Field-level permissions in GraphQL - Step-by-Step Execution

Concept Flow - Field-level permissions

Client sends GraphQL query

↓

Server checks user role

↓

Check each requested field

↓

Is user allowed to access field?

No→Exclude field from response

Yes↓

Fetch field data

↓

Build response with allowed fields

↓

Send response to client

The server checks user permissions for each field in the query and only returns data for fields the user is allowed to see.

Execution Sample

GraphQL

query {
  user {
    id
    email
    salary
  }
}

A client requests user id, email, and salary fields; server filters fields based on permissions.

Execution Table

Step	Field	User Role	Permission Check	Action	Response Field Included
1	id	employee	allowed	fetch data	yes
2	email	employee	allowed	fetch data	yes
3	salary	employee	denied	exclude field	no
4	Build response	-	-	include allowed fields only	{id, email}
5	Send response	-	-	response sent to client	{id, email}

💡 All fields checked; salary excluded due to permission denial

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
responseFields	[]	[id]	[id, email]	[id, email]	[id, email]

Key Moments - 2 Insights

Why is the salary field not included in the response even though it was requested?

Because the permission check at step 3 denied access for the 'employee' role, so the field was excluded from the response as shown in the execution_table.

Does the server fetch data for fields the user is not allowed to see?

No, as shown in step 3 of the execution_table, the server excludes denied fields before fetching data to protect sensitive information.

Visual Quiz - 3 Questions

Look at the execution_table, which fields are included in the final response?

A email and salary

B id and salary

C id and email

D id, email, and salary

💡 Hint

Check the 'Response Field Included' column in rows 4 and 5 of the execution_table.

At which step does the server decide to exclude the salary field?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Permission Check' and 'Action' columns for the salary field in the execution_table.

If the user role was 'admin' with permission to see salary, how would the responseFields variable change after step 3?

A [id, email]

B [id, email, salary]

C [salary]

D []

💡 Hint

Refer to variable_tracker and imagine salary is allowed and included after step 3.

Concept Snapshot

Field-level permissions check each requested field against user roles.
Only allowed fields are fetched and included in the response.
Denied fields are excluded to protect sensitive data.
This happens dynamically per query.
Ensures fine-grained access control in GraphQL APIs.

Full Transcript

Field-level permissions in GraphQL work by checking each field requested in a query against the user's role permissions. The server examines each field and decides if the user can access it. If allowed, the server fetches the data for that field; if denied, the field is excluded from the response. For example, if an employee requests id, email, and salary fields, but salary is restricted, the server returns only id and email. This process protects sensitive information by enforcing access control at the field level dynamically for every query.

Practice

1. What is the main purpose of field-level permissions in GraphQL?

easy

A. To cache query results

B. To control access to individual data fields

C. To define the schema structure

D. To speed up query execution

Solution

1. Step 1: Understand the concept of field-level permissions

   Field-level permissions restrict who can see or edit specific fields in data, protecting sensitive information.

2. Step 2: Identify the main purpose

   The main goal is to control access to individual data fields, not to speed up queries or define schema structure.

3. Final Answer:

   To control access to individual data fields -> Option B

4. Quick Check:

   Field-level permissions = control access [OK]

Hint: Focus on access control for each field, not overall schema [OK]

Common Mistakes:

• Confusing permissions with schema design
• Thinking it speeds up queries
• Assuming it caches data

2. Which of the following is the correct way to apply a field-level permission directive in a GraphQL schema?

easy

A. type User { email: String @auth(role: "admin") }

B. type User { email: String auth(role: "admin") }

C. type User { email: String @auth[role="admin"] }

D. type User { email: String #auth(role: "admin") }

Solution

1. Step 1: Recall GraphQL directive syntax

   Directives use the @directiveName(arguments) format placed after the field type.

2. Step 2: Match the correct syntax

   type User { email: String @auth(role: "admin") } uses @auth(role: "admin") correctly. Options A, B, and D have syntax errors or wrong symbols.

3. Final Answer:

   type User { email: String @auth(role: "admin") } -> Option A

4. Quick Check:

   Directive syntax = @name(args) [OK]

Hint: Remember directives start with @ and use parentheses [OK]

Common Mistakes:

• Omitting the @ symbol
• Using brackets [] instead of parentheses ()
• Commenting out the directive

3. Given this GraphQL query and schema with field-level permissions:

type User { id: ID! name: String email: String @auth(role: "admin") }

If a user with role "user" runs:

{ user { id name email } }

What will be the result?

medium

A. { "data": { "user": { "id": "1", "name": "Alice", "email": "[e-mail]" } } }

B. { "data": { "user": { "id": "1", "name": "Alice", "email": null } } }

C. Error: Unauthorized to access field 'email'

D. { "data": { "user": { "id": "1", "name": "Alice" } } }

Solution

1. Step 1: Understand the permission on the email field

   The @auth(role: "admin") directive restricts email access to admin role only.

2. Step 2: Predict query result for a user role

   The user role is not admin, so email field is omitted from the response, not returned as null or error.

3. Final Answer:

   { "data": { "user": { "id": "1", "name": "Alice" } } } -> Option D

4. Quick Check:

   Unauthorized fields are omitted, not null or error [OK]

Hint: Unauthorized fields are hidden, not null or error [OK]

Common Mistakes:

• Expecting null instead of omitted field
• Expecting an error response
• Assuming all fields return regardless of role

4. You wrote this schema snippet:

type User { id: ID! name: String email: String @auth(role: admin) }

Why does this cause an error when applying field-level permissions?

medium

A. The role value admin should be a string in quotes

B. The @auth directive is not allowed on fields

C. ID! type cannot have directives

D. The email field must be nullable to use permissions

Solution

1. Step 1: Check the directive argument syntax

   Directive arguments must be valid GraphQL values; strings require quotes.

2. Step 2: Identify the error in role argument

   The role value admin is unquoted, causing a syntax error. It should be "admin".

3. Final Answer:

   The role value admin should be a string in quotes -> Option A

4. Quick Check:

   Directive args strings need quotes [OK]

Hint: Always put string arguments in quotes inside directives [OK]

Common Mistakes:

• Forgetting quotes around string arguments
• Thinking directives can't be on fields
• Assuming non-null types disallow directives

5. You want to allow users to see their own email field but only admins to see others' emails. Which field-level permission setup achieves this?

hard

A. Use @auth(role: "admin") on email field only

B. Make email field public and filter in resolver

C. Use a custom directive checking if user is owner or admin

D. Remove email field from schema and add a separate query

Solution

1. Step 1: Analyze the requirement

   Users can see their own email; admins can see all emails. This needs conditional logic.

2. Step 2: Evaluate options for conditional access

   Use a custom directive checking if user is owner or admin uses a custom directive to check ownership or admin role, fitting the requirement precisely.

3. Step 3: Why other options fail

   Use @auth(role: "admin") on email field only restricts email only to admins, blocking users from their own email. Make email field public and filter in resolver exposes email publicly, unsafe. Remove email field from schema and add a separate query complicates schema unnecessarily.

4. Final Answer:

   Use a custom directive checking if user is owner or admin -> Option C

5. Quick Check:

   Conditional access needs custom logic [OK]

Hint: Use custom directives for complex permission logic [OK]

Common Mistakes:

• Using simple role checks only
• Exposing sensitive fields publicly
• Overcomplicating schema with extra queries