PHP: No database selected

Question

I've got a strange error from my WAMP (PHP 5.5.12, MySQL 5.6.17).

The main error is: No database selected. I have two database tables here:

cities: id, cities

and

events (some fields are not included here): id, eventHeader, cityID.

So, there is my code. This function displaays all the events, but in the database city is written as cityID, so I have another function that must convert cityID into city name.

public function viewEvents($conf) {

  // Connecting to DB with parameters from config file;
  $mysqli = $this->dbConnect($conf);

  // quering...
  $query = "SELECT * FROM events";
  $result = $mysqli->query($query);

  while($row = mysqli_fetch_array($result)) {
    if($row['featured'] == 1) {
      $row['header'] = '<b>' . $row['header'] . '</b>';
    }

    // Getting City Name;
    $city = self::getCity($row['id']);

    // Echoing table with results here.
    echo '';
  }
  $result->free();
  $mysqli->close();
}

This function gets no error at all and works perfect. But the next one...

And this is my getCity($id):

 public function getCity($id) {

   $conf = $this->getConf();  // Getting config data (with db access);
   $mysqli = $this->dbConnect($conf);  // connecting to MySQL;

   // I'm echoing the possible mysql connection error here;


   // Quering...
   $query = "SELECT * FROM cities WHERE id = '" . $id . "';";
   $result = $mysqli->query($query);

   // Echoing mysql query error here with die();

   $row = $result->fetch_array();
   $city = $row['city'];
   return $city;
}

So, this is dbConnect($conf){

public function dbConnect($conf) {
  $mysqli = mysqli_connect($conf['db-host'], $conf['db-usr'], $conf['db-psw'], $conf['db-name']);
  return $mysqli;
}

Despite of all my code variations I get the same error: No database selected. Is it possible, cause the first method works perfectly and they both uses the same dbConnect()?

And you have verified that $conf contains all the expected values in your second function? — C3roe
– C3roe, Commented Sep 22, 2014 at 10:36
mysqli_query("use <<database>>");, or set the database in the mysqli construct, or use SELECT <<database>>.* — ʰᵈˑ
– ʰᵈˑ, Commented Sep 22, 2014 at 10:39
Okay, that's what I get: SELECT command denied to user ''@'localhost' for table 'cities'. User described in config file has grant access to this database... The same happens while using user root — Artem Ushakov
– Artem Ushakov, Commented Sep 22, 2014 at 10:42

Alejandro Arbiza · Accepted Answer · 2014-09-23 12:59:41Z

1

In general it is a good idea to only have one connection during the request lifetime, so this might work for you:

static function dbConnect($conf)
{
    static $mysqli = null; 
    if ( $mysqli === null )
    {
        $mysqli = mysqli_connect($conf['db-host'], $conf['db-usr'], $conf['db-psw'], $conf['db-name']); 
    }
    return $mysqli; 
}

// Call this function like this:
$mysqli = self::dbConnect($conf);

Now, if you have a reliable method that returns the configuration parameters, you could even improve it like this to avoid having to pass the configuration every time. :

static function dbConnect()
{
    static $mysqli = null; 

    if ( $mysqli === null )
    {
        $conf = $this->getConf();
        $mysqli = mysqli_connect($conf['db-host'], $conf['db-usr'], $conf['db-psw'], $conf['db-name']); 
    }

    return $mysqli; 
}

// Call this function like this:
$mysqli = self::dbConnect();

This way you will always use only one connection to the database, no matter how many times you call dbConnect(). If the connection is already opened, it will return it; otherwise it will open the connection and then return it.

EDIT: About why the second connection doesn't work

In the viewEvents() function the call to getCity() uses the static version self::getCity(); while inside the getCity() function there are two calls to object methods: $this->getConf() and $this->dbConnect().

I would suggest to change the call from self::getCity() to $this->getCity() inside the viewEvents() function.

edited Sep 23, 2014 at 12:59

answered Sep 22, 2014 at 13:13

Alejandro Arbiza

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2 Comments

Artem Ushakov Over a year ago

This solution works perfectly, appreciated! But I am still clueless why the second method does not want to connect :( Maybe I should consider reinstalling WAMP server...

Alejandro Arbiza Over a year ago

Oh wait! Take a look at the way you call getCity: self::getCity(). This is the static call to a class method, but then inside the method you are using $this->getConf() and $this->dbConnect(). Try changing self::getCity() for $this->getCity()

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