[10.x] Add whenAggregated method to ConditionallyLoadsAttributes trait

[akr4m]

This PR introduces a new method, whenAveraged(), to the ConditionallyLoadsAttributes trait. This function is designed to work similarly to whenCounted(), but retrieves a relationship's column average value if it exists, expanding upon the trait's conditional loading capabilities.

Eloquent example with withAvg

$endpoints = $currentSite
            ->endpoints()
            ->withAvg('checks', 'response_time')
            ->get();

Eloquent Resource example with additional conditional relationship (whenAveraged)

public function toArray($request)
{
    return [
       'response_time_avg' => $this->whenAveraged('checks', 'response_time'),
    ];
}

The whenAveraged() method takes in a relationship, a column name, an optional value, and an optional default value. It generates an attribute name by appending the string 'avg' to the snake-cased version of the relationship name, followed by the column name. If this attribute does not exist in the resource's attributes, it returns the default value (or null if no default is provided).

This new method is particularly useful when dealing with large datasets where you want to conditionally load averages. It provides a convenient and readable way to handle such scenarios directly in the resource class, expanding upon the conditional loading capabilities of whenCounted().

[akr4m]

The eloquent also provides withMin, withMax, withSum, and withExists methods alongside withCount. And these methods place a {relation}_{function}_{column} attribute result.

So, in Eloquent Resources, some additional Conditional Relationships are sometimes necessary.

[taylorotwell]

Maybe this should depend on a more generic whereAggregated method to prevent future PRs for basically the same thing but for sum, min, max, etc.?

Please mark as ready for review if you want me to take another look.

[akr4m]

I've made updates based on the feedback received. The initial whenAveraged method has been replaced with a more generic whenAggregated method. This new method can handle multiple aggregate functions including min, max, avg, sum, exists, and more.

The whenAggregated method takes an additional parameter, $aggregate, which specifies the type of aggregation to perform. The attribute is then generated by appending an underscore, the aggregate function, and another underscore to the snake-cased version of the relationship name, followed by the column name.

[taylorotwell]

Could use a test or two?

[akr4m]

Could use a test or two?

Absolutely, I've added two tests along with the resource implementation. Please take a look and let me know if any adjustments are needed.