What Is GraphQL

GraphQL transforms web development by streamlining data interactions and optimizing workflows. It enables developers to build more efficient, flexible APIs that adapt seamlessly to evolving application needs.

What Is GraphQL?

GraphQL is a query language and server-side runtime technology for application programming interfaces (APIs) that lets you fetch exactly the data you need from a single endpoint using structured queries.

It describes how clients communicate with the server and request only the needed data. It supports reading, updating, and real-time data delivery in a client-defined format.

As a developer, you can create requests to fetch data from multiple sources with a single API call. It also allows you to build APIs using your preferred architectural approach while remaining predictable to clients. For example, in marketplace apps, GraphQL simplifies pulling order and user data in one go.

How Does GraphQL Work?

To fully understand how this query language works, it's essential to look into each of the main components:

• Schemas. The schema serves as the blueprint for a GraphQL API. It defines the data fields and their types, as well as the relationship between types. Types are custom objects that define what can be queried from the API. The schema defines how the client can request data, specifying the capabilities of the API.
• Queries. A query is the structure you use to get data. Queries fetch data by allowing clients to specify exactly which fields are needed, making sure that the server returns only the requested information.
• Mutations. Mutations are operations that devs can use to change (create, update, or delete) data on the server. They function similarly to queries but handle data modifications.
• Resolvers. A resolver is a function that determines how data is fetched and returned after a query is received. It acts as a bridge between the client's request and the data source and populates the data for all requested fields.
• Subscriptions. Subscriptions are read operations that deliver real-time updates whenever a server-side event occurs during runtime. Subscriptions use WebSocket connections to maintain active connections to the server.
• Execution engine. The execution engine is at the core of all GraphQL operations. It takes a validated query and determines the resolvers to be invoked. After execution, it compiles the response into a payload that reflects the original query.

The process of handling queries involves several steps. When the server receives the request, it validates it against a pre-defined schema to make sure the requested fields and types exist. It also determines the resolver functions to call.

The schema defines the data structure on the server and how they relate. The query is parsed and executed by calling the appropriate resolver, which helps retrieve data from various sources such as databases, third-party APIs, or static files.

Once the resolver completes retrieving data, the execution engine creates a response payload containing the requested data. This response returns only the requested data without any extra fetching.

Key Features of GraphQL

GraphQL provides a powerful set of features that make API development seamless. These include:

• A strong typing system that defines data types and query structures, including available operations and the relationships between fields. This schema provides clear guidelines, guaranteeing that the query is executed as it is.
• Declarative data fetching does not rely on endpoints. Clients use single, structured queries to avoid over-fetching (retrieving more data than needed) or under-fetching (getting insufficient data). 
• Datasets allow developers to combine multiple data sources into one comprehensive API. Unlike in REST, where you must make multiple API endpoints to get different data, it allows you to encapsulate fetching data in a single request. This saves time and reduces the amount of data sent over the network. Combining multiple queries into one also means less client-side code while making it easy to build complex UI components.
• Filtering allows you to select data based on specific criteria of your choice. These filters are essential for improving accuracy, especially when dealing with large volumes of data.
• A hierarchical structure mirrors the underlying data. This structure allows nested queries, making it possible to retrieve multiple data fields in a single request.
• Sorting means organizing or ordering data in a specific way, such as chronologically, ascending, or descending. This feature applies to data that follows a specific sequence and helps retrieve it in a structured way. Sorting enables faster processing and understanding of the relationship between data points.
• Pagination breaks down data retrieval into small, manageable chunks, reducing server load and improving app performance, especially for those with long lists.
• A single endpoint simplifies the API structure by eliminating the need to maintain multiple routes and improves security and authentication.

All the above features make GraphQL a great alternative to REST APIs and simplify operations that would otherwise be difficult to handle.

GraphQL vs. REST

Both GraphQL and REST help build web applications. REST is an architectural style that uses a stateless, client-server protocol for data exchange and is a great alternative to this query language in certain situations.

While these two query languages facilitate efficient data exchange, they function in different ways. Below are some of the key differences between the two API architectures:

Architecture

GraphQL uses a single endpoint and a defined schema as a contract between the client and the server. It makes sure that the response matches the request and is of the expected type.

In contrast, REST uses multiple endpoints for different resources, using standard HTTP methods (GET, POST, PUT, and DELETE) to perform operations on the endpoints without enforcing a server-side schema. The GET method requests data retrieval, while the POST method creates new resources. The PUT method updates resources, while the DELETE method deletes resources.

Data Fetching

GraphQL allows clients to specify the fields to retrieve with the server responding with a JSON payload. On the other hand, REST APIs return complete resources depending on the endpoint you use. The client receives every piece of data associated with the resource.

Operations

GraphQL supports three main operations: query, mutation, and subscriptions. Queries are for retrieving data, mutations for creating, updating, or deleting data, and subscriptions for real-time updates. In contrast, REST APIs use the HTTP methods mentioned above to manage data interactions.

Use Cases

GraphQL is useful in apps with complex, dynamic, or interrelated data requirements. It returns the data that the client needs, reducing memory usage and improving performance. REST is ideal for resource-driven and simpler apps where the data model doesn't change frequently.

Versioning

GraphQL does not need versioning, as outdated fields are deprecated without breaking existing queries. Adding new fields to the server does not affect clients who do not need those fields.

Significant changes to REST APIs require versioning. Developers include version numbers in the URL (for example, /API/v1/users or /API/v4/locations) to maintain backward compatibility and prevent service disruptions.

Error Handling

GraphQL returns errors as part of the response body under the 200 status code for all responses. Clients must parse through the payload to establish whether the request was successful. Whenever there is an error in the query execution, it returns individual errors in the response body for fields or operations on that query.

REST uses HTTP status codes to indicate the status of a request. These status codes have a specific meaning. For example, 200 means the request was successful, 404 means the requested resource is unavailable, and 500 indicates a server error.

GraphQL and REST are two different architectural styles for designing APIs. GraphQL operates through a single endpoint, allowing the client to send a query to the server that specifies exactly what data is needed. In contrast, REST uses multiple endpoints, often requiring the client to combine resources from several of them to fetch data. When it comes to operations, GraphQL uses queries, mutations, and subscriptions, whereas REST relies on standard HTTP methods like GET, POST, PUT, and DELETE. GraphQL is typically used in complex applications with interconnected data sources, while REST is more common in simpler apps. For versioning, GraphQL tends to deprecate unneeded fields instead of introducing new versions, whereas REST often uses versioning to manage major changes and ensure backward compatibility. In terms of error handling, GraphQL includes errors directly in the response body, while REST primarily communicates errors through HTTP status codes.

When To Use GraphQL

Some of the best use cases include:

GraphQL is ideal for mobile applications where performance is crucial. It allows clients to extract the needed data, benefiting devices with limited resources like smartphones and smartwatches.

GraphQL acts as a powerful aggregation layer in a microservices architecture. Having only one endpoint enables you to retrieve data in a single request, simplifying client-side logic and easing complex backend maintenance.

Developers use this query language for rapid application prototyping because of its flexibility and self-documenting nature. It automatically exposes its structure through built-in introspection queries. Developers can easily explore the available queries, types, and fields without requiring additional documentation. This makes understanding and working with the API simpler as it evolves.

Headless Content Management Systems (CMSes) use the query language to serve tailored content to frontend clients. You can use a headless CMS platform like Hashnode or Contentful to create your content (for example, blogs) and fetch that into your web app using GraphQL API calls. This approach simplifies content management and allows for dynamic content across multiple platforms.

GraphQL's subscription mechanism allows real-time updates, making it useful in applications that require feeds, such as analytics platforms and live dashboards.

Social media platforms use it to provide dynamic content and enhance real-time user interactions. It can fetch multiple data relations in a single query, such as user profiles, likes, shares, comments, and posts.

Frequently Asked Questions