tethys/app/Transaction.php

<?php
namespace App;

use Illuminate\Database\Eloquent\Model;

class Transaction extends Model
{

    protected $fillable = [
        'student_id',
        'book_id',
        'borrowed_at',
        'returned_at',
        'fines',
        'status'
    ];

    public function student()
    {
        return $this->belongsTo('App\Person', 'student_id');
    }

    public function book()
    {
        //model, foreign key in tsis model, primary key of relation
        return $this->belongsTo('App\Book', 'book_id', 'id');
    }

    public function scopeNotReturnedYet($query)
    {
        return $query->where('status', 0);
    }

    public function scopeReturned($query)
    {
        return $query->where('status', 1);
    }
}