The `loadMissing` method in Laravel Eloquent is used to lazily eager load relationships only if they have not already been loaded on a model or collection of models. This prevents redundant database queries by checking if the relationship is already present before loading it.
How to use `loadMissing` with a specific subset of relationships
You can pass the specific relationships you want to load as arguments to the `loadMissing` method. This can be a single relationship or an array of relationships, including nested relationships using dot notation.
Example usage:
php
// Load only the 'author' relationship if not already loaded
$book->loadMissing('author');
// Load multiple relationships if missing
$book->loadMissing(['author', 'publisher']);
// Load nested relationships if missing
$book->loadMissing(['author', 'publisher.address']);
Important details
- `loadMissing` will only issue queries for relationships that are not already loaded on the model or collection. If a relationship is already eager loaded via `with()` or `load()`, it will skip loading it again.
- This is useful to avoid the N+1 query problem by ensuring you do not repeatedly query the same relationships.
- Unlike just accessing the relationship property (which triggers lazy loading), `loadMissing` explicitly loads the relationship beforehand, allowing you to customize the query with closures if needed.
- You can use `loadMissing` on both single Eloquent models and collections of models.
- It supports nested relationships using dot notation, so you can specify a subset of relationships precisely.
Why use `loadMissing` instead of just lazy loading?
Lazy loading happens automatically when you access a relationship property, but it triggers a query immediately at that point, which can cause multiple queries in loops (N+1 problem). Using `loadMissing` allows you to load missing relationships explicitly in advance, reducing the number of queries and improving performance.
Summary
To use `loadMissing` with a specific subset of relationships, simply call it on your model or collection and pass the relationships you want to ensure are loaded as arguments. It will load only those that are not already loaded, avoiding redundant queries and helping optimize your database interactions.
This method is especially useful when you want to conditionally load relationships that may or may not have been eager loaded earlier in your code, providing fine-grained control over relationship loading behavior[6].
Citations:
[1] https://www.bigthinkcode.com/insights/efficiently-executing-the-relationships-in-graphql
[2] https://piembsystech.com/data-relationships-between-types-in-graphql/?share=nextdoor&nb=1
[3] https://stackoverflow.com/questions/56622494/query-by-relationship-for-graphql
[4] https://github.com/nuwave/lighthouse/issues/1409
[5] https://lighthouse-php.com/6/api-reference/directives.html
[6] https://stackoverflow.com/questions/47238937/laravel-what-is-the-purpose-of-the-loadmissing-function
[7] https://slicknode.com/docs/data-modeling/relations/
[8] https://github.com/laravel/framework/discussions/43418