Union types in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Union type in GraphQL?

A Union type in GraphQL lets a field return one of several different object types. It helps when a query can return different shapes of data.

beginner

How do you define a Union type in GraphQL schema?

Use the union keyword followed by the union name and the possible types separated by |. For example: union SearchResult = Photo | Person

intermediate

Can Union types include scalar types like String or Int?

No, Union types can only include object types, not scalar types like String or Int.

intermediate

How do you query a field that returns a Union type?

You use inline fragments with ... on TypeName to specify fields for each possible type in the union.

advanced

Why use Union types instead of Interfaces in GraphQL?

Union types are for when the types don’t share fields. Interfaces require shared fields. Use Union when types are different and unrelated.

Which keyword defines a Union type in GraphQL?

A enum

B interface

C union

D type

The union keyword is used to define a Union type in GraphQL.

Can a Union type include scalar types like Int or String?

A No, only object types

B Yes, always

C Only if wrapped in an object

D Only in mutations

Union types can only include object types, not scalar types.

How do you specify fields for each type in a Union when querying?

A Using variables

B Using fragments with fragment keyword only

C Using aliases

D Using inline fragments with ... on TypeName

Inline fragments with ... on TypeName let you select fields for each type in a Union.

What is a key difference between Union types and Interfaces?

A Union types do not require shared fields

B Interfaces can include scalar types

C Union types require shared fields

D Interfaces cannot be queried

Union types do not require shared fields, unlike Interfaces which do.

Which of these is a valid Union type definition?

A union Result = String | Int

B union Result = Photo | Person

C union Result = interface Person

D union Result = enum Status

Union types can only include object types like Photo and Person, not scalars or enums.

Explain what a Union type is in GraphQL and how it differs from an Interface.

Think about when you want to return different shapes of data without common fields.

Describe how to query a field that returns a Union type and why inline fragments are needed.

Imagine you get different objects and want to ask for their specific details.