Need to condense the following into a looping function

Question

I have the following code, which works as I need it to, however, it repeats itself over and over.

I'm relatively new to PHP and haven't grasped recursive functions yet. Which I've been told I'll need to understand as this function could potentially have many levels.

if ($_POST['parent'] == "None") {
        $parent = "";
    } else {
        $parent = $connection->real_escape_string($_POST['parent']);
    }

    if (!empty($parent)) {

        $query = $connection->query("SELECT * FROM pages WHERE filename='$parent'");        

        while($row = $query->fetch_array()) {

            $path_arr = explode('/',$row['path_to']);
            end($path_arr);
            $key = key($path_arr)-1;

            $parent1 = $path_arr[$key];

            if (!empty($parent1)) {

                $query = $connection->query("SELECT * FROM pages WHERE filename='$parent1'");

                while($row = $query->fetch_array()) {

                    $path_arr = explode('/',$row['path_to']);
                    end($path_arr);
                    $key = key($path_arr)-1;

                    $parent2 = $path_arr[$key];

                    if (!empty($parent2)) {

                        $query = $connection->query("SELECT * FROM pages WHERE filename='$parent2'");

                        while($row = $query->fetch_array()) {

                            $path_arr = explode('/',$row['path_to']);
                            end($path_arr);
                            $key = key($path_arr)-1;

                            $parent3 = $path_arr[$key];

                            if (!empty($parent3)) {

                                $query = $connection->query("SELECT * FROM pages WHERE filename='$parent3'");

                                while($row = $query->fetch_array()) {

                                    $path_arr = explode('/',$row['path_to']);
                                    end($path_arr);
                                    $key = key($path_arr)-1;

                                    $parent4 = $path_arr[$key];

                                }
                            }
                        }
                    }
                }
            }
        }       
    }

    $path_to = rtrim(ltrim($parent4.'/'.$parent3.'/'.$parent2.'/'.$parent1.'/'.$parent.'/'.$filename,'/'),'/');

As you can see there are minimal differences within the nested while loops, but I'm really not sure how to make the function loop for each level.

I was pointed to this, and while I understand what the factorial is, I still am unsure on how to refactor my code into a looping function.

Any pointers?

UPDATE

Certainly moving in the right direction of what I'm hoping to achieve with Simon André Forsberg's suggestion

However (I probably should have made this clearer in my explanation), The loop(s) determine whether a 'file' (a database entry, masquerading as a file) has a parent 'file', returns that parent 'file', then checks that parent 'file' for a parent 'file' and returns it and so on and so on until there are no more parents.

It is used to create a dynamic path directory.

like so /parent4/parent3/parent2/parent1/filename/

The line of code that follows the loops (again, I probably should have included this), is below...

$path_to = rtrim(ltrim($parent4.'/'.$parent3.'/'.$parent2.'/'.$parent1.'/'.$parent.'/'.$filename,'/'),'/');

So each level of the loop outputs to this string.

I have a feeling I may have to do this using palacsint's method of taking the working part of each loop and creating that as a function.

I may be wrong but could Simon's method output to an array? first parent in pos 0, second in pos 1, etc?

However, then the query would have to have the filename='$parent' updated to look at the last array entry.

$query = $connection->query("SELECT * FROM pages WHERE filename='$parent'");

Have I bitten off more than I can chew?

Answer 1

You seem to always end with the check: Is there another parent? Or as it can be formulated, while there is another parent, grab that parent.

Luckily for you, there are while loops.

while (!empty($parent)) {
    $query = $connection->query("SELECT * FROM pages WHERE filename='$parent'");        
    while($row = $query->fetch_array()) {
        $path_arr = explode('/',$row['path_to']);
        end($path_arr);
        $key = key($path_arr)-1;
        $parent = $path_arr[$key];
        break; // break from the inner loop that fetches each row
    }
}

This code will continue looping while there is a parent available. Note that the new parent uses the same variable as the previous one, this is an important part in making this loop work.

Other suggestions:

• Use prepared statements! It is good that you seem to sanitize your inputs by using the real_escape_string method. But prepared statements is always better. And then you wouldn't have to use the real_escape_string call.

• Since this code only gets the first result, you don't need the inner while loop and can replace it by a if instead.

  while (!empty($parent)) {
      $query = $connection->query("SELECT * FROM pages WHERE filename='$parent'");        
      if ($row = $query->fetch_array()) {
          $path_arr = explode('/',$row['path_to']);
          end($path_arr);
          $key = key($path_arr)-1;
          $parent = $path_arr[$key];
      }
  }
  

• I do have to ask though: What's the point in just grabbing the parent until there are no more parents? To store all the parents in an array, let's do like this:

  $parents = array();
  while (!empty($parent)) {
      $parents[] = $parent; // add parent to the array
      $query = $connection->query("SELECT * FROM pages WHERE filename='$parent'");        
      if ($row = $query->fetch_array()) {
          $path_arr = explode('/',$row['path_to']);
          end($path_arr);
          $key = key($path_arr)-1;
          $parent = $path_arr[$key];
      }
  }
  

Now, when this loop finishes, $parents contains all the parents that was not empty. Now you can loop through that using a foreach loop, or use it with implode or whatever you'd like :)

Answer 2

If it's a function in itself, use guard clauses to make it flatten. If it's not, extract it out to separate function and use guard clauses in that. You can invert the !empty conditions and return or continue if it's true. With that you can reduce the indentation levels from nine to six.

if ($_POST['parent'] == "None") {
    $parent = "";
} else {
    $parent = $connection->real_escape_string($_POST['parent']);
}

if (empty($parent)) {
    return;
}

$query = $connection->query("SELECT * FROM pages WHERE filename='$parent'");        

while($row = $query->fetch_array()) {
    $path_arr = explode('/',$row['path_to']);
    end($path_arr);
    $key = key($path_arr)-1;

    $parent1 = $path_arr[$key];

    if (empty($parent1)) {
        continue;
    }
    ...
}

As the second step, you could create a function for

$path_arr = explode('/', $row['path_to']);
end($path_arr);
$key = key($path_arr)-1;
$parent1 = $path_arr[$key];

For example:

function get_parent_folder($filename) {
    $path_arr = explode('/', $filename);
    end($path_arr);
    $key = key($path_arr)-1;

    $parent1 = $path_arr[$key];
    return $parent1;
}

I guess instead of the array manipulation you could use PHP's built-in filename functions here which are probably well-tested and handle corner cases better than reinvented code:

function get_parent_folder($filename) {
    $dirname = dirname($filename);
    $parent_basename = basename($dirname);
    return $parent_basename;
}

(See also: Effective Java, 2nd edition, Item 47: Know and use the libraries It's a Java book and the author mentions only the JDK's built-in libraries but I think the reasoning could be true for other libraries too.)

Usage:

$query = $connection->query("SELECT * FROM pages WHERE filename='$parent'");        
while($row = $query->fetch_array()) {
    $parent1 = get_parent_folder($row['path_to']);

    if (empty($parent1)) {
        continue;
    }

    $query = $connection->query("SELECT * FROM pages WHERE filename='$parent1'");
    while($row = $query->fetch_array()) {
        $parent2 = get_parent_folder($row['path_to']);

        if (empty($parent2)) {
            continue;
        }

        $query = $connection->query("SELECT * FROM pages WHERE filename='$parent2'");
        while($row = $query->fetch_array()) {
            $parent3 = get_parent_folder($row['path_to']);

            if (empty($parent3)) {
                continue;
            }

            $query = $connection->query("SELECT * FROM pages WHERE filename='$parent3'");

            while($row = $query->fetch_array()) {
                $parent4 = get_parent_folder($row['path_to']);

            }
        }
    }
}

After that it's easier to see the pattern and comes Simon's solution.