Laravel - 按关系表排序

Question

I have 2 tables issues and magazines and they have a relationship set up like this:

Magazines model:

 public function issues()
 {
     return $this->hasMany('App\Issue');
 }

Issues model:

public function magazine()
{
    return $this->belongsTo('App\Magazine');
}

In the magazines table I have a column order where the order number of the magazine is. I need to display the latest issue of each magazine, ordered by the magazine order. Now I am displaying latest issue of each magazine ordered by the date of issues.

        $issues = Issue::orderBy('date', 'desc')->get()->groupBy('magazine_id');

        foreach ($issues->first() as $issue)
        {
            $images[] = $issue->image;
        }

And that works fine. But with the new query:

         $magazines = Magazine::with('issues')->orderBy('order')->get();


        foreach ($magazines as $magazine)
        {
            $issues = $magazine->issues()->first();
            $images[] = $magazine->issues()->first()->image;
        }

I get the error:

Trying to get property of non-object

Answer 1

Just check if issue is_null, if not, add the image to $images:

    foreach ($magazines as $magazine)
    {
        $issue = $magazine->issues()->first();
        if (!is_null($issue) {
            $images[] = $issue->image;
        }
    }