SQL join results into an object in codeigniter

Question

ok, a bit of background,

• just into codeigniter
• not a fan of sql and server-side scripts
• i know what joins are
• i have a many-to-many database for the first time

it's because joins typically have the following example as a result. but i wanted to parse this without having to build code to ignore repetitions. it's a 3-table join sample. the issue of repeating values increases as i join more tables:

table1.authorid    table1.authorname    table2.books     table3.favorited
       1                 john           john's book 1        jean
       1                 john           john's book 1        joe
       1                 john           john's book 2        ken
       1                 john           john's book 2        mark
       2                 mark           mark's book 1        alice
       2                 mark           mark's book 1        ted
       2                 mark           mark's book 2        sarah
       2                 mark           mark's book 2        denise

is there a way in codeigniter (or plain PHP) that i can get this array form and turn it into something like json (and parse it like json)

$result = [
    {
        'authorid':1,
        'authorname':'john',
        'books':['john's book1','john's book2'],
        'favorited':['jean','joe','ken','mark']
    },
    {
        'authorid':2,
        'authorname':'mark',
        'books':['mark's book1','mark's book2'],
        'favorited':['alice','ted','sarah','denise']
    }
]

Update: this is not limited to this depth of objects/arrays (like in the example). it can go deeper (arrays in arrays, arrays in objects, objects in arrays, objects in objects)

Answer 1

// first, we need the SQL results in the $result_array variable
$sql = 'SELECT ...';  // your SQL command
$result_array = $this->db->query($sql)->result_array();  // codeigniter code

// here the real answer begins
$result = array();

foreach ($result_array as $row)
{
    if (!isset($result[$row['authorid']])
    {
        $author = new StdClass();
        $author->authorid = $row['authorid'];
        $author->authorname = $row['authorname'];
        $author->books = array($row['books']);
        $author->favorited = array($row['favorited']);
        $result[$row['authorid']] = $author;
    }
    else
    {
        if (!in_array($row['books'], $result[$row['authorid']]->books))
        {
            $result[$row['authorid']]->books[] = $row['books'];
        }
        if (!in_array($row['favorited'], $result[$row['authorid']]->favorited))
        {
            $result[$row['authorid']]->favorited[] = $row['favorited'];
        }
    }
}

$result = array_values($result);
echo json_encode($result);