Introduction to Resolvers in GraphQL

A resolver is a function that resolves a value for a type in your GraphQL schema. It provides the data for a specific field in a query and is responsible for fetching, transforming, and returning that data.

Key Takeaway: Resolvers are the core components that connect your GraphQL schema to your data sources.

• Separation of Concerns: Resolvers help keep your data-fetching logic separate from your schema definitions.
• Flexibility: You can easily change the data sources or logic without altering the schema.
• Reusability: Resolvers can be reused across different types and queries.

Resolvers are triggered when a client requests data from a GraphQL API. Here’s a step-by-step breakdown:

graph TD;
    A[Client Request] --> B[GraphQL Server];
    B --> C[Schema];
    C --> D[Resolvers];
    D --> E[Data Source];
    E --> F[Response to Client];
            

When a request is made, the server checks the schema, invokes the appropriate resolver function, and fetches the data from the source.

1. Keep Resolvers Small: Each resolver should be focused on a single field.
2. Avoid Side Effects: Resolvers should be pure functions that do not modify external state.
3. Use Data Loaders: Implement data loaders to batch and cache requests to optimize performance.