BookStack/app/PageRevision.php

<?php namespace BookStack;


class PageRevision extends Model
{
    protected $fillable = ['name', 'html', 'text', 'markdown', 'summary'];

    /**
     * Get the user that created the page revision
     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
     */
    public function createdBy()
    {
        return $this->belongsTo(User::class, 'created_by');
    }

    /**
     * Get the page this revision originates from.
     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
     */
    public function page()
    {
        return $this->belongsTo(Page::class);
    }

    /**
     * Get the url for this revision.
     * @return string
     */
    public function getUrl()
    {
        return $this->page->getUrl() . '/revisions/' . $this->id;
    }

    /**
     * Get previous revision
     * @return \BookStack\PageRevision
     */
    public function getPrevious()
    {
        if ($id = PageRevision::where('id', '<', $this->id)->max('id')) {
            return PageRevision::find($id);
        }
    }

    /**
     * Get next revision
     * @return \BookStack\PageRevision
     */
    public function getNext()
    {
        if ($id = PageRevision::where('id', '>', $this->id)->min('id')) {
            return PageRevision::find($id);
        }
    }
}