A common refrain you'll hear about GraphQL is that you can make one request and get only the data you want. A query will return just the fields that you request, nothing more and nothing less. For example in the allLifts query, we make a selection for a certain set of fields:
When you start working with GraphQL, you'll start to realize that GraphQL is going to change your design process. Instead of looking at your APIs as a collection of REST endpoints, you'll start looking at APIs as collections of types. Before breaking ground on your new API, you need to think about, talk about, and formally define the data types that your API will expose. This collection of types is called a schema.
When Facebook open-sourced GraphQL, it had a few different parts. It came with a spec. That specification document described all of the features of the GraphQL query language and the schema definition language. It also came with a reference implementation of a GraphQL server called graphql.js. This was an example of what a GraphQL server might look like so that other people could implement their own servers in a variety of languages.
One of the most powerful features of GraphQL is its schema definition language. When we write a schema, we define all of the types that are available on our API. If our GraphQL server provides us with an enforced list of type definitions, that means that GraphQL gives us an added benefit: mocking.
When GraphQL was first released, some touted it as a replacement to REST. "REST is dead!" early adopters cried, and then encouraged us all to throw a shovel in the trunk and drive our unsuspecting REST APIs out to the woods. This was great for getting clicks on blogs and starting conversations at conferences, but painting GraphQL as a REST killer is an oversimplification. In fact, wrapping an existing REST API is a very effective way of migrating from REST to GraphQL.
The "QL" in GraphQL stands for the query language, and a key, yet often overlooked feature of the language is GraphQL fragments. A GraphQL query document can contain definitions for operations and fragments. Fragments are selection sets that can be reused in multiple operations.
The next in our series of articles from the Second Edition of Learning React is about useReducer.
Last week, we took a closer look at the useEffect Hook, but we still have yet to touch on one of the function's most important features: the dependency array.
