如何使用 Laravel 8 中的关系打印各个帖子的所有评论

Question

I am trying to print all comments per post using the relationship,

Error: Property [comments] does not exist on the Eloquent builder instance.

Post Model

  class WorkTravel extends Model
{
    use HasFactory;

    protected $table = 'work_travel';

    protected $fillable = ['name', 'role', 'location','salary','application_deadline','position','description'];


    public function comments()
    {
        return $this->hasMany(CommentWorkTravel::class);
    }

}

Comment Model

class CommentWorkTravel extends Model
{
    use HasFactory;

    protected $table = 'comments_for_work_travel';

    protected $fillable = ['message'];

    public function workTravel()
    {
        return $this->belongsTo(WorkTravel::class);
    }

}

Controller

    public function index(){

    $work_travels=WorkTravel::select('id','name','role','application_deadline')
        ->comments()
        ->paginate(6);

    dd($work_travels);
//Error: Call to undefined method \Database\Eloquent\Builder::comments().

Answer 1

Just use the ->comments() insted of ->comments Since all relationships also serve as query builders, you may add further constraints to the relationship query by calling the comments method and continuing to chain conditions onto the query:
your code should be sth like it

public function index(){

$work_travels=WorkTravel::select('id','name','role','application_deadline')
    ->comments()
    ->paginate(6);

dd($work_travels);

Answer 2

The error

Property [comments] does not exist on the Eloquent builder instance.

indicates that you are trying to recieve a value from something that is not a model instance.

See your line

$work_travels=WorkTravel::select('id','name','role','application_deadline')
    ->comments
    ->paginate(6);

You are selecting a row of type "WorkTravel" and than calling for the property "comments" (without () at the end). But what you get there is the relation defined in the model, not the result of a query with that relation.

It works like this

Model->relationshipmethod()->where('something,'searchvalue')->get()

or

Model->relationshipmethod()->all()

if you want to use the rows for a paginated table laravel also offers the paginate method which will recieve a subset of the rows and attach information for getting the previous and next page to the collection returned.

Model->relationshipmethod()->paginate()

To test that you should modify your statement to use the real model and a relationship method defined in that model. Not the select method

$WorkTravelID = 1; // get that from somewhere
$WorkTravel = \App\Models\WorkTravel::find($WorkTravelID);
$work_travels = $WorkTravel->comments()->paginate(6);
dd($work_travels);