Can you show a code snippet using whenLoaded() to optimize queries

What is `whenLoaded()`?

`whenLoaded()` is a method that allows you to check if a relationship is already loaded on a model instance and then perform some action only if it is. This is useful for optimizing queries and avoiding the N+1 query problem by ensuring you don’t trigger additional lazy loading queries unintentionally.

How Does `whenLoaded()` Optimize Queries?

- Prevents unnecessary queries: It only executes code if the relationship data is already loaded.
- Avoids lazy loading: Prevents triggering additional queries when you access a relationship that isn’t loaded.
- Improves performance: By controlling when related data is accessed or transformed, it keeps the number of queries minimal.

Example Scenario

Suppose you have two models: `Post` and `Comments`. A `Post` has many `Comments`. You want to display the post along with the number of comments, but only if the comments are already loaded (e.g., eager loaded earlier).

Code Snippet Using `whenLoaded()`

php
// Assume $post is an instance of the Post model

// Eager load comments to avoid N+1 queries
$post = Post::with('comments')->find(1);

// Use whenLoaded to safely access comments count only if loaded
$commentsCount = $post->whenLoaded('comments', function ($post) {
    return $post->comments->count();
}, 0); // default to 0 if comments not loaded

echo "Number of comments: " . $commentsCount;

Explanation

1. Eager load `comments`: Using `with('comments')` ensures comments are loaded in one query.
2. Use `whenLoaded('comments', ...)`: This checks if the `comments` relationship is loaded.
3. Callback function: If loaded, it counts the comments.
4. Default value: If not loaded, it returns `0` to avoid triggering a lazy load.

Additional Example: Conditional Transformation

You can also use `whenLoaded()` to conditionally transform or append data only if the relationship is loaded.

php
$post = Post::with('comments')->find(1);

$commentsSummary = $post->whenLoaded('comments', function ($post) {
    return $post->comments->map(function ($comment) {
        return strtoupper($comment->content);
    });
}, collect()); // return empty collection if not loaded

foreach ($commentsSummary as $commentContent) {
    echo $commentContent . PHP_EOL;
}

Summary

- Use `whenLoaded()` to safely work with relationships only if they are preloaded.
- It helps avoid extra queries and improves performance.
- It’s especially useful in APIs or views where you want to conditionally include related data.

If you want, I can provide examples for other ORMs or frameworks too!