无法从PHP文件中查看JSON数据

Question

I am using MySQL and created 2 tables in it; Users and Activity. User table has following data:

For now I am using the above data only. I want this data to show in JSON format and then I will use it in my Android app. I have tried to convert it but I am getting the below result:

( ! ) Warning: mysqli_query() expects at least 2 parameters, 1 given in D:\xampp\htdocs\MobileApp\index.php on line 18 Call Stack #TimeMemoryFunctionLocation 10.0015134480{main}( )...\index.php:0 20.0034141920getUserName( )...\index.php:38 30.0034142272http://www.php.net/function.mysqli-query' target='_new'>mysqli_query ( )...\index.php:18

( ! ) Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in D:\xampp\htdocs\MobileApp\index.php on line 20 Call Stack #TimeMemoryFunctionLocation 10.0015134480{main}( )...\index.php:0 20.0034141920getUserName( )...\index.php:38 30.0050142240http://www.php.net/function.mysqli-fetch-array' target='_new'>mysqli_fetch_array ( )...\index.php:20

{"users":[]}

I have posted the above result in 3 steps so it can be clearly identified what mistake I am making.

Below is my PHP file:

require_once ('config.php');

function getUserName()
{
// array for json response
$response = array();
$response["users"] = array();

// Mysql select query
$result = mysqli_query("SELECT * FROM Users");

while ($row = mysqli_fetch_array($result))
{
    // temporary array to create single category
    $tmp = array();
    $tmp["Id"] = $row["Id"];
    $tmp["Name"] = $row["Name"];

    // push category to final json array
    array_push($response["Users"], $tmp);
}
// keeping response header to json
header('Content-Type: application/json');

// echoing json result
echo json_encode($response);
}

getUserName();

And my config file:

<?php 
 define("HOST","localhost");
 define("DATABASE","app");
 define("USERNAME","root");
 define("PASSWORD","");

 $con=mysqli_connect(HOST,USERNAME,PASSWORD,DATABASE);
 if(!$con){
    die("Database Connection Error: " . mysqli_connect_error());
 }
 else{
  echo "Connection successful";
 }

I am getting ‘Connection successful’ from config.

I don't know what wrong I am doing.

Answer 1

The problem comes from the way you use mysqli_query.

As said in error message mysqli_query expects two parameters. The first one will be the connection object and the second one, the query.

i.e. :

$result = mysqli_query($con, "SELECT * FROM Users");

And then, build you json data like this with json_encode() php function.

require_once ('config.php');

function getUserName()
{
    // defines global since $con not in the scope of the function variables
    global $con;

    $response = array();
    while ($row = mysqli_fetch_array($result))
    {
        // temporary array to create single category
        $tmp = array();
        $tmp["Id"] = $row["Id"];
        $tmp["Name"] = $row["Name"];

        // build response array
        $response['users'][] = $tmp;
    }

    // convert $response array to json and return it
    return json_encode($response);
}

// get function return 
$users_name = getUserName();

Hope it helps.