Why Interface types in GraphQL? - Purpose & Use Cases

The Big Idea

What if you could ask for all pets in one simple question, no matter their kind?

The Scenario

Imagine you have different kinds of pets: dogs, cats, and birds. You want to list their names and ages, but each pet type has its own way of storing this information. Manually checking each pet type and writing separate code for each one becomes confusing and messy.

The Problem

Manually handling each pet type means writing repetitive code and constantly checking what kind of pet you have. This slows you down and makes mistakes easy, especially when you add new pet types later.

The Solution

Interface types let you define a common set of fields that all pet types share. This way, you can write one query that works for all pets, no matter their specific type, making your code cleaner and easier to maintain.

Before vs After

✗ Before

query {
  dogs { name age }
  cats { name age }
  birds { name age }
}

✓ After

query {
  pets { name age }
}

What It Enables

Interfaces enable you to treat different but related data types uniformly, simplifying queries and making your API flexible and scalable.

Real Life Example

A pet adoption website can use interface types to fetch basic info about all pets available, regardless if they are dogs, cats, or birds, showing a unified list to users.

Key Takeaways

Interfaces define shared fields for related types.

They reduce repetitive code and simplify queries.

They make APIs easier to extend and maintain.