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What is GraphQL APIs?

GraphQL is an open-source query language for APIs and a server-side runtime for executing those queries. It's essentially a protocol that dictates how a client (like a mobile app or website) can request data from a server, providing a more efficient and flexible alternative to traditional API designs like REST.

Core Theory and Concepts

GraphQL is built around a few key theoretical concepts:

1. Schema and Type System

A GraphQL Schema is the central component and acts as a contract between the client and the server. It uses a Strongly-Typed system to precisely define all the data that a client can request.

Types: The schema defines the structure of data in terms of Object Types, which are named collections of fields. For example, a User type might have name, email, and posts fields.

Fields: These are the units of data that can be requested on a type. Each field has a defined data type (like String, Int, or another custom Object Type). The presence of these types allows for validation of a query before execution and ensures predictable responses.

2. Client-Specified Requests

This is the most significant departure from traditional APIs. In GraphQL, the client declares exactly what data it needs in a single request.

Queries: These are used to fetch data. A client sends a query that mirrors the structure of the data it expects to receive. The server then returns a response that contains only the requested fields, which solves the problem of over-fetching (getting more data than you need) common in fixed-endpoint APIs.

Mutations: These are used to modify data (create, update, or delete). Like queries, they specify the data that should be changed and the desired data to be returned after the change is complete.

Subscriptions: These enable real-time data streams, allowing a client to subscribe to a specific event and receive updates from the server whenever that data changes.

3. Single Endpoint

Unlike a traditional REST API, which may expose many different endpoints (URLs) for different resources (e.g., /users, /posts/123), a GraphQL API typically exposes only a single endpoint. All data fetching and modification requests are sent to this one URL, with the specific operation (query or mutation) and the requested data shape defined in the request body.

4. Resolvers

While the schema defines what data can be fetched, Resolvers define how to actually retrieve that data for each field in the schema.

A resolver is a function associated with a specific field on a type.
When a client sends a query, the GraphQL server executes the relevant resolver functions for all the requested fields.
Resolvers act as the bridge between the GraphQL layer and the underlying data sources (like databases, microservices, or even other REST APIs). They hide the complexity of the back-end from the client, meaning the client only sees a unified "graph" of data.

Key Benefits

Efficiency: Clients only get the data they ask for, minimizing data transfer, which is especially beneficial for mobile applications and limited bandwidth.
Flexibility: The client controls the data requirements, allowing for rapid front-end changes without requiring the back-end to change fixed endpoints.
API Evolution: New fields can be added to the schema without affecting existing clients, allowing the API to evolve without needing disruptive versioning (like v1, v2).

To validate a GraphQL API using Rest Assured in Java, follow these key steps:

Public GraphQL API for Example

We'll use the public GraphQL API from https://countries.trevorblades.com/

Endpoint: https://countries.trevorblades.com/

Example Query (returns name and capital of India):

{
  country(code: "IN") {
    name
    capital
  }
}

Java Code Using Rest Assured

import io.restassured.RestAssured;
import io.restassured.response.Response;
import org.json.JSONObject;

import static io.restassured.RestAssured.given;
import static org.hamcrest.Matchers.equalTo;

public class GraphQLApiTest {

    public static void main(String[] args) {

        // GraphQL query as string
        String query = "{ country(code: \"IN\") { name capital } }";

        // Prepare the JSON body
        JSONObject requestBody = new JSONObject();
        requestBody.put("query", query);

        // Set base URI
        RestAssured.baseURI = "https://countries.trevorblades.com/";

        // Send POST request and validate response
        given()
            .header("Content-Type", "application/json")
            .body(requestBody.toString())
        .when()
            .post()
        .then()
            .statusCode(200)
            .body("data.country.name", equalTo("India"))
            .body("data.country.capital", equalTo("New Delhi"));
    }
}

Code explanation:

(a) Define Graph ql query in string form

(b) Define json body by using JSONObject class

(d) Set POST request

(e) Get response and validate response.

Validations Performed

HTTP status code = 200
Country name = "India"
Capital = "New Delhi"

Maven Dependencies:

<dependency>
    <groupId>io.rest-assured</groupId>
    <artifactId>rest-assured</artifactId>
    <version>5.3.0</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20210307</version>
</dependency>

How to test Graph QL API in Rest Assured

Validations Performed