Validation errors in GraphQL - Step-by-Step Execution

Concept Flow - Validation errors

Start Query Input

↓

Parse Query

↓

Check Syntax

↓

Validate Fields

↓

Validate Types

Yes↓

Check Authorization

↓

Execute Query

↓

Return Data or Validation Errors

The flow shows how a GraphQL query is checked step-by-step for syntax, field validity, type correctness, and authorization before execution or returning errors.

Execution Sample

GraphQL

query GetUser {
  user(id: "abc") {
    name
    age
  }
}

This query requests the name and age of a user with id 'abc'. Validation checks if 'user' field exists and if 'id' argument is correct.

Execution Table

Step	Action	Check/Evaluation	Result	Next Step
1	Parse Query	Is syntax valid?	Yes	Validate Fields
2	Validate Fields	Does 'user' field exist?	Yes	Validate Types
3	Validate Types	Is 'id' argument type String?	Yes	Check Authorization
4	Check Authorization	Is user authorized to query 'user'?	Yes	Execute Query
5	Execute Query	Fetch user data with id 'abc'	Data found	Return Data
6	Return Data	Send data back to client	Success	End

💡 Query passes all validations and returns requested data.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
querySyntaxValid	undefined	true	true	true	true	true
fieldExists	undefined	undefined	true	true	true	true
argumentTypeValid	undefined	undefined	undefined	true	true	true
authorized	undefined	undefined	undefined	undefined	true	true
executionResult	undefined	undefined	undefined	undefined	undefined	data

Key Moments - 3 Insights

Why does the validation stop if the syntax is incorrect?

Because as shown in step 1 of the execution_table, if syntax is invalid, the query cannot be parsed properly, so no further validation can happen.

What happens if the 'user' field does not exist in the schema?

Step 2 shows that if the field does not exist, validation fails and an error is returned before checking types or authorization.

Why is authorization checked after validating fields and types?

Authorization depends on knowing what fields and types are requested, so it happens after confirming the query is structurally correct (steps 2 and 3).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of step 3?

A 'id' argument type is valid

B Syntax error found

C User is unauthorized

D 'user' field does not exist

💡 Hint

Check the 'Result' column for step 3 in the execution_table.

At which step does the query execution actually happen?

A Step 2

B Step 5

C Step 4

D Step 6

💡 Hint

Look for the step labeled 'Execute Query' in the execution_table.

If the user is not authorized, which step returns an error?

A Step 5

B Step 3

C Step 4

D Step 6

💡 Hint

Check the 'Next Step' column after 'Check Authorization' in the execution_table.

Concept Snapshot

GraphQL Validation Errors Flow:
1. Parse query syntax
2. Validate fields exist
3. Check argument types
4. Verify authorization
5. Execute query if all pass
Errors stop execution early.

Full Transcript

This visual execution trace shows how a GraphQL query is validated step-by-step. First, the query syntax is checked. If syntax is valid, the fields requested are checked against the schema. Then, argument types are validated. After that, authorization is verified to ensure the user can access the data. If all validations pass, the query executes and returns data. If any validation fails, an error is returned immediately, stopping further processing.