检索子关系时，Laravel 5.5关系不起作用

Question

I have a Laravel 5.5 app that has an edit or update function that has two dropdowns. One dropdown is the parent and the second dropdown is it child relationship. So basically the first dropdown has many second dropdown thats the case.

Now about the code in my controller

$services = Service::all()->sortBy('code', SORT_NATURAL | SORT_FLAG_CASE)->pluck('description', 'id');
$categories = Service::with('categories')->get()->sortBy('categories.name', SORT_NATURAL | SORT_FLAG_CASE)->pluck('categories.name', 'categories.id');

I used a pluck method that will retrieve only the name and the id of the categories which is the child relation of service like what I have said. A service has many categories and I only want to display the categories in the dropdown based on the selected service in the dropdown which is automatically chosen base on existing record with the help of Laravel pluck.

However the second dropdown or the categories is empty or the second query is not working.

Here is how I defined my relationship in the service model.

public function categories()
{
   return $this->hasMany('App\Models\Categories', 'service_id', 'id');
}

Now the code in my blade file

<div class="form-group col-sm-6">
    {!! Form::label('service_id', 'Service:') !!}
    {!! Form::select('service_id', $services, null, ['class' => 'form-control input-md','required', 'id' => 'service_id'])!!}
</div>

<div class="form-group col-sm-6">
    {!! Form::label('categories_id', 'Category:') !!}
    {!! Form::select('categories_id', $categories, null, ['class' => 'form-control input-md','required', 'id' => 'category_id'])!!}
</div>

Appreciate if someone could help. Thanks in advance.

Answer 1

I would take a look at the values you are passing to pluck. Since you are generating a new collection with the second query, I believe you should be able to call pluck('name', 'id');. The categories.column_name is used to avoid ambiguity in the query, but all the collection is doing is retrieving models, so if you use the property names without the table prefix - you should get what you're after.

I previously assumed that you were handling the sorting via query; since you are handling that at the collection level as well, I'd remove the categories prefix from that field too. You could also adjust the query to use the ->orderBy() method and pass the field names as an array to get (like so: ->get(['name', 'id'])). It all depends on your needs - if my first suggestion doesn't work for you, you could move the sorting and filtering to the query. Hope that helps some.