Required fields with non-null (!) in GraphQL - Step-by-Step Execution

Concept Flow - Required fields with non-null (!)

Define field with !

↓

Field is required

↓

Client must provide value

↓

Server validates input

↓

If null or missing -> Error

↓

If valid -> Proceed

This flow shows how a GraphQL input field marked with ! is required, meaning clients must provide a non-null value or the server returns an error.

Execution Sample

GraphQL

input UserInput {
  id: ID!
  name: String!
  email: String
}

type User {
  id: ID!
}

type Mutation {
  createUser(input: UserInput!): User!
}

mutation {
  createUser(input: {id: "123", name: "John", email: "[e-mail]"}) {
    id
  }
}

# Invalid example (would error):
# mutation {
#   createUser(input: {id: "123"}) { id }
# }

This mutation requires an input object with required 'id' and 'name' fields (non-null), and an optional 'email' field.

Execution Table

Step	Field	Value Provided	Validation Result	Action
1	id	"123"	Valid (non-null)	Accept value
2	name	null or missing	Invalid (null not allowed)	Return error
3	email	null or missing	Valid (nullable)	Accept as null

💡 Execution stops with error if any required (!) field is null or missing.

Variable Tracker

Field	Start	After Validation	Final
id	undefined	"123"	"123"
name	undefined	null or missing	error triggered
email	undefined	null or missing	null accepted

Key Moments - 2 Insights

Why does the server return an error if a required field is missing or null?

Because fields marked with ! must have a non-null value. The execution_table row 2 shows that if 'name' is null or missing, validation fails and an error is returned.

Can a field without ! be null or missing without error?

Yes, as shown in execution_table row 3, 'email' is nullable and can be null or missing without causing an error.

Visual Quiz - 3 Questions

Look at the execution_table, what happens if the 'id' field is null?

A The server accepts it as null

B The server ignores the field

C The server returns an error

D The server replaces it with a default value

💡 Hint

Refer to execution_table row 1 where 'id' must be non-null or error occurs

At which step does the server detect a missing required field?

A Step 1

B Step 2

C Step 3

D After all fields are processed

💡 Hint

Check execution_table row 2 where 'name' is missing or null and triggers error

If the 'email' field is missing, what does the server do?

A Accepts null value

B Fills with default email

C Returns an error

D Ignores the entire user object

💡 Hint

See execution_table row 3 where 'email' is nullable and null is accepted

Concept Snapshot

GraphQL required input fields use ! after type.
This means the field cannot be null or missing in client input.
If client omits or sends null, server returns error.
Nullable fields (no !) can be null or missing safely.
Always provide values for ! fields in inputs/arguments.

Full Transcript

In GraphQL, input fields (in input types or arguments) marked with an exclamation mark (!) are required and must have a non-null value. When a client sends a query or mutation, the server checks these fields. If a required field is missing or null, the server returns an error and stops execution. Optional fields without ! can be null or missing without causing errors. This ensures data integrity by enforcing that important fields always have values.