Many-to-many relationships in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a many-to-many relationship between Author and Book types using GraphQL schema syntax.

GraphQL

type Author {
  id: ID!
  name: String!
  books: [[1]!]!
}

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

AString

BBook

CAuthor

DID

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong type like Author or scalar types instead of Book.

Not using a list to represent multiple books.

The books field in Author should be a list of Book types to represent the many-to-many relationship.

2fill in blank

medium

Complete the code to define the reciprocal many-to-many relationship from Book back to Author.

GraphQL

type Book {
  id: ID!
  title: String!
  authors: [[1]!]!
}

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

ABook

BString

CAuthor

DID

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong type like Book or scalar types instead of Author.

Not using a list to represent multiple authors.

The authors field in Book should be a list of Author types to link books back to their authors.

3fill in blank

hard

Fix the error in this GraphQL schema snippet that tries to define a many-to-many relationship but uses incorrect syntax.

GraphQL

type Author {
  id: ID!
  name: String!
  books: [1]
}

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

A[Book]!

B[Book]

CBook!

DBook

Attempts:

3 left

💡 Hint

Common Mistakes

Using just Book without list brackets.

Using [Book] without the non-null marker on the list.

The field books should be a non-null list of Book types, so [Book]! is correct.

4fill in blank

hard

Fill both blanks to complete the GraphQL schema for a join type AuthorBook that connects Author and Book by their IDs.

GraphQL

type AuthorBook {
  authorId: [1]!
  bookId: [2]!
}

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

AID

BString

CInt

DBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using String or Int instead of ID.

Using Boolean which is not suitable for IDs.

Both authorId and bookId should be of type ID to uniquely identify the related records.

5fill in blank

hard

Fill all three blanks to complete a GraphQL query that fetches authors with their books, filtering books by title containing 'GraphQL'.

GraphQL

query {
  authors {
    name
    books(filter: { title: { [1]: "GraphQL" } }) {
      [2]
      [3]
    }
  }
}

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

Acontains

Bid

Ctitle

Dequals

Attempts:

3 left

💡 Hint

Common Mistakes

Using equals instead of contains for filtering.

Not selecting both id and title fields.

The filter uses contains to find books with titles containing 'GraphQL'. The query selects id and title fields of those books.

Practice

1. In GraphQL, how do you represent a many-to-many relationship between two types, for example, Author and Book?

easy

A. By having a list of Book in Author and a list of Author in Book

B. By having a single field of Book in Author only

C. By using scalar fields only, no lists

D. By embedding Author inside Book as a string

Solution

1. Step 1: Understand many-to-many relationship in GraphQL

   Many-to-many means each Author can have many Books and each Book can have many Authors.

2. Step 2: Represent with lists on both types

   To model this, both Author and Book types should have a list field referencing the other type.

3. Final Answer:

   By having a list of Book in Author and a list of Author in Book -> Option A

4. Quick Check:

   Many-to-many = lists on both sides [OK]

Hint: Use lists on both types to link many items [OK]

Common Mistakes:

• Using a single object instead of a list
• Not linking both types with lists
• Using scalar fields instead of object references

2. Which of the following is the correct GraphQL schema snippet to define a many-to-many relationship between Student and Course?

easy

A. type Student { course: Course } type Course { student: Student }

B. type Student { courses: Course } type Course { students: Student }

C. type Student { courses: String } type Course { students: String }

D. type Student { courses: [Course!]! } type Course { students: [Student!]! }

Solution

1. Step 1: Check list syntax for many-to-many

   Many-to-many requires lists, so fields must be lists like [Course!]! and [Student!]!.

2. Step 2: Validate non-null and list usage

   type Student { courses: [Course!]! } type Course { students: [Student!]! } correctly uses non-null lists of non-null items, which is best practice.

3. Final Answer:

   type Student { courses: [Course!]! } type Course { students: [Student!]! } -> Option D

4. Quick Check:

   Lists with non-null = correct schema [OK]

Hint: Use square brackets for lists in GraphQL schema [OK]

Common Mistakes:

• Missing square brackets for lists
• Using singular fields instead of lists
• Using scalar types instead of object types

3. Given this GraphQL query on a many-to-many schema:

query { students { name courses { title } } }

What will the result include?

medium

A. A list of students with their names and a list of their enrolled courses' titles

B. Only student names without any course information

C. Only course titles without student names

D. An error because nested queries are not allowed

Solution

1. Step 1: Understand the query structure

   The query requests students with their name and nested courses with title.

2. Step 2: Interpret many-to-many data fetching

   Since courses is a list on Student, the result includes each student's name and their list of course titles.

3. Final Answer:

   A list of students with their names and a list of their enrolled courses' titles -> Option A

4. Quick Check:

   Nested lists fetch related data [OK]

Hint: Nested fields fetch linked many-to-many data [OK]

Common Mistakes:

• Expecting only flat data without nested lists
• Thinking nested queries cause errors
• Ignoring the many-to-many list structure

4. You wrote this GraphQL schema snippet:

type User { groups: Group } type Group { users: User }

Why does this cause problems in representing many-to-many relationships?

medium

A. Because the field names are incorrect

B. Because groups and users are not lists, so only one group or user can be linked

C. Because GraphQL does not allow circular references

D. Because the types are missing scalar fields

Solution

1. Step 1: Check field types for many-to-many

   Many-to-many requires lists on both sides, but here groups and users are single objects, not lists.

2. Step 2: Understand impact on data modeling

   This means each User can link to only one Group and vice versa, not many, so it breaks many-to-many.

3. Final Answer:

   Because groups and users are not lists, so only one group or user can be linked -> Option B

4. Quick Check:

   Lists needed for many-to-many [OK]

Hint: Use lists, not single objects, for many-to-many fields [OK]

Common Mistakes:

• Using single object fields instead of lists
• Assuming circular references cause errors
• Ignoring the need for lists in many-to-many

5. You have a many-to-many relationship between Artist and Album. You want to fetch all artists with their albums, but only include albums released after 2020. Which GraphQL query correctly applies this filter?

hard

A. query { artists { name albums { title releaseYear } where: { releaseYear > 2020 } } }

B. query { artists { name albums { title releaseYear filter: { releaseYear > 2020 } } } }

C. query { artists { name albums(where: { releaseYear_gt: 2020 }) { title releaseYear } } }

D. query { artists { name albums { title releaseYear } } filter: { releaseYear > 2020 } }

Solution

1. Step 1: Identify correct filter syntax in GraphQL

   GraphQL commonly uses arguments like where with conditions such as releaseYear_gt: 2020 to filter nested lists.

2. Step 2: Check query structure for filtering nested albums

   query { artists { name albums(where: { releaseYear_gt: 2020 }) { title releaseYear } } }

   correctly places the where argument inside the albums field to filter albums after 2020.

3. Final Answer:

   query { artists { name albums(where: { releaseYear_gt: 2020 }) { title releaseYear } } } -> Option C

4. Quick Check:

   Use where argument inside nested field [OK]

Hint: Apply filters as arguments inside nested fields [OK]

Common Mistakes:

• Placing filters outside nested fields
• Using invalid filter syntax
• Not filtering at the nested list level