如何从具有父子关系的模型中获取下一个和上一个记录

Question

I have a parent child relationship in my model where a Section can have many subsections. so in my model I have joined the table onto itself and using a parent column I can determine which section is a parent / child.

My question is how would I retrieve the next and previous records for the subsections?

My Section model:

    class Section extends Model
    {
        use BelongsToSortedManyTrait, SortableTrait;


        public $fillable = [
            'id',
            'name',
            'description',
            'parent',
            'position'
        ];


        public function subsections() {
            return $this->hasMany(self::class, 'parent')->sorted();
        }

       public function next(){
        // get next record
        return self::where('id', '>', $this->id)->orderBy('id','asc')->first();

       }

       public  function previous(){
        // get previous record
        return self::where('id', '<', $this->id)->orderBy('id','desc')->first();

    }

    }

Notice the previous and next methods, at the moment they will work for all sections but won't take into account the parent / child relationship.

Any way I can achieve this?

Answer 1

This has not been tested but try:

self::where('parent', $this->parent)
    ->where('id', '<', $this->id)
    ->orderBy('id','desc')
    ->first();

Adding the parent to the query will restrict the next value to those with the same parent ID. You can then use like this:

$subsection = Section::find(2);
$next = $subsection->next();
$prev = $subsection->previous();

Furthermore, it may be better to make next and previous parent query optional:

public function next($parent = false) {
    $query = self::query();

    if ($parent) {
        $query = $query->where('parent', $this->parent);
    }

    $query = $query->where('id', '<', $this->id)
    ->orderBy('id','desc')
    ->first();
}

This will allow you to check the next and previous section as well as subsections.

All the best.

Update (API solution - this has not been tested)

$section = Section::find($id); // Whatever the section id is;

$subsection = Section::where('parent', $section->id)->first();

return [
    'section'         => $section,
    'next_section'    => $section->next()->id,
    'prev_section'    => $section->prev()->id,
    'subsection'      => $subsection,
    'next_subsection' => $subsection->next(true)->id,
    'prev_subsection' => $subsection->prev(true)->id,
];

On the next section call, you can then pass the subsection id and run next/prev before returning the api:

$subsection = Section::find(1)->next() ;

Answer 2

Try this:

public function next(){
    $id = $this->parent ?: $this->id;
    return self::where('id', '>', $id)->orderBy('id','asc')->first();
}

public  function previous(){
    $id = $this->parent ?: $this->id;
    return self::where('id', '<', $id)->orderBy('id','desc')->first();
}