Enum types in GraphQL - Mini Project: Build & Apply

GraphQL Enum Types for User Roles

📖 Scenario: You are building a user management system where each user has a specific role. Roles can be ADMIN, EDITOR, or VIEWER. You want to use GraphQL enum types to define these roles clearly in your schema.

🎯 Goal: Create a GraphQL schema that defines an enum type called UserRole with the values ADMIN, EDITOR, and VIEWER. Then use this enum type in a User type to specify the user's role.

📋 What You'll Learn

Define an enum type called UserRole with values ADMIN, EDITOR, and VIEWER.

Create a User type with fields id (ID!), name (String!), and role (UserRole!).

Add a query type users that returns a list of User objects.

💡 Why This Matters

🌍 Real World

Enum types in GraphQL help define fixed sets of options, like user roles, status codes, or categories, making APIs clearer and safer.

💼 Career

Understanding enums is essential for backend developers working with GraphQL APIs to enforce valid data and improve API design.

1

Define the UserRole enum type

Create a GraphQL enum type called UserRole with the values ADMIN, EDITOR, and VIEWER.

GraphQL

# Your code here
enum UserRole {
  ADMIN
  EDITOR
  VIEWER
}

Hint

Use the enum keyword followed by the enum name and list the values inside curly braces.

2

Create the User type using UserRole enum

Create a GraphQL type called User with fields id of type ID!, name of type String!, and role of type UserRole!.

GraphQL

enum UserRole {
  ADMIN
  EDITOR
  VIEWER
}

# Your code here
type User {
  id: ID!
  name: String!
  role: UserRole!
}

Hint

Define the User type with the specified fields and use the UserRole enum for the role field.

3

Add a users query returning a list of User

Add a Query type with a field called users that returns a list of User objects. Use the syntax [User!]! to indicate a non-null list of non-null users.

GraphQL

enum UserRole {
  ADMIN
  EDITOR
  VIEWER
}

type User {
  id: ID!
  name: String!
  role: UserRole!
}

# Your code here
type Query {
  users: [User!]!
}

Hint

Define the Query type with a users field that returns a list of User objects.

4

Complete the schema with schema definition

Add the schema definition specifying that the query root type is Query.

GraphQL

enum UserRole {
  ADMIN
  EDITOR
  VIEWER
}

type User {
  id: ID!
  name: String!
  role: UserRole!
}

type Query {
  users: [User!]!
}

# Your code here
schema {
  query: Query
}

Hint

Use the schema keyword to define the root query type.

Practice

1. What is the main purpose of using enum types in GraphQL schemas?

easy

A. To allow any string value for a field

B. To create a numeric range for a field

C. To define a list of objects

D. To restrict a field to a fixed set of allowed values

Solution

1. Step 1: Understand enum purpose

   Enums limit a field to specific predefined values, ensuring data consistency.

2. Step 2: Compare options

   Only To restrict a field to a fixed set of allowed values describes restricting values to a fixed set, which is the enum's role.

3. Final Answer:

   To restrict a field to a fixed set of allowed values -> Option D

4. Quick Check:

   Enum = fixed allowed values [OK]

Hint: Enums fix allowed values, not free text or ranges [OK]

Common Mistakes:

• Thinking enums allow any string
• Confusing enums with lists or objects
• Assuming enums define numeric ranges

2. Which of the following is the correct syntax to define an enum type Status with values ACTIVE and INACTIVE in GraphQL?

easy

A. enum Status: ACTIVE | INACTIVE

B. enum Status { ACTIVE INACTIVE }

C. enum Status = ["ACTIVE", "INACTIVE"]

D. type Status = enum { ACTIVE, INACTIVE }

Solution

1. Step 1: Recall GraphQL enum syntax

   GraphQL enums are defined using enum Name { VALUE1 VALUE2 } syntax.

2. Step 2: Check each option

   enum Status { ACTIVE INACTIVE } matches the correct syntax. Others use invalid or mixed syntax.

3. Final Answer:

   enum Status { ACTIVE INACTIVE } -> Option B

4. Quick Check:

   Correct enum syntax = enum Status { ACTIVE INACTIVE } [OK]

Hint: Enums use curly braces with values, no equals or brackets [OK]

Common Mistakes:

• Using equals sign or brackets for enums
• Confusing enum with type or array syntax
• Using colon or pipe symbols incorrectly

3. Given the enum definition:

enum Role { ADMIN USER GUEST }

and the query:

{ userRole }

where userRole returns ADMIN, what will be the output type of userRole?

medium

A. A boolean true

B. An integer representing ADMIN

C. "ADMIN" (a string matching enum value)

D. An error because ADMIN is not a string

Solution

1. Step 1: Understand enum value representation

   GraphQL enums return the enum value as a string matching one of the defined enum names.

2. Step 2: Analyze the query output

   The query returns ADMIN, which is output as the string "ADMIN".

3. Final Answer:

   "ADMIN" (a string matching enum value) -> Option C

4. Quick Check:

   Enum output = string value [OK]

Hint: Enum values output as strings, not numbers or booleans [OK]

Common Mistakes:

• Expecting numeric or boolean output
• Thinking enum values cause errors
• Confusing enum with custom object types

4. Consider this enum definition:

enum Color { RED GREEN BLUE }

Which of the following queries will cause a validation error?

medium

A. { favoriteColor(color: YELLOW) }

B. { favoriteColor(color: GREEN) }

C. { favoriteColor(color: RED) }

D. { favoriteColor(color: BLUE) }

Solution

1. Step 1: Check enum allowed values

   The enum Color allows only RED, GREEN, and BLUE.

2. Step 2: Identify invalid value

   { favoriteColor(color: YELLOW) } uses YELLOW, which is not in the enum, causing a validation error.

3. Final Answer:

   { favoriteColor(color: YELLOW) } -> Option A

4. Quick Check:

   Invalid enum value = validation error [OK]

Hint: Only use enum values defined exactly, others cause errors [OK]

Common Mistakes:

• Using values not in enum
• Ignoring case sensitivity in enum values
• Assuming enums accept any string

5. You want to add a new enum Priority with values LOW, MEDIUM, and HIGH to a GraphQL schema. You also want to ensure that a query tasksByPriority(priority: Priority) returns only tasks matching the selected priority. Which of the following schema snippets correctly defines the enum and query?

hard

A. enum Priority { LOW MEDIUM HIGH } type Query { tasksByPriority(priority: Priority): [Task] }

B. type Priority { LOW MEDIUM HIGH } type Query { tasksByPriority(priority: Priority): [Task] }

C. enum Priority = [LOW, MEDIUM, HIGH] type Query { tasksByPriority(priority: Priority): [Task] }

D. enum Priority { LOW, MEDIUM, HIGH } type Query { tasksByPriority(priority: Priority): Task }

Solution

1. Step 1: Define enum correctly

   enum Priority { LOW MEDIUM HIGH } type Query { tasksByPriority(priority: Priority): [Task] } uses correct enum syntax without commas: enum Priority { LOW MEDIUM HIGH }.

2. Step 2: Define query returning list of tasks

   The query returns a list [Task], matching multiple tasks by priority.

3. Step 3: Check other options

   type Priority { LOW MEDIUM HIGH } type Query { tasksByPriority(priority: Priority): [Task] } wrongly defines Priority as a type, not enum. enum Priority = [LOW, MEDIUM, HIGH] type Query { tasksByPriority(priority: Priority): [Task] } uses invalid enum syntax with equals and brackets. enum Priority { LOW, MEDIUM, HIGH } type Query { tasksByPriority(priority: Priority): Task } uses commas in enum and returns a single Task, not list.

4. Final Answer:

   enum Priority { LOW MEDIUM HIGH } type Query { tasksByPriority(priority: Priority): [Task] } -> Option A

5. Quick Check:

   Correct enum + list query = enum Priority { LOW MEDIUM HIGH } type Query { tasksByPriority(priority: Priority): [Task] } [OK]

Hint: Enums use braces without commas; queries return list with [Type] [OK]

Common Mistakes:

• Using commas inside enum definitions
• Defining enum as type instead of enum
• Returning single object instead of list for multiple results