Fetch array using both if and while doesn't work - php

Question

Basically I have 2 methods in the same class, getMovie and getGenres. They are very similar but One doesn't return what I expect.
Here's getMovie method:
public function getMovie($argType, $arg){
$movieQuery = "SELECT id,
rt_id,
imdb_id,
url,
rt_url,
type,
adult,
DATE_FORMAT(release_date, '%Y') AS year,
date_added,
title,
runtime,
budget,
revenue,
homepage,
rating,
tagline,
overview,
popularity,
image,
backdrop,
trailer
FROM movies
WHERE " . $argType . " = " . $arg;
$movieResult = $this->_query($movieQuery);
$movies = array();
if($movieResult->fetch_array(MYSQLI_ASSOC)){
while($m = $movieResult->fetch_array(MYSQLI_ASSOC)){
$movies[] = array( 'title' => $m['title'],
'duplicate' => $m['duplicate'],
'url' => $m['url'],
'rt_url' => $m['rt_url'],
'release_date' => $m['release_date'],
'date_added' => $m['date_added'],
'type' => 'movie',
'adult' => $m['adult'],
'id' => $id,
'rt_id' => $m['rt_id'],
'imdb_id' => $m['imdb_id'],
'rating' => $m['rating'],
'tagline' => $m['tagline'],
'overview' => $m['overview'],
'popularity' => $m['popularity'],
'runtime' => $m['runtime'],
'budget' => $m['budget'],
'revenue' => $m['revenue'],
'homepage' => $m['homepage'],
'image' => $m['image'],
'backdrop' => $m['backdrop'],
'trailer' => $m['trailer'] );
}
return $movies;
}
else{
return false;
}
Here's getGenres method:
public function getGenres($movieId = NULL){
$genresQuery = "";
if($movieId != NULL){
$genresQuery = "SELECT id,
name
FROM genres
WHERE id = ANY (
SELECT genre_id
FROM movie_genres
WHERE movie_id = " . $movieId . ")";
}
else{
$genresQuery = "SELECT id,
name
FROM genres";
}
$genresResult = $this->_query($genresQuery);
$genres = array();
if($genresResult->fetch_array(MYSQLI_ASSOC)){
while($genre = $genresResult->fetch_array(MYSQLI_ASSOC)){
$genres[] = array( 'id' => $genre['id'],
'name' => $genre['name'] );
}
return $genres;
}
else{
return false;
}
}
And here's how I call them:
$mov = $movie->getMovie(2207);
print_r($mov); // output: Array()
$gen = $movie->getGenres(2207);
print_r($gen); // output: Array(values inside)
Both queries do actually return expected values but getMovies method doesn't work with the if statement. It works fine if I just have while loop.
I am using if as well as while as I heard that while loop can sometimes execute even when there's not values. Is there any truth to this? If there is indeed a reason to use an if statement as well as wile loop then why doesn't it work with getMovies method?
Edit 1: I tried storing the array like so but that resulted in a memory related error:
$r = $genresResult->fetch_array(MYSQLI_ASSOC);
if($r){
while($r){
$genres[] = array( 'id' => $genre['id'],
'name' => $genre['name'] );
}
return $genres;
}

Answer 1

I am using if as well as while as I heard that while loop can sometimes execute even when there's not values. Is there any truth to this?
No, according to the php manual mysqli_result::fetch_array returns an array of strings that corresponds to the fetched row or NULL if there are no more rows in resultset.
Null is falsy so the while loop will not be entered.
Although the if statement is unnecessary if you had one you would use mysqli_result::$num_rows to check if the query returned any rows.
if($movieResult->num_rows > 0){
while($m = $movieResult->fetch_array(MYSQLI_ASSOC)){
...
}
}