$spaceList = Space::where('user_id', $user_id)->pluck('space_id')->toArray();

$query = Interest::whereIn('space_id', $spaceList);

$query = Interest::whereHas('spaces', function($query) use ($user_id) {

    $query->where('user_id', '=', $user_id);

});

namespace App;

​

use Illuminate\Database\Eloquent\Model;

​

class Interest extends Model

{

    public function spaces()

    {

        // space_id is the column name in your space database table

        // id the the foreign-key target, generally is the primary-key of space table

        return $this->hasMany('App\Space', 'space_id', 'id');

    }

}

$spaceList = Space::where('user_id', $user_id)->pluck('space_id')->toArray();

$query = Interest::whereIn('space_id', $spaceList);