GraphQL is a query language and runtime that was developed by Facebook. It is an alternative to REST (Representational State Transfer), which is the traditional approach for building APIs (Application Programming Interfaces) for web and mobile applications. The main advantage of GraphQL over REST is that it allows clients to request only the data they need, making network requests more efficient and reducing overfetching and underfetching. GraphQL also provides a strongly-typed schema that defines the data model and operations that are available to clients, making it easier to reason about and evolve APIs.
GraphQL is used for building APIs that serve data to client applications. With GraphQL, clients can request exactly the data they need, in a single request, without overfetching or underfetching. This is achieved through the use of a flexible and expressive query language that allows clients to specify the exact fields they need, including nested and related fields. The server then responds with a JSON object that matches the shape of the requested query.
GraphQL also allows clients to perform mutations, which are operations that modify data on the server. Mutations are similar to queries, but they use the HTTP POST method instead of GET. Mutations are typically used for creating, updating, or deleting data, and they allow clients to specify the exact fields that should be modified.
In addition to queries and mutations, GraphQL also supports subscriptions, which allow clients to receive real-time updates when data changes on the server. Subscriptions are implemented using WebSockets, and they allow clients to subscribe to a specific event or set of events on the server. This makes it easy to build real-time applications such as chat, notifications, and live dashboards.
Overall, GraphQL is a powerful and flexible tool for building APIs that serve data to client applications. Its ability to provide clients with only the data they need, in a single request, makes it an attractive alternative to REST. With its strongly-typed schema and support for mutations and subscriptions, GraphQL is a great choice for building modern, real-time applications.