laravel join table if data exists - join

Question

What is the best way to join table A with table B, if table B has data and if not just give me data from table A? because if I do it in this way, and there are no photos in table B I don't get data from that row from table A.
$data = Category::join('photos', 'categories.cover_id', '=', 'photos.id')
->get(['categories.id',
'categories.position',
'categories.visible',
'categories.created_at',
'categories.updated_at',
'categories.title',
'photos.filename']);
return $data;
my idea is just to make another request to get all data from table A where categories.cover_id is 0 (without join)
my tables are just
table A (categories)
-------------------------------
| id | title | cover_id | ... |
-------------------------------
| 1 | lorem | 1 | ... |
-------------------------------
| 2 | ipsum | 12 | ... |
-------------------------------
| 3 | dolor | 0 | ... |
-------------------------------
table B (Photos, there is no data for dolor, because i created dolor recently in table A)
---------------------------------
| id | title | filename | ... |
---------------------------------
| 1 | lorem | lorem.jpg | ... |
---------------------------------
| .. | ..... | ...jpg | ... |
---------------------------------
| 12 | ipsum | ipsum.jpg | ... |
---------------------------------

Answer 1

You should be fine by just using a leftJoin(). A normal ("inner join") will only return results from both tables. But a left join returns all results from the left table (in this case categories) and everything that exists from the other table.
$data = Category::leftJoin('photos', 'categories.cover_id', '=', 'photos.id')
->get(['categories.id',
'categories.position',
'categories.visible',
'categories.created_at',
'categories.updated_at',
'categories.title',
'photos.filename']);
Or you could...
Use the power of Eloquent
You only need to define the relationship (I assume you already have a Photo model) and this gets a lot easier
class Category extends Eloquent {
public function photos(){
return $this->hasMany('Photo', 'cover_id');
}
}
And then...
$data = Category::with('photos')->get();
And you will have the photos model nested inside the category models. Accessible like this:
foreach($data as $category){
foreach($category->photos as $photo){
echo $photo->filename;
}
}

Answer 2

I would rather do it this way:
// Just assuming a few variables for better understanding
$allCategories = Category::all();
foreach ($allCategories as $category) {
$photo = Photo::find($category->cover_id);
if ($photo) { // $photo!=null or isset($photo) - you can use anything
// photo is found do the additional processing
}
//proceed with your normal processing
}