**Course Title:** Building Mobile Applications with React Native **Section Title:** Working with APIs and Data Fetching **Topic:** Understanding REST APIs and GraphQL Welcome to this topic, where we will explore the world of APIs and data fetching in React Native. In this topic, we will focus on understanding REST APIs and GraphQL, two popular technologies used for building web APIs. **What are APIs?** Before we dive into REST APIs and GraphQL, let's define what an API is. An API, or Application Programming Interface, is a set of rules and protocols that allows different software systems to communicate with each other. In the context of web development, APIs enable data exchange between a client (e.g., a mobile app) and a server. **REST APIs** REST (Representational State of Resource) APIs are a type of web API that uses HTTP (Hypertext Transfer Protocol) requests to interact with a server. REST APIs are designed to be simple, flexible, and scalable. Here are the key concepts of REST APIs: * **Resources**: In REST, resources are the main entities that are being manipulated (e.g., users, products, orders). Each resource is identified by a unique identifier (e.g., user ID). * **HTTP Methods**: REST APIs use standard HTTP methods (GET, POST, PUT, DELETE) to perform CRUD (Create, Read, Update, Delete) operations on resources. + **GET**: Retrieve a resource or a collection of resources. + **POST**: Create a new resource. + **PUT**: Update an existing resource. + **DELETE**: Delete a resource. * **Endpoints**: Endpoints are URLs that define the location of a resource. For example, `/users` or `/orders/123`. * **Request Headers**: Request headers provide additional metadata about the request. For example, authentication tokens or content type. Here's an example of a REST API endpoint for retrieving a user's profile: `GET /users/123` Request: * `Header: Authorization: Bearer <token>` * `Body: none` Response: * `Content-Type: application/json` * `Body: {"id": 123, "name": "Jane Doe", "email": "jane.doe@example.com"}` **GraphQL** GraphQL is a query language for APIs that allows clients to define exactly what data they need. Unlike REST, GraphQL uses a single endpoint for all queries and mutations. Here are the key concepts of GraphQL: * **Schema**: GraphQL schema defines the structure of the data. It includes types, queries, mutations, and resolvers. * **Queries**: Queries are used to retrieve data. They can include fields, arguments, and directives. * **Mutations**: Mutations are used to update data. They can include fields, arguments, and directives. * **Resolvers**: Resolvers are functions that resolve queries and mutations. Here's an example of a GraphQL query for retrieving a user's profile: ```graphql query { user(id: 123) { id name email } } ``` Request: * `Method: POST` * `Body: {"query": "query { user(id: 123) { id name email } }"}` Response: * `Content-Type: application/json` * `Body: {"data": {"user": {"id": 123, "name": "Jane Doe", "email": "jane.doe@example.com"}}}` **Comparison between REST and GraphQL** | | REST | GraphQL | | --- | --- | --- | | **Request structure** | Multiple endpoints for each resource | Single endpoint for all queries and mutations | | **Request method** | GET, POST, PUT, DELETE | POST (for queries) | | **Data retrieval** | Retrieve all data or nothing | Retrieve only the requested data | | **Performance** | Can lead to under-fetching or over-fetching | Optimal data retrieval | | **Security** | Limit data exposure using request headers and authentication | Use resolvers to limit data exposure | **Conclusion** In this topic, we explored REST APIs and GraphQL, two popular technologies used for building web APIs. We learned about the key concepts, advantages, and disadvantages of each technology. In the next topic, we will cover fetching data using the `fetch` API and Axios in React Native. **Additional Resources** * [RESTful API Tutorial](https://www.restapitutorial.com/) * [GraphQL Tutorial](https://graphql.org/learn/) * [GraphQL vs REST](https://medium.com/@alexmngn/graphql-vs-rest-when-the-choice-is-clear-43c21efb6caf) **Exercise** * Create a simple REST API using Node.js and Express.js. * Create a simple GraphQL API using Apollo Server. **Leave a comment or ask for help** If you have any questions or need help with this topic, please leave a comment below.