Run PHP query through function

Question

I have this php function

function showfeed($query_){
    $query = $con->query($query_);
          while ($row=$query->fetch_row()) {
         ...
  }

And this is how i run this function

showfeed("SELECT * FROM uploads WHERE uploads.username = '$NameId' OR uploads.username IN(
        SELECT username FROM followers  WHERE uploads.username = followers.following)ORDER BY `Date` DESC LIMIT 0,100");

But when i try to run that function i get this error

Call to a member function query() on null

Where do you define `$con`? (According to the error, it's null. So you're not creating it correctly.) — David, Oct 11 '16 at 18:05
No, no you shouldn't. Sprinkling the `global` keyword haphazardly any time there's an error is going to cause more problems than it solves. — David, Oct 11 '16 at 18:07
There isn't enough context in the code here to know for certain. Maybe it should be supplied to the function? Maybe it should be a class-level member? Maybe it should be created and destroyed entirely within the scope of that function? There are multiple options. — David, Oct 11 '16 at 18:10

Mulan · Accepted Answer · 2016-10-11T18:16:36.730

$con is not defined in the showFeed function's scope.

You should pass $con as an argument to the function

function showFeed($con, $query) {
  $query = $con->query($query);
  ...
}

Or use a global variable

function showFeed($query)
  global $con;
  $query = $con->query($query);
  ...
}

Warning: depending on global variables a lot will make your program really, really bad. You should try to avoid globals as much as possible.

However, in the case of singletons (such as your database connection $con), it is common to use globals. A common workaround is to use a singleton class that might look like this

class Db {
  static private $con;
  static connection() {
    // if no connection exists
    if (!self::$con)
      // store a reference to a new connection here
      // mysqli_connect is an example here; your code might differ for creating $con
      self::$con = mysqli_connect(...);
    // return the connection reference
    return self::$con;
  }
}

Now, because PHP will always allow you to reference the Db class in any function (in the same namespace), you don't have to use the global variables anymore

function showFeed($query) {
  $query = Db::connection()->query($query);
}

In which case it might make sense to make query a static method for your Db class too!

class Db {
  static private $con;
  static public connection() {
    if (!self::$con)
      self::$con = mysqli_connect(...);
    return self::$con;
  }
  static public query($query) {
    // we can get the connection from ourself!
    return self::connection()->query($query)
  }
}

Now your function can be simplified

function showFeed($query) {
  $query = Db::query($query);
}

Of course, you don't want to go overboard with this. I don't know what $con is in your particular example – whatever library/adapter you're using might have some of these things built in. These are just here as examples that help you think about the problem differently.

Thanks,that was a silly mistake – J.Doe Oct 11 '16 at 18:07 — J.Doe, Oct 11 '16 at 18:07

score 0 · Answer 2 · answered Oct 11 '16 at 18:06

0

This is because $con doesn't have scope in your function, you would need to either pass it in or make its scope visible through your class I.e $this->conn.

answered Oct 11 '16 at 18:06

Ryan

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Run PHP query through function

2 Answers2