Laravel 5.2 - Odd Results When using Left Join on Subquery - mysql

Question

I have the following query:
$products = Product::leftJoin(DB::Raw('(SELECT imageable_id, MIN(created_at) as min_created_at
FROM images WHERE imageable_type = "App\\\Product"
GROUP BY imageable_id) AS subquery'), function($join) {
$join->on('subquery.imageable_id', '=', 'products.id');
})
->leftJoin('images', function ($join) {
$join->on('images.imageable_id', '=', 'subquery.imageable_id')
->where('images.created_at', '=', 'subquery.min_created_at');})
->select('products.*', 'images.file_path')
->paginate(5);
When I die and dump the query log, the above gets translated as follows:
"query" => """
select `products`.*, `images`.`file_path` from `products`
left join (SELECT imageable_id, MIN(created_at) as min_created_at
FROM images WHERE imageable_type = "App\\Product"
GROUP BY imageable_id) AS subquery on `subquery`.`imageable_id` = `products`.`id`
left join `images` on `images`.`imageable_id` = `subquery`.`imageable_id` and `images`.`created_at` = ?
limit 5 offset 0
"""
"bindings" => array:1 [
0 => "subquery.min_created_at"
]
Which looks correct, though I'm unsure why a binding has been added for subquery.min_created_at
Now when I execute the above the query in laravel images.file_path is always null when clearly I know there are related images. When I test the above query by pasting it and running directly in MySQL command line I get the expected results i.e. for products which have images, file_path for image is not null. The only difference when I run in MySQL command line is that I'm not doing any binding for subquery.min_created_at - I simply replaced the ? with subquery.min_created_at
Any ideas why the query is behaving this way. If I remove the second left join it works correctly but then I can't select the first created image to load e.g doing the following give me the file_path:
$products = Product::leftJoin(DB::Raw('(SELECT imageable_id, file_path
FROM images WHERE imageable_type = "App\\\Product"
GROUP BY imageable_id) AS subquery'), function($join) {
$join->on('subquery.imageable_id', '=', 'products.id');
})
->select('products.*', 'subquery.file_path')
->paginate(5);
Ideally I want to get my original query working in - any help appreciated.

Answer 1

You are using ->where() for your second join condition:
->where('images.created_at', '=', 'subquery.min_created_at')
This generates
and `images`.`created_at` = ?
which the binding is for.
Instead you should use ->on();
$join->on('images.imageable_id', '=', 'subquery.imageable_id')
->on('images.created_at', '=', 'subquery.min_created_at');