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Class Variable Declaration

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BACKGROUND:  I am now running with PHP 5.5.38, and things are nearly back to normal.  My error messages have returned, and things that once worked, now function well again.  This said, I wish to make good on the pain and disappointment that I suffered and am requesting your help to do so.

REQUEST:  Please find below a PHP class that I created in order to gather data from my database.  It works fine in my current PHP environment and produces the expected results.  It has been upgraded to handle multiple languages and editions of the same letter number.  In addition, I have included a list of suspect variables -- namely, variables whose undeclared status may have been a source of difficulty while running in my previous PHP 5.6.33 environment.

class Newsletter {
    public $letter_no;
    public $letter_lang;
    public $mysqli_obj;
    public $letter_ed;
    public $pc_total;
    public $podcasts;

    public function __construct($letter_no, $letter_lang, $mysqli_obj, $letter_ed = 1) {
        $this->letter_no = $letter_no;
        $this->letter_lang = $letter_lang;
        $this->mysqli_obj = $mysqli_obj;
        $this->letter_ed = $letter_ed;
    }

    public function get_letter_data() {
        $sql = "SELECT letter.*, qa.*
                FROM sevengates_letter AS letter
                JOIN sevengates_qa AS qa
                    ON letter.letter_no = qa.letter_no
                    WHERE letter.letter_no = ? AND letter.letter_lang = ?
                    ORDER BY letter.letter_ed DESC";
        $mysqli_stmt = $this->mysqli_obj->stmt_init();
        $mysqli_stmt->prepare($sql);
        $mysqli_stmt->bind_param('is', $this->letter_no, $this->letter_lang);
        $mysqli_stmt->execute();
        $meta = $mysqli_stmt->result_metadata();
        while ($field = $meta->fetch_field()) {
            $params[] = &$row[$field->name];
        }
        call_user_func_array(array($mysqli_stmt, 'bind_result'), $params);
        while ($mysqli_stmt->fetch()) {
            foreach($row as $key => $val) {
                $c[$key] = $val;
            }
            $prelim_result[] = $c;
        }
        foreach ($prelim_result as $arr) {
            foreach ($arr as $name => $value){
                $letter_results[$name] = $value;
            }
        }
        return $letter_results;
    }

    public function get_nextletter_data() {
        $next_letter_no = $this->letter_no + 1;
        $sql = "SELECT letter_no, letter_title, letter_abstract FROM sevengates_letter WHERE letter_no = ?";
        $mysqli_stmt = $this->mysqli_obj->stmt_init();
        $mysqli_stmt->prepare($sql);
        $mysqli_stmt->bind_param('i', $next_letter_no);
        $mysqli_stmt->execute();
        $meta = $mysqli_stmt->result_metadata();
        while ($field = $meta->fetch_field()) {
            $params[] = &$row[$field->name];
        }
        call_user_func_array(array($mysqli_stmt, 'bind_result'), $params);
        while ($mysqli_stmt->fetch()) {
            foreach($row as $key => $val) {
                $c[$key] = $val;
            }
            $prelim_result[] = $c;
        }
        $mysqli_stmt->free_result();
        foreach ($prelim_result as $arr) {
            foreach ($arr as $name => $value){
                $nextletter_results[$name] = $value;
            }
        }
        return $nextletter_results;
    }

    public function get_podcasts() {
        $sql = "SELECT podcast_ref FROM sevengates_podref WHERE letter_no = ?";
        $mysqli_stmt = $this->mysqli_obj->stmt_init();
        $mysqli_stmt->prepare($sql);
        $mysqli_stmt->bind_param('i', $this->letter_no);
        $mysqli_stmt->execute();
        $meta = $mysqli_stmt->result_metadata();
        while ($field = $meta->fetch_field()) {
            $params[] = &$row[$field->name];
        }
        call_user_func_array(array($mysqli_stmt, 'bind_result'), $params);
        while ($mysqli_stmt->fetch()) {
            foreach($row as $key => $val) {
                $c[$key] = $val;
            }
            $prelim_result[] = $c;
        }
        $i = 1;
        foreach ($prelim_result as $arr) {
            foreach ($arr as $name => $value) {
                $name = $name . '_' . $i;
                $podcasts[$name] = $value;
            }
            $i++;
        }
        $this->pc_total = count($podcasts);
        return $podcasts;
    }

    public function get_podcasts_data($podcasts) {
        $this->podcasts = $podcasts;
        $prelim_result = [];
        $c = [];
        $row = [];
        $podcast_results = [];
        foreach ($podcasts as $name => $value) {
            $params = [];
            $mysqli_stmt = $this->mysqli_obj->stmt_init();
            $sql = "SELECT item_podtype, podcast_no_item, item_title, item_description, item_guid FROM rss2_podcast_item WHERE podcast_no_item = ?";
            $mysqli_stmt->prepare($sql);
            $mysqli_stmt->bind_param('i', $value);
            $mysqli_stmt->execute();
            $meta = $mysqli_stmt->result_metadata();
            while ($field = $meta->fetch_field()) {
                $params[] = &$row[$field->name];
            }
            call_user_func_array(array($mysqli_stmt, 'bind_result'), $params);
            while ($mysqli_stmt->fetch()) {
                foreach($row as $key => $val) {
                    $c[$key] = $val;
                }
            }
            $prelim_result[] = $c;
            $mysqli_stmt->free_result();
        }
        foreach ($prelim_result as $arr) {
            foreach ($arr as $name => $value){
                $pc_result[$name] = $value;
            }
            $podcast_results[] = $pc_result;
        }
        return $podcast_results;
    }
    public function get_pc_total() {
        return $this->pc_total;
    }
}

LIST OF SUSPECT VARIABLES

$params = [];
$prelim_result = [];
$c = [];
$letter_results = [];
$next_letter_results = [];
$row = [];
$podcast_results = [];

DISCUSSION

I feel fairly comfortable with handling certain kinds of variables, but very uncomfortable handling others.  In fact, I am not at all sure why the above class works, as it took  a lot of guess work to make it function.  Guess work is inefficient.

QUESTION:  How does one properly declare class variables that are not related to the arguments of the constructor function?  Please provide examples from the list and code provided.

Roddy

 

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If it's an actual class property variable then you declare those before the constructor along with their visibility - public, protected, or private.  If you're talking about variables that you just use locally in some function, you treat them like any other variable in any other piece of code.

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Seems odd to me that you declare all of the instance variables as public. It is more normal to make them private.

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Quote

... you treat them like any other variable in any other piece of code.

JSG:  Please select one of any of the provided class functions that contain "ordinary variables" and show me how you would declare them in the context of the class provided. 

davej:  Why would you make the private and not public?

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Please select one of any of the provided class functions that contain "ordinary variables" and show me how you would declare them in the context of the class provided.

You don't have to declare variables in PHP, at least not like you do in other languages where you declare a variable as a certain type before you use it.  PHP variables only need a value if you're using them, so you can either initialize them with an initial value, like an empty array if the variable is going to be an array, or just set them to their value to start with before you refer to them elsewhere.  The only way that PHP really has to declare a variable is with the class properties.

On another note, you use a lot of code to do some simple stuff here.  One issue is that you keep referring to a variable called $row that doesn't exist.  Another issue is that it looks like you have several lines of code which include multiple loops and calls to result_metadata, fetch_field, call_user_func_array, etc, which can all be replaced by a single call to fetch_all.  I don't see why you're doing it the long way when there's a single function to do that.  It seems unnecessarily complex and time-consuming.  

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JSG:  For someone who is always asking for code, you are very reluctant to provide it. A simple example in the context of the class provided would be extremely helpful.

Roddy

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JSG:  I have never used the fetch_all( ) method in this context -- only the fetch_assoc( ) method --, and it does not work in the context provided.

Roddy

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For someone who is always asking for code, you are very reluctant to provide it. A simple example in the context of the class provided would be extremely helpful.

I don't know what you're asking for.  Like I said, variables do not get declared in PHP, only defined and used, and I don't see any issues in your code other than what I described above.  The only edit I would make would be to remove the loops and fetch the result set all at once with the built-in methods.  e.g.:

$sql = "SELECT letter_no, letter_title, letter_abstract FROM sevengates_letter WHERE letter_no = ?";
$mysqli_stmt = $this->mysqli_obj->stmt_init();
$mysqli_stmt->prepare($sql);
$mysqli_stmt->bind_param('i', $next_letter_no);
$mysqli_stmt->execute();
$result = $mysqli_stmt->get_result();
$return = $result->fetch_all(MYSQLI_ASSOC);

Now $return has the entire result set, organized as an associative array.  You don't need to use a single loop.  Although it would be good practice to add error checking to that code as well.

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4 hours ago, iwato said:

Davej:  Why would you make the private and not public?

Instance variables are usually declared as private because OOP considers "encapsulation" to be a good thing. This is the same reasoning behind minimizing the number of global variables. If some variable does not need to be public or global then it shouldn't be. In your example the constructor sets the values of the instance variables, so they themselves don't need to be public.

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Unfortunately, the following did not work.

$sql = "SELECT letter_no, letter_title, letter_abstract FROM sevengates_letter WHERE letter_no = ?";
$mysqli_stmt = $this->mysqli_obj->stmt_init();
$mysqli_stmt->prepare($sql);
$mysqli_stmt->bind_param('i', $next_letter_no);
$mysqli_stmt->execute();
$result = $mysqli_stmt->get_result();
$return = $result->fetch_all(MYSQLI_ASSOC);

I have set it aside, however, for future consideration.  I simple have no more time, if I am to meet my spring deadline for the commencement of podcast production.  I have only two major tasks left -- both of which I suspect will be far smaller than they appear daunting.  Thanks to you and others I now feel confident that I will be able to avoid many of the pitfalls into which I have fallen along the way.  Have a great week!

Roddy

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