Changing own id in pivot table - php

Question

I'm developing a Laravel application where I have a posts table, a tags table and a post_tag table which acts as a pivot table.
Now I need to give all the tags from a post to another post. In other words I need to make:
$tags = $post->tags;
And change the post_id to each record in the pivot table. I have all the relationships already set.
EDIT: this is my code
class Post extends Model
{
public function tags()
{
return $this->belongsToMany(Tag::class)->withPivot('is_active')->withTimestamps();
}
}
class Tag extends Model { }
The main problem is that I have to keep the is_active value as it is. I just need to replace the post_id from the pivot table where post_id equals the one I want to override (I know I could make a raw query but I'm trying to avoid it)
EDIT 2:
I made it work this way but I still prefer an object oriented way
DB::table('post_tag')->where('post_id', $post_a->id)->update(['post_id' => $post_b->id]);

Answer 1

You can use the method updateExistingPivot of Eloquent, from the laravel documentation:
If you need to update an existing row in your pivot table, you may use updateExistingPivot method. This method accepts the pivot record foreign key and an array of attributes to update:
$user = App\User::find(1);
$user->roles()->updateExistingPivot($roleId, $attributes);

Answer 2

Try something like
$tags = $post->tags;
//convert tags to IDs only for upcoming steps
... //an array of IDs
$post->tags()->sync($tags); //remove the tags from this post
$post2->tags()->sync($tags); // add the tags to this post
This should get you to the right tracks.
Update
If it was only one, this would do
$post2->tags()->attach($tag, ['is_active' => true]);
$post2->tags()->->sync([1 => ['is_active' => true], 2 => ['is_active' => true]);
You can try to adapt the example above.
But I have no idea how to do it with an array of IDs.