branch of your conditional construct:

if(isset($check)){
        echo "success";
        $_SESSION['id'] = $check['ID_Lehrer'];
    }else{
        echo "Wrong Password or Username";
    }

Which msg are you getting?
Try if($check) instead of if(isset($check))

[Natsu123]

No that doesn't change anything. I rember now why it didn't appear because I made it not to appear on the screen in my java code. Maybe there is something wrong with my java code.

ActivityLogin.java

public class ActivityLogin extends AppCompatActivity implements View.OnClickListener{

    public static final String USER_NAME = "USER_NAME";

    public static final String PASSWORD = "PASSWORD";

    private static final String LOGIN_URL = "http://baxxxxxx.16mb.com/login.php";

    private EditText editTextUserName;
    private EditText editTextPassword;

    private Button buttonLogin;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_activity_login);

        editTextUserName = (EditText) findViewById(R.id.username);
        editTextPassword = (EditText) findViewById(R.id.password);

        buttonLogin = (Button) findViewById(R.id.buttonUserLogin);

        buttonLogin.setOnClickListener(this);
    }


    private void login(){
        String username = editTextUserName.getText().toString().trim();
        String password = editTextPassword.getText().toString().trim();
        userLogin(username,password);
    }

    private void userLogin(final String username, final String password){
        class UserLoginClass extends AsyncTask<String,Void,String> {
            ProgressDialog loading;
            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                loading = ProgressDialog.show(ActivityLogin.this,"Please Wait",null,true,true);
            }

            @Override
            protected void onPostExecute(String s) {
                super.onPostExecute(s);
                loading.dismiss();
                if(s.equalsIgnoreCase("success")){
                    Intent intent = new Intent(ActivityLogin.this,ListView.class);
                    intent.putExtra(USER_NAME,username);
                    startActivity(intent);
                }else{
                    Toast.makeText(ActivityLogin.this, s, Toast.LENGTH_LONG).show();
                }
            }

            @Override
            protected String doInBackground(String... params) {
                HashMap<String,String> data = new HashMap<>();
                data.put("username",params[0]);
                data.put("password",params[1]);

                RegisterUserClass ruc = new RegisterUserClass();

                String result = ruc.sendPostRequest(LOGIN_URL,data);

                return result;
            }
        }
        UserLoginClass ulc = new UserLoginClass();
        ulc.execute(username,password);
    }

    @Override
    public void onClick(View v) {
        if(v == buttonLogin){
            login();
        }
    }
}

ListView.java

public class ListView extends ActionBarActivity implements View.OnClickListener {

    private TextView textViewJSON;
    private Button buttonGet;
    private Button buttonParse;
    private TextView textView;

    public static final String MY_JSON ="MY_JSON";

    private static final String JSON_URL = "http://www.baxxxxxxx.16mb.com/get_data.php";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textViewJSON = (TextView) findViewById(R.id.textViewJSON);
        textViewJSON.setMovementMethod(new ScrollingMovementMethod());
        buttonGet = (Button) findViewById(R.id.buttonGet);
        buttonParse = (Button) findViewById(R.id.buttonParse);
        buttonGet.setOnClickListener(this);
        buttonParse.setOnClickListener(this);

        textView = (TextView) findViewById(R.id.textViewUserName);

        Intent intent = getIntent();

        String username = intent.getStringExtra(ActivityLogin.USER_NAME);

        textView.setText("Willkommen Dr. " + username);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onClick(View v) {
        if(v==buttonGet){
            getJSON(JSON_URL);
        }

        if(v==buttonParse){
            showParseActivity();
        }
    }

    private void showParseActivity() {
        Intent intent = new Intent(this, ParseJSON.class);
        intent.putExtra(MY_JSON,textViewJSON.getText().toString());
        startActivity(intent);
    }


    private void getJSON(String url) {
        class GetJSON extends AsyncTask<String, Void, String>{
            ProgressDialog loading;

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                loading = ProgressDialog.show(ListView.this, "Please Wait...",null,true,true);
            }

            @Override
            protected String doInBackground(String... params) {

                String uri = params[0];

                BufferedReader bufferedReader = null;
                try {
                    URL url = new URL(uri);
                    HttpURLConnection con = (HttpURLConnection) url.openConnection();
                    StringBuilder sb = new StringBuilder();

                    bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));

                    String json;
                    while((json = bufferedReader.readLine())!= null){
                            sb.append(json+"\n");
                    }

                    return sb.toString().trim();

                }catch(Exception e){
                    return null;
                }

            }

            @Override
            protected void onPostExecute(String s) {
                super.onPostExecute(s);
                loading.dismiss();
                textViewJSON.setText(s);
            }
        }
        GetJSON gj = new GetJSON();
        gj.execute(url);
    }
}

Not my scene. Anybody else?

[Natsu123]

Do I have to work with JOINS ?? Would that solve the problem?