The N+1 Query Problem

A common performance pitfall that comes with the nested nature of GraphQL queries is the so-called N+1 query problem.

Let’s imagine we want to fetch a list of posts, and for each post, we want to add on the name of the associated author:

{
  posts {
    title
    author {
      name
    }
  }
}

Following a naive execution strategy, Lighthouse would first query a list of posts, then loop over that list and resolve the individual fields. The associated author for each post would be lazily loaded, querying the database once per post.

Eager Loading Relationships

When dealing with Laravel relationships, eager loading (opens new window) is commonly used to alleviate the N+1 query problem.

You can leverage eager loading by informing Lighthouse of the relationships between your models, using directives such as @belongsTo and @hasMany.

type Post {
  title: String!
  author: User! @belongsTo
}

type User {
  name: String!
  posts: [Post!]! @hasMany
}

Under the hood, Lighthouse will batch the relationship queries together in a single database query.

If you require a relation to be loaded for some field, but do not wish to return the relationship itself, you can use the @with directive.

Data Loader

webonyx/graphql-php allows deferring the actual resolution of a field until it is actually needed, read more in their documentation (opens new window).

You can extend \Nuwave\Lighthouse\Execution\DataLoader\BatchLoader if you require custom batch loading.