Laravel多重枢纽关系

Question

I'm struggling with creating a relationship between two pivots that share single model.

The pivots in question are item_tag and playlist_tag. Below I have described the table and the relationships I have created already.

So i can currently get items for playlists, playlists for items, tags for items, tags for playlists.

What i'm struggling to do is :

• Get items that share the same tags as a given playlist
• Get playlists that share the same tags as a given item

I believe this may be done with a 'manyThrough' but honestly i'm lost.

---

Some more relationship detail

• Playlist can be comprised of many items
• Items can belong to many playlists
• So item_playlist pivot

---

Tags can be applied to both playlists and items

• An item can have many tags
• tags can be applied to many items
• so item_tag pivot

---

• A playlist can have many tags
• tags can be applied to many playlists
• so playlist_tag pivot

---

Example table structure

   Table : items
    id
    name

    Table : playlists
    id
    name

    Table : item_playlist
    item_id
    playlist_id

    Table : tags
    id
    name

    Table : item_tag
    item_id
    tag_id

    Table : playlist_tag
    playlist_id
    tag_id

---

Example class / relationship structure

class Playlist extends Model
{
    public function items()
    {
        return $this->belongsToMany(Item::class)->withTimestamps();
    }

    public function tags()
    {
        return $this->belongsToMany(Tag::class)->withTimestamps();
    }
}
...
class Item extends Model
{
    public function playlists()
    {
        return $this->belongsToMany(Playlist::class)->withTimestamps();
    }

    public function tags()
    {
        return $this->belongsToMany(Tag::class)->withTimestamps();
    }
}
...
class Tag extends Model
{
    public function items()
    {
        return $this->belongsToMany(Item::class)->withTimestamps();
    }

    public function playlists()
    {
        return $this->belongsToMany(Playlist::class)->withTimestamps();
    }
}

Answer 1

Getting the items that share at least one tag with a given playlist:

$tags = $playlist->tags()->pluck('id');
$items = Item::whereHas('tags', function($query) use($tags) {
    $query->whereIn('id', $tags);
})->get();

Getting the items that share all the tags with a given playlist:

$tags = $playlist->tags()->pluck('id');
$items = Item::whereHas('tags', function($query) use($tags) {
    $query->whereIn('id', $tags);
}, '=', $tags->count())->get();

The reverse direction works the same way.