What is GraphQL Schema and How Does it Work?

Explore GraphQL Schema Types and Give Your Clients a Complete Picture of Accessible Data
Anthony Molzahn

Creating APIs has always been a tedious process, which is why GraphQL schemas are so useful to developers today. 

Using GraphQL schema allows us to describe the functionality available to the client applications that connect to it.  With GraphQL schema, developers can show their clients exactly what data is available and request a specific subset of that data with a single optimized query. GraphQL schema also aims to prevent both over-fetching and under-fetching issues by allowing the client to request only the relevant data.

Is your curiosity piqued? If you’re ready to learn all of the ins and outs about GraphQL schemas, then this is the post for you. We’re going to cover why you should use GraphQL schema to describe the shape of your available data, detail how GraphQL schema works, and explore the key benefits of GraphQL schema. Plus, we’ll show you how Devii can take GraphQL even further.

Let’s dive in!

What is GraphQL?

First up, before we launch into our detailed explanation of GraphQL schemas, let’s answer the question: what is GraphQL? Released in 2015, GraphQL is a query language and server-side runtime for APIs (application programming interfaces) that prioritizes giving the user the exact, specific data requested.

As an alternative to REST, GraphQL allows developers to perform requests that pull data from multiple data sources into a single API call. In short? GraphQL makes APIs faster, more flexible, and developer-friendly. 

GraphQL involves multiple elements within the query language, including (you guessed it!) GraphQL schemas.

What is a GraphQL schema?

A GraphQL schema describes the shape of the data your API makes available. Schemas are made up of object types, which define which kind of object you can request and what fields it has. A GraphQL schema also specifies which queries and mutations are available to execute. 

Queries and mutations are the most common GraphQL operations.

👓 Queries read the available data.

Mutations involve the creation, updating, or deleting of the data.

Be sure to remember: the schema is not responsible for defining where data comes from or is stored. A GraphQL schema only shows what the available data looks like.

How does GraphQL schema work?

GraphQL schema enables developers to see what data is available and to request a specific subset of that data with a query. But, let’s break it down even more.

Here’s exactly how GraphQL schema works, in 4 simple steps:

  1. First, API developers use GraphQL to create a schema that describes all possible data available to query through that service.  
  2. Next, once the queries roll in, GraphQL validates the queries against the schema. 
  3. Third, GraphQL executes the validated queries.
  4. Last, the API developer attaches each field in a schema to a resolver, which specifies how each request will return data to the client.

GraphQL Schema Use Case

To demonstrate how GraphQL schema works, let’s run through a use case. Let's say you’re creating an app highlighting restaurant specials (i.e. brunch, happy hour, prix fixe) in your town. The app needs to show the restaurant name (“Tastee Restaurant”), type of special (“brunch”), frequency of the special (“Sunday 8 am - 2 pm”), and perhaps the star rating. 

Change this graphic to reflect the restaurant specials

type Book {

  title: String

  author: Author


type Author {

  name: String

  books: [Book]



All of these types can be populated with data from different data sources, including a restaurant’s website, a back-end database, or a review website like Yelp. 

Now that we’ve gone over how a GraphQL schema works, let’s talk GraphQL Schema types.

GraphQL Schema types

Every type of GraphQL schema falls into one of the following categories:

  • Scalar - similar to primitive types in programming languages, scalars resolve to concrete data. The most common scalars are:
  • Int: signed 32‐bit integer
  • Float: signed double-precision floating-point value
  • String: UTF‐8 character sequence
  • Boolean: true or false
  • ID: often used to refetch an object or as the key for a cache. Serialized as “String.” 
  • Object - represents which object you can fetch, and what fields it has. Most of the types in a GraphQL schema are object types.
  • Input - an object type that groups a set of arguments together, especially when it comes to mutations. This set can be used as an argument to another field. 
  • Enum - represents a predefined list of possible values and helps ensure data values are consistent.
  • Union - an abstract GraphQL type. Unions allow schema fields to return one of multiple object types.
  • Interface - defines a set of fields that must be included by an object in order to implement that specific interface.

After being able to recognize the various schema types, let's examine the main advantages of schemas and see why they matter. What can GraphQL schemas really do for you?

What are the major benefits of a GraphQL schema?

To start, one of the biggest benefits of a GraphQL schema is that it serves as the ultimate source of truth in a GraphQL application and opens up a pathway for an enterprise to federate its entire API. 

With GraphQL, development is faster than it is with REST. This is also thanks to the GraphQL schema, which serves as the single endpoint that handles everything. Instead of having to write a new endpoint every time, the database structure changes, like adding a new column.

Additionally, another significant benefit of a GraphQL schema is that it gives the client more freedom in the fetched data. With GraphQL calls, everything is handled in a single query, and clients can receive their request without the risk of overfetching.

FInally, it’s important to note that a GraphQL schema also allows an application API to evolve without busting existing queries, and can work with existing API management tools.

If a GraphQL schema sounds like an enticing option to streamlining your API management, then it’s time to meet Devii.

How Devii Uses GraphQL Schemas to Deliver Data Faster

We made Devii because we wanted to make API development easy, breezy, and fast. With Devii, you can slice the API development process down from days to mere minutes. 

With Devii’s Instant API Engine, you can easily create a working GraphQL API and begin fetching data ASAP. Our Instant API engine connects to existing databases, automatically generates GraphQL schemas, and delivers the data you need quickly so you don't have to write a line of code. Need to add a table or a new column? No problem, Devii rewrites your Schema and resolvers in seconds. 

The GraphQL schemas include a regular, standardized set of parameters which offer robust and complex filtering, ordering, and paging of queries, as well as automatically generated mutations to create, update, and delete records. Plus, Devii offers a built-in user and group (“role”) management system, independent of the database schemas themselves.

By automating API generation, Devii provides built-in user management, enforces security policies, offers programmable server-side extensibility, and even automatically generates client-side data models for web applications. It’s API management, made simple.

Are you ready to level up your API management? Get started with Devii and book a free demo today.

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