Why is my mysqli::query() failing with a 'Couldn't fetch mysqli' Database Connection Error?

Mysqli::query(): Database Connection Error

The "mysqli::query(): Couldn't fetch mysqli" error typically indicates a problem with the database connection. The following steps describe the issue and provide a solution based on the provided code snippet:

1. Connection: In the connection file, the @ symbol in new mysqli() is used to suppress error reporting. While this is meant to prevent error display, it's better to handle errors properly instead of ignoring them.
2. Closing: In the class constructor, you assign $DBConnect to a class member variable. This ensures that the connection object is available throughout the class. However, in the __destruct() method, you close the connection if there is no connection error. This is an issue because subsequent queries would fail as the connection is no longer available.
3. Reopening: The __wakeup() method is intended to reopen the connection after serialization. However, it is not invoked when the class is instantiated, which means that the connection remains closed.

Solution:

1. Remove the @ symbol from the connection object instantiation. Handle errors in a more robust manner.
2. Move the connection closing code to a separate method and call it only when it's necessary to close the connection.
3. Ensure that the __wakeup() method is invoked when the class is instantiated (e.g., when retrieving an object from a session).

Modified Code:

// Connection file
$DBConnect = new mysqli("localhost", "root@localhost", NULL, "Ladle");

// Check for connection error
if ($DBConnect->connect_errno) {
    $ErrorMsgs[] = "The database server is not available. Connect Error is " . $DBConnect->connect_errno . " " . $DBConnect->connect_error . ".";
}

// Class
class EventCalendar {
    private $DBConnect = NULL;

    function __construct() {
        include("inc_LadleDB.php");
        $this->DBConnect = $DBConnect;
    }

    function __destruct() {
        // Close the connection only if it's not closed already
        if (!$this->DBConnect->connect_error) {
            $this->DBConnect->close();
        }
    }

    function __wakeup() {
        // Include the database connection data
        include("inc_LadleDB.php");
        $this->DBConnect = $DBConnect;
    }
    
    // Event adding method
    // ...
}

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