Interfaces in GraphQL

1. Introduction

In GraphQL, interfaces allow you to define a common set of fields that multiple types can implement. This enables a powerful way to create flexible and reusable schemas.

2. Definition

An interface in GraphQL is a type that defines a set of fields that other object types must provide. An interface can be queried just like an object type, and it allows for polymorphic queries.

3. Usage of Interfaces

Interfaces are defined in the GraphQL schema language using the interface keyword. Types that implement an interface use the implements keyword.

• Define the interface
• Implement the interface in object types
• Query the interface

4. Code Example

Here is a simple example of how to define and use interfaces in GraphQL:

type Animal {
  name: String!
  age: Int!
}

interface Pet {
  name: String!
  age: Int!
}

type Dog implements Pet {
  name: String!
  age: Int!
  breed: String!
}

type Cat implements Pet {
  name: String!
  age: Int!
  color: String!
}

type Query {
  pets: [Pet!]!
}
                

In this example, Dog and Cat both implement the Pet interface, allowing them to be treated as Pet types in queries.

5. Best Practices

• Use interfaces to share common fields among types.
• Keep interface definitions concise and focused.
• Document the purpose of each interface clearly.

6. FAQ