Question

Hy there,

i have some tree-structured data in my sqlite-table and want to delete it recursively with php. The data looks like this:

Id    ParentId
0     -1
1     0

The function:

/**
 * Delete a category with all it's subcategories
 * 
 * @param {number} id The id of the category which should be deleted
 * @return {number} The number of categories deleted
 * @throws {Exception} Throws an exception with some description text if anything goes wrong
 */
public function deleteCategory($id) {
    static $catCnt = 0;

    Helper::log("deleteCategory: id = $id");

    try {
        // Open database-connection
        $this->openDatabase();

        // Remove all subcategories recursively
        $stmtSubs = $this->_db->prepare("SELECT Id FROM categories WHERE ParentId = :id");
        $stmtSubs->bindParam(":id", $id, PDO::PARAM_INT);
        $stmtSubs->execute();
        while ($row = $stmtSubs->fetch(PDO::FETCH_ASSOC)) {
            Helper::log("deleteCategory: call recursively to delete subcategory with id = " . $row["Id"]);
            $this->deleteCategory($row["Id"]);
        }

        // All subcategories have been removed -> Now it's time to remove the category itself
        $stmt = $this->_db->prepare("DELETE FROM Categories WHERE Id = :id");
        $stmt->bindParam(":id", $id, PDO::PARAM_INT);

        Helper::log("deleteCategory: before execution, id = $id");
        $stmt->execute();

        // The code from here on never gets executed...
        Helper::log("deleteCategory: after execution, id = $id");

        $catCnt += $stmt->rowCount();

        return $catCnt;
    } catch (Exception $ex) {
        throw new Exception("Deletion of category failed:<br>" . $ex->getMessage());
    }
}

If i call this function with parameter 0, i’m getting this output:

31.08.2012 09:39:58: deleteCategory: id = 0
31.08.2012 09:39:58: deleteCategory: call recursively to delete subcategory with id = 1
31.08.2012 09:39:58: deleteCategory: id = 1
31.08.2012 09:39:58: deleteCategory: before execution, id = 1
// Here should be the "after execution"-entry, but instead it "waits" half a minute and starts the whole execution from the beginning...
31.08.2012 09:40:28: deleteCategory: id = 0
31.08.2012 09:40:44: deleteCategory: call recursively to delete subcategory with id = 1
31.08.2012 09:40:44: deleteCategory: id = 1
31.08.2012 09:40:44: deleteCategory: before execution, id = 1

As you can see it executes just fine until it should actually delete the subcategory with id 1. The execute-command does never finish, instead it doesn’t seem to do anything for half a minute and after this it starts the whole recursion from the beginning with id 0.

After the second “try” it just returns with an internal server error (“The server encountered an internal error or misconfiguration and was unable to complete your request…”)

If i call this function with parameter 1 everything works fine because the recursion is never called.

What is happening here?

Thanks,

Mik

Answer 1

Struggled around with this like half a day, decided to post it here, posted it here, had another look at it right after posting, saw the problem:

The recursive call of “$this->openDatabase();” was the source of all evil…

Thanks 😉