slake-school-service/app/Models/Paper.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;
use Illuminate\Database\Eloquent\SoftDeletes;

class Paper extends Model
{
    use SoftDeletes;

    protected $fillable = [
        'title',
        'authors',
        'university_id',
        'school_name',
        'published_at',
        'url',
        'summary',
        'source',
        'crawl_job_id',
        'external_id',
        'source_site',
    ];

    protected $casts = [
        'university_id' => 'integer',
        'crawl_job_id' => 'integer',
        'published_at' => 'date',
    ];

    public function university(): BelongsTo
    {
        return $this->belongsTo(University::class);
    }

    public function crawlJob(): BelongsTo
    {
        return $this->belongsTo(CrawlJob::class);
    }

    public function teachers(): BelongsToMany
    {
        return $this->belongsToMany(Teacher::class, 'teacher_papers')->withTimestamps();
    }
}