What are non-null constraints in GraphQL?

Overview

All types in the GraphQL system are **nullable** by default. This means that a type like integer can not only take a number, including `1, 2, 3,...`, as its value but also take `null`, which means no values. At the same time, GraphQL also allows us to make any type **non-null**. This means that the types we make non-null will never return `null`. We always provide some values to the non-null types in GraphQL.

When to use

When we want to ensure that a particular field always exists, we use **non-null constraints**. It is important to remember that using a non-null field may make it more difficult to extend our GraphQL schema.

How non-null works

Let’s look at an example. In the following schema, we have a `Hotel` type with a `hotelLocation` field that refers to a `Location` type: 
type Hotel {
  hotelName: String!
  rating: Int!
  hotelLocation: Location!
}
type Location {
  address: String!
}
type Query {
  hotel(query: String): [Hotel]
}

Non-null fields are those that have an exclamation mark (!) next to their type. When we query these fields, they will not return a null value. Here’s a query:

hotel {
    hotelName
    hotelLocation {
      address
    }
  }

We can get the following outcomes:

// no restaurants exist
{ hotels: null } 
// all data present
{
  hotels: [{
    hotelName: "pearl continental",
    hotelLocation: {
      address: "Street 85, San Francisco"
    }
  }]
}

However, we will not be able to obtain the following outcomes:

// hotelName or hotelLocation not be null
// this result would be incorrect
{
  hotel: [{
    hotelName: null,
    hotelLocation: null
  }]
}

To ensure the structure of the response, GraphQL may also ensure the presence of specific fields when queried.

Unlock your potential: GraphQL series, all in one place!

To continue your exploration of GraphQL, check out our series of Answers below:

Free AI Mock Interviews
Coding Interview
Coding PatternsFree Interview
Gain insights and practical experience with coding patterns through targeted MCQs and coding problems, designed to match and challenge your expertise level.
System Design
YouTubeFree Interview
Learn to design a video streaming platform like YouTube by tackling functional and non-functional requirements, core components, and high-level to detailed design challenges.

Free Resources

Copyright ©2025 Educative, Inc. All rights reserved