MFS201 : Table of Contents

Chapter 1

Lesson 5

Resolvers in GraphQL

Learn the importance of resolvers in data retrieval and how they play a crucial role in GraphQL's flexibility. Dive into resolver chaining, a powerful technique for optimizing the performance and organization of your API.

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In this lesson, we will delve into GraphQL resolvers, which play a pivotal role in any GraphQL server. You'll learn how resolvers work, their role in the GraphQL ecosystem, and how to implement them effectively to handle intricate data fetching and manipulation tasks.

What are GraphQL resolvers and why do we need them?

Resolvers are functions that resolve the data requested by a GraphQL query or mutation. They serve as a bridge between your schema and your data sources, such as databases, APIs, or other GraphQL services. Resolvers are responsible for fetching, processing, and returning the requested data for each field in a query or mutation. Note that while the GraphQL schema has its own SDL, the resolvers can typically be written in any language, albeit with structural restrictions on how to write them.

When a query (or a mutation) reaches a GraphQL server from a user, the server requires both the schema to validate the query against and the resolver to define how to retrieve (or modify) the requested data.

In it’s simplest form, a GraphQL server can consist of only a single query and a resolver. In this example, the API has only one query — hello — that returns a static string response “Hey there!”.

Implementing resolvers

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