Query arguments in GraphQL - Mini Project: Build & Apply

GraphQL Query Arguments

📖 Scenario: You are building a simple GraphQL API for a bookstore. You want to allow users to query for books by specifying arguments like id or author.

🎯 Goal: Create a GraphQL query that uses arguments to fetch specific books by id and by author.

📋 What You'll Learn

Define a Book type with fields id, title, and author.

Create a Query type with a bookById field that takes an id argument of type ID! and returns a Book.

Create a Query type with a booksByAuthor field that takes an author argument of type String! and returns a list of Book.

Write example queries using arguments to fetch a book by id and books by author.

💡 Why This Matters

🌍 Real World

GraphQL APIs often require arguments to fetch specific data, like searching for a book by its ID or author.

💼 Career

Understanding query arguments is essential for backend developers and API designers working with GraphQL to build flexible and efficient data queries.

1

Define the Book type

Create a GraphQL type called Book with fields id of type ID!, title of type String!, and author of type String!.

GraphQL

# Define the Book type with id, title, and author fields

Hint

Use the type keyword to define a new type. Each field needs a name and a type with an exclamation mark for required fields.

2

Add Query fields with arguments

Add a Query type with two fields: bookById that takes an id argument of type ID! and returns a Book, and booksByAuthor that takes an author argument of type String! and returns a list of Book.

GraphQL

type Book {
  id: ID!
  title: String!
  author: String!
}

# Add Query type with bookById and booksByAuthor fields with arguments

Hint

Define the Query type with fields that accept arguments inside parentheses. Use square brackets [] to indicate a list return type.

3

Write a query to fetch a book by id

Write a GraphQL query named GetBookById that calls bookById with an argument id set to "1" and requests the id, title, and author fields.

GraphQL

type Book {
  id: ID!
  title: String!
  author: String!
}

type Query {
  bookById(id: ID!): Book
  booksByAuthor(author: String!): [Book]
}

# Write a query named GetBookById to fetch bookById with id "1"

Hint

Use the query keyword followed by the query name. Pass the argument inside parentheses and request the fields inside curly braces.

4

Write a query to fetch books by author

Write a GraphQL query named GetBooksByAuthor that calls booksByAuthor with an argument author set to "Jane Austen" and requests the id, title, and author fields for each book.

GraphQL

type Book {
  id: ID!
  title: String!
  author: String!
}

type Query {
  bookById(id: ID!): Book
  booksByAuthor(author: String!): [Book]
}

query GetBookById {
  bookById(id: "1") {
    id
    title
    author
  }
}

# Write a query named GetBooksByAuthor to fetch booksByAuthor with author "Jane Austen"

Hint

Similar to the previous query, but call booksByAuthor with the author argument and request the fields for each book in the list.

Practice

1. What is the purpose of query arguments in GraphQL?

easy

A. To write comments inside queries

B. To define new types in the schema

C. To specify exactly what data you want from the server

D. To create mutations for updating data

Solution

1. Step 1: Understand what query arguments do

   Query arguments allow you to tell the server exactly which data you want, like filtering or limiting results.

2. Step 2: Compare options to the purpose

   Only To specify exactly what data you want from the server describes specifying data in queries. Other options describe unrelated tasks.

3. Final Answer:

   To specify exactly what data you want from the server -> Option C

4. Quick Check:

   Query arguments = specify data [OK]

Hint: Arguments filter or limit data inside parentheses [OK]

Common Mistakes:

• Confusing arguments with schema definitions
• Thinking arguments create mutations
• Using arguments for comments

2. Which of the following is the correct syntax to pass an argument named id with value 5 to a GraphQL query field user?

easy

A. user(id: 5) { name }

B. user[id=5] { name }

C. user{id=5} { name }

D. user(id=5) { name }

Solution

1. Step 1: Recall GraphQL argument syntax

   Arguments go inside parentheses after the field name, with colon separating name and value.

2. Step 2: Check each option's syntax

   user(id: 5) { name } uses parentheses and colon correctly. Options B and C use brackets or braces incorrectly. user(id=5) { name } uses equals sign instead of colon.

3. Final Answer:

   user(id: 5) { name } -> Option A

4. Quick Check:

   Arguments use (name: value) syntax [OK]

Hint: Use parentheses and colon for arguments (name: value) [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Using equals sign instead of colon
• Placing arguments inside braces

3. Given the query { books(limit: 2) { title } } and a database with books titled 'A', 'B', 'C', what will the query return?

medium

A. [{ title: 'A' }, { title: 'B' }, { title: 'C' }]

B. [] (empty list)

C. Error: 'limit' is not a valid argument

D. [{ title: 'A' }, { title: 'B' }]

Solution

1. Step 1: Understand the limit argument

   The limit: 2 argument restricts the number of returned books to 2.

2. Step 2: Predict the returned data

   From books 'A', 'B', 'C', only the first two 'A' and 'B' will be returned.

3. Final Answer:

   [{ title: 'A' }, { title: 'B' }] -> Option D

4. Quick Check:

   limit: 2 returns 2 items [OK]

Hint: Limit argument restricts number of results [OK]

Common Mistakes:

• Assuming all items return ignoring limit
• Thinking limit causes error
• Expecting empty list when data exists

4. Identify the error in this GraphQL query: { users(age: 'twenty') { name } } assuming age expects an integer argument.

medium

A. The field name 'users' is invalid

B. The argument value should be an integer, not a string

C. Missing curly braces around the argument

D. The query is correct and will run without errors

Solution

1. Step 1: Check argument type requirements

   The age argument expects an integer, but the query passes a string 'twenty'.

2. Step 2: Identify the type mismatch error

   Passing a string instead of an integer causes a type error in GraphQL.

3. Final Answer:

   The argument value should be an integer, not a string -> Option B

4. Quick Check:

   Argument types must match schema [OK]

Hint: Match argument types exactly as defined [OK]

Common Mistakes:

• Passing strings instead of numbers
• Assuming field names cause errors
• Thinking braces are needed around arguments

5. You want to query a list of products sorted by price descending and limited to 3 items. Which query correctly uses arguments to achieve this?

hard

A. { products(sortBy: "price_desc", limit: 3) { name price } }

B. { products(limit: 3, order: "desc") { name price } }

C. { products(sort: price, limit: 3) { name price } }

D. { products(limit: 3, sortBy: "desc_price") { name price } }

Solution

1. Step 1: Identify correct argument names and values

   The argument sortBy with value "price_desc" clearly indicates sorting by price descending. The limit argument limits results to 3.

2. Step 2: Evaluate each option's correctness

   { products(sortBy: "price_desc", limit: 3) { name price } } uses both arguments correctly. { products(limit: 3, order: "desc") { name price } } uses 'order' which may be invalid. { products(sort: price, limit: 3) { name price } } uses 'sort' without quotes and no direction. { products(limit: 3, sortBy: "desc_price") { name price } } uses 'desc_price' which is not standard.

3. Final Answer:

   { products(sortBy: "price_desc", limit: 3) { name price } } -> Option A

4. Quick Check:

   Use correct argument names and values [OK]

Hint: Use exact argument names and values from schema [OK]

Common Mistakes:

• Using wrong argument names like 'order' or 'sort'
• Passing unquoted values for strings
• Mixing argument order incorrectly