Enum types in GraphQL - Step-by-Step Execution

Concept Flow - Enum types

Define Enum Type

↓

Use Enum in Schema

↓

Client Queries with Enum

↓

Server Validates Enum Value

↓

Return Data or Error

This flow shows how an Enum type is defined, used in schema, queried by client, validated by server, and then data or error is returned.

Execution Sample

GraphQL

enum Role {
  ADMIN
  USER
  GUEST
}

type Query {
  user(id: ID!): User
}

type User {
  role: Role
}

query GetUserRole {
  user(id: 1) {
    role
  }
}

Defines an Enum 'Role' with three values and queries a user's role using that Enum.

Execution Table

Step	Action	Input/Query	Validation	Result
1	Define Enum	Role: ADMIN, USER, GUEST	N/A	Enum type 'Role' created with 3 values
2	Use Enum in Schema	user.role: Role	N/A	Field 'role' expects one of Role Enum values
3	Client Query	query GetUserRole { user(id:1) { role } }	Check if 'role' value is in Enum	Valid query sent to server
4	Server Resolves Role	User role = ADMIN	ADMIN is in Role Enum	Returns role: ADMIN
5	Client Receives	role: ADMIN	N/A	Client gets role as 'ADMIN'
6	Client Query with Invalid Enum	query { user(id:2) { role } }	User role = SUPERADMIN (invalid)	Error: 'SUPERADMIN' not in Enum Role
7	End	N/A	N/A	Execution stops due to invalid Enum value

💡 Execution stops when an invalid Enum value is encountered during validation.

Variable Tracker

Variable	Start	After Step 4	After Step 6	Final
Role Enum	Not defined	Defined with ADMIN, USER, GUEST	No change	Defined with ADMIN, USER, GUEST
user.role	N/A	ADMIN (valid)	SUPERADMIN (invalid)	SUPERADMIN (invalid)

Key Moments - 2 Insights

Why does the server reject a role value not listed in the Enum?

Because the Enum type only allows predefined values (see execution_table step 6), any value outside those causes a validation error.

Can the client send any string as an Enum value in the query?

No, the client must send one of the Enum's defined values; otherwise, the server returns an error (execution_table step 6).

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the role value returned by the server?

A GUEST

B ADMIN

C USER

D SUPERADMIN

💡 Hint

Check the 'Result' column in step 4 of the execution_table.

At which step does the server detect an invalid Enum value?

A Step 6

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the step where validation fails in the execution_table.

If the Enum 'Role' included 'SUPERADMIN', what would change in the execution_table?

A Step 4 would fail validation

B Step 6 would return an error

C Step 6 would return role SUPERADMIN successfully

D No change

💡 Hint

Consider how validation depends on Enum values as shown in steps 4 and 6.

Concept Snapshot

Enum types define a fixed set of allowed values.
Use 'enum' keyword to declare.
Fields using Enum accept only these values.
Queries must use valid Enum values.
Server validates and rejects invalid values.
Helps keep data consistent and clear.

Full Transcript

Enum types in GraphQL are special types that list a set of allowed values. First, you define an Enum with the 'enum' keyword and list its values. Then you use this Enum in your schema for fields that should only accept those values. When a client queries such a field, the server checks if the value is one of the Enum's allowed values. If yes, it returns the value; if not, it returns an error. This ensures only valid, expected values are used, making data consistent and easier to understand.