PHP Class Database Connection Scope Issue

Question

For a new project that I'm doing in PHP I've created an SQLMethods class to connect to the database and perform queries. Tonight was the first night that I actually got to test it (I wrote it a week or so ago and forgot about it) and an unexpected error occured: When it was calling my ExecuteQuery() function, it wouldn't use the database I selected in the constructor.

The constructor:

 public function SQLMethods() {
  $SQLConnection = mysql_connect($SQLDBAddress, $SQLUserName, $SQLPassword);

  if (!$SQLConnection) {
   die('Could not connect: ' . mysql_error());
  }

  mysql_select_db($SQLDB, $SQLConnection);
 }

The function in question:

 public function ExecuteQuery($Query) {
  mysql_query($Query, $SQLConnection) or die('Could not perform query: ' . mysql_error());
 }

Does anyone see what the issue might be? Does the connection close after the constructor completes?

Answer 1

you should declare $SQLConnection in your class, and you should refer to it as

 $this->SQLConnection

and not simply $SQLConnection.

Answer 2

$SQLConnection doesn't exist within the ExecuteQuery method, you need to either pass it as a parameter, or add it as a class-property in the contructor and access with $this->sqlConnection elsewhere.

Answer 3

The variable $SQLConnection ExecuteQuery() is trying to use is created within another scope. (The SQLMethods function).

The connection closes when the PHP script has done its work or if you close it yourself (if the connection is made within that script)

You should skip the $SQLConnection variable within ExecuteQuery as stated by the php.net documentation

"If the link identifier is not specified, the last link opened by mysql_connect() is assumed."