Query variables in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable for a GraphQL query.

GraphQL

query GetUser($id: [1]) { user(id: $id) { name } }

Drag options to blanks, or click blank then click option'

ABoolean

BString

CInt

DFloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number type like Int when the ID is a string.

Forgetting the dollar sign before the variable name.

The variable $id is declared as a String type because user IDs are usually strings.

2fill in blank

medium

Complete the code to pass a variable in the GraphQL query arguments.

GraphQL

query GetPost($postId: ID!) { post(id: [1]) { title content } }

Drag options to blanks, or click blank then click option'

ApostId

BpostID

Cid

D$postId

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name without the $ prefix.

Using a different variable name than declared.

Variables in GraphQL queries are referenced with a $ prefix, so $postId is correct.

3fill in blank

hard

Fix the error in the variable declaration for a required integer variable.

GraphQL

query GetComments($limit: [1]) { comments(limit: $limit) { text } }

Drag options to blanks, or click blank then click option'

AInt!

BInt

CString!

DBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the exclamation mark for a required variable.

Using the wrong type like String for a number.

The exclamation mark ! means the variable is required (non-null). Since limit is an integer and required, Int! is correct.

4fill in blank

hard

Fill both blanks to declare and use a Boolean variable in a query.

GraphQL

query GetTasks($completed: [1]) { tasks(completed: [2]) { id title } }

Drag options to blanks, or click blank then click option'

ABoolean!

BBoolean

C$completed

Dcompleted

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name without $ inside the query.

Declaring the variable without the exclamation mark when it is required.

The variable $completed is declared as a required Boolean with Boolean! and used with the $ prefix inside the query.

5fill in blank

hard

Fill all three blanks to declare a variable, use it in the query, and specify its type as a list of IDs.

GraphQL

query GetUsers($ids: [1]) { users([3]: [2]) { name email } }

Drag options to blanks, or click blank then click option'

A[ID!]

B$ids

Cids

DID

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use square brackets for list types.

Using the variable name without $ inside the query.

Mixing up the argument name and variable name.

The variable $ids is declared as a list of non-null IDs with [ID!]. Inside the query, the variable is used with $ids, and the argument name is ids.

Practice

1. What is the main purpose of using query variables in GraphQL?

easy

A. To create new types in the GraphQL schema

B. To define the schema of the GraphQL server

C. To store query results on the client side

D. To reuse the same query with different input values

Solution

1. Step 1: Understand what query variables do

   Query variables allow you to write a query once and provide different inputs each time you run it.

2. Step 2: Compare options with this purpose

   Only To reuse the same query with different input values describes reusing queries with different inputs, which matches the purpose of query variables.

3. Final Answer:

   To reuse the same query with different input values -> Option D

4. Quick Check:

   Query variables = reuse queries with different inputs [OK]

Hint: Variables let you change inputs without rewriting queries [OK]

Common Mistakes:

• Confusing variables with schema definitions
• Thinking variables store data permanently
• Mixing variables with client-side caching

2. Which of the following is the correct way to declare a variable in a GraphQL query?

easy

A. query getUser($id: ID!) { user(id: $id) { name } }

B. query getUser(id: $ID) { user(id: id) { name } }

C. query getUser($id) { user(id: id) { name } }

D. query getUser { user(id: $id) { name } }

Solution

1. Step 1: Identify correct variable syntax

   Variables must be declared with a $ sign and a type, e.g., $id: ID! inside parentheses after the query name.

2. Step 2: Check each option

   query getUser($id: ID!) { user(id: $id) { name } } correctly declares $id: ID! and uses $id inside the query. Others miss type, $ sign, or parentheses.

3. Final Answer:

   query getUser($id: ID!) { user(id: $id) { name } } -> Option A

4. Quick Check:

   Variable declaration = $name: Type! in parentheses [OK]

Hint: Variables need $ and type declared after query name [OK]

Common Mistakes:

• Omitting the variable type
• Using variable without $ inside query
• Not placing variables in parentheses after query name

3. Given the query:

query getBook($bookId: ID!) { book(id: $bookId) { title author } }

and variables:

{ "bookId": "123" }

What will the query return if the book with ID 123 has title "GraphQL Guide" and author "Anna"?

medium

A. { "data": { "book": null } }

B. { "data": { "book": { "title": "GraphQL Guide", "author": "Anna" } } }

C. SyntaxError: Variable not defined

D. { "errors": [ { "message": "Book not found" } ] }

Solution

1. Step 1: Understand the query and variables

   The query asks for a book by ID using variable $bookId. The variable value is "123".

2. Step 2: Match variable value to data

   The book with ID "123" exists with title "GraphQL Guide" and author "Anna". So the query returns this data.

3. Final Answer:

   { "data": { "book": { "title": "GraphQL Guide", "author": "Anna" } } } -> Option B

4. Quick Check:

   Variable value matches book data = correct result [OK]

Hint: Variables fill query inputs to get matching data [OK]

Common Mistakes:

• Assuming variable names are optional
• Expecting errors when data exists
• Confusing null with errors

4. Identify the error in this GraphQL query using variables:

query getUser($userId: ID) { user(id: userId) { name } }

medium

A. Variable userId inside query should have a $ sign

B. Variable $userId is missing the non-null type indicator

C. Variables must be declared outside the query

D. Query name cannot have variables declared

Solution

1. Step 1: Check variable usage inside query

   The variable is declared as $userId but inside the query it is used as userId without the $ sign.

2. Step 2: Correct usage of variables

   Variables must be referenced with the $ sign inside the query fields, so it should be id: $userId.

3. Final Answer:

   Variable userId inside query should have a $ sign -> Option A

4. Quick Check:

   Use $ before variable inside query fields [OK]

Hint: Always use $ before variable inside query body [OK]

Common Mistakes:

• Forgetting $ before variable in query
• Thinking variables declared outside query
• Confusing variable declaration syntax

5. You want to write a GraphQL query to fetch a list of books filtered by optional author name using variables. Which query correctly declares the variable and uses it to filter books only if the variable is provided?

hard

A. query getBooks($author: String!) { books(author: $author) { title } }

B. query getBooks { books(author: $author) { title } }

C. query getBooks($author: String) { books(author: $author) { title } }

D. query getBooks($author) { books(author: author) { title } }

Solution

1. Step 1: Understand optional variable declaration

   To make a variable optional, declare it without the exclamation mark, e.g., $author: String.

2. Step 2: Check variable usage in query

   Use $author inside the query to filter books. query getBooks($author: String) { books(author: $author) { title } } correctly declares and uses the optional variable.

3. Step 3: Review other options

   query getBooks($author: String!) { books(author: $author) { title } } makes variable required with !, C uses variable without declaration, D misses type and uses variable incorrectly.

4. Final Answer:

   query getBooks($author: String) { books(author: $author) { title } } -> Option C

5. Quick Check:

   Optional variable = no ! and use $ in query [OK]

Hint: Optional variables omit ! and use $ inside query [OK]

Common Mistakes:

• Making optional variables required with !
• Using variables without declaration
• Forgetting $ in query usage