The `loadMissing` method in the context of GraphQL and ORM (such as Laravel's Eloquent) is used to load relationships that have not yet been loaded on a model instance. When dealing with nested relationships, `loadMissing` attempts to load the specified nested relations if they are not already loaded.
Handling of Nested Relationships by `loadMissing`:
- If you call `loadMissing` on a nested relationship, such as loading a nested relation of an already loaded parent relation, it may cause the parent relation to be reloaded. For example, if you have loaded a relation "inscriptions" and then call `loadMissing` on a nested relation within "inscriptions," Laravel will reload the "inscriptions" relation itself before loading the nested relation. This behavior means that `loadMissing` does not simply append missing nested relations but reloads the entire parent relation to ensure consistency[1].
- This reloading behavior is important to understand because it can affect performance by triggering additional database queries if nested relations are loaded incrementally rather than all at once.
- In practical terms, if you want to load multiple levels of nested relationships efficiently, it is generally recommended to eager load them upfront using methods like `with` rather than relying on `loadMissing` to fill in nested relations later. This approach avoids the overhead of reloading parent relations multiple times[8].
- For example, in Laravel Eloquent, eager loading nested relationships is done with syntax like:
php
$books = App\Book::with('author.contacts')->get();
This loads the `author` relationship and the nested `contacts` relationship in a single query or optimized queries. Using `loadMissing` for nested relations would reload the parent relation if not careful[8].
In the broader GraphQL context:
- Nested relationships in GraphQL are typically resolved by nested resolvers that fetch related data as needed. Efficient handling of nested data often involves batch loading or data loader patterns to avoid the N+1 query problem[3][10].
- When using ORMs or data layers under GraphQL, `loadMissing`-like functionality can be used to conditionally load related data if it hasn't been fetched yet, but care must be taken with nested relations to avoid redundant queries.
- Some ORMs or GraphQL frameworks provide specialized loaders or traits to load nested relations in batches, which can be stacked to load multiple nested levels, but often with limitations on how many levels can be eagerly loaded simultaneously[5].
Summary:
- `loadMissing` loads relations that are not already loaded on a model.
- When used on nested relations, it may reload the parent relation to ensure the nested data is consistent.
- This can lead to additional queries and potential performance issues if not managed carefully.
- For nested relationships, eager loading all necessary relations upfront is often more efficient.
- In GraphQL, nested resolvers and batch loading techniques are preferred to handle nested relationships efficiently.
This behavior is particularly noted in Laravel Eloquent's implementation of `loadMissing` where nested relations cause reloading of parent relations[1][8].
Citations:
[1] https://github.com/laravel/framework/issues/23027
[2] https://stackoverflow.com/questions/62563063/filtering-a-nested-relation-in-graphql
[3] https://compositecode.blog/2023/07/25/graphql-nested-queries-relationships-practices/
[4] https://github.com/fifemon/graphql-datasource/issues/15
[5] https://www.sea-ql.org/sea-orm-cookbook/001-how-to-load-nested-relation.html
[6] https://the-guild.dev/graphql/modules/docs/essentials/resolvers
[7] https://hasura.io/learn/graphql/hasura/relationships/
[8] https://stackoverflow.com/questions/35490728/laravel-eloquent-eager-loading-of-multiple-nested-relationships/53205641
[9] https://graphql.org/learn/execution/
[10] https://codesignal.com/learn/courses/advanced-graphql-data-patterns-and-fetching/lessons/nested-resolvers-and-data-relationships
[11] https://www.prisma.io/docs/orm/prisma-client/queries/relation-queries
[12] https://blog.gogrow.dev/nested-graphql-queries-in-python-using-strawberry-4c07e9962faa