# 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 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.

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