GraphQL is a typed query language for APIs. It includes a specification for making requests as well as a runtime environment for handling incoming requests. It includes many robust features including, but not limited to:
- Extensible, statically typed schemas
- Client-side schema introspection
- First class error handling and partial results
- Built-in deprecation mechanism
- Real-time subscriptions
GraphQL has implementations in many languages, can be served over different protocols (typically HTTP), and also facilitates powerful tooling. See the introduction to GraphQL for a basic overview of the specification and its usage.
This kata is built and run with Java 17 and uses GraphQL Java as its GraphQL
implementation for the basic query
and mutation packages. GraphQL Java is a framework-agnostic runtime that provides an API for defining GraphQL servers
which can be integrated with other technologies such
as Spring Boot.
JS GraphQL is a very useful plugin for GraphQL that is available from the IntelliJ marketplace.
The graphql-kata module includes a configuration file for JS GraphQL named .graphqlconfig; JS GraphQL will
automatically pick up this configuration file. After installing JS GraphQL, the plugin will detect schema files
contained in the project, which allows IntelliJ to provide syntax highlighting and completions in *.graphql files.
See the JS GraphQL documentation for more information.
The GraphQL Kata is separated into a few modules. graphql-kata-exercises contains the kata exercises that need to be
solved. graphql-kata-solutions contains the same exercises, but they are already solved. This can be referenced when stuck, or used to double-check solutions. The graphql-spring-boot-example module is explained below.
The kata is divided into a query package and a mutation package, the main two types of GraphQL operations. The packages should be done in order: query first and mutation second. Some of the query solutions will be used in the mutation tests.
GraphQL queries are read-only operations sent by a client to retrieve data from a GraphQL server. Queries allow clients to request, aggregate, and filter server-side data and receive a JSON formatted response.
The package bnymellon.jpe.graphql.kata.query in the src/test directory contains a series of failing query related
unit tests designed to teach the basics of making GraphQL queries. The src/test/resources/queries directory contains
several *.graphql files which need to be modified in order to make the tests pass. The schema for the query tests can
be found in graphql-composers-domain/src/main/resources/schema.graphqls.
GraphQL mutations represent the "C" (create), "U" (update), and "D" (delete) operations of the standard CRUD model. Mutations allow clients to perform these operations against the server and receive customizable JSON formatted responses in the same way they would from a query operation. Once you are familiar with making queries you are well on your way to understanding mutations and many of the same concepts and features still apply.
In the src/test directory there is a bnymellon.jpe.graphql.kata.mutation package which contains failing unit tests
designed to teach the basics of performing GraphQL mutations. The src/test/resources/mutation directory contains
several *.graphql files which need to be modified in order to make the tests pass. The schema for the mutation tests
is the same as for the query tests and can be found in graphql-composers-domain/src/main/resources/schema.graphqls.
There is a sample application contained in the graphql-spring-boot-example module. The application is a Spring Boot server using Spring for GraphQL. It continues using the same composers domain as the kata. You can run the server and execute operations against it to continue learning about the query language or browse through the code and learn how to spin up your own server.
The example app also exposes some tooling options that can be explored:
- GraphiQL is a browser based client with hints, completions, formatting, and a schema browser built in. It can be found at http://localhost:8080/graphiql while the sample application is running.