Laravel-translatable - "call to a member function save() on string" - php

Question

(Updated) I use the laravel-translatable package and trying to insert rows with translations. When trying to save, it gives me the error "call to a member function save() on string".
I loop an object with keys and values, like: "food": "Nourriture",
and inside the loop I do a select of the Translations table:
$translationKey = \App\Translation::select('group', 'key')->where('group',
'global')->where('key', $key)->first();
I don't do exactly as the documentaion, which would have been:
$translationKey = \App\Translation::where('key', $key)->first();
The difference is that I select the columns 'group' and 'key', and I do an extra "where" to specify that group = global. Isthere anything wrong there?
Then I try to check if there is an already existing translation. If not, I insert the translation:
if($translationKey->hasTranslation('fr')) {
continue;
}else{
//insert
$translationRow = $translationKey->translateOrNew('fr')->$key = $value;
$translationRow->save();
}
I use translateOrNew instead of translate , because otherwise I get error: "Creating default object from empty value".
It seems I can't do the ->save() method because it's a string, not a model instance which it should be. So I guess there is something wrong with this line?:
$translationKey = \App\Translation::select('group', 'key')->where('group',
'global')->where('key', $key)->first();
But what is the problem?

Answer 1

I had some mistakes - I needed to select the whole row instead of individual columns:
$translationKey = \App\Translation::where('group', 'global')
->where('key', 'about_us')
->first();
And there were mistakes when saving the translation. My translations_translations table has a "value" column, so this worked:
$translationKey->translateOrNew($locale)->value = $value;
$translationKey->save()