One-to-one relationships in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a one-to-one relationship field in GraphQL schema.

GraphQL

type User {
  id: ID!
  profile: [1]
}

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

AString

BProfile

C[Profile]

DInt

Attempts:

3 left

💡 Hint

Common Mistakes

Using a list type like [Profile] which implies one-to-many.

Using scalar types like String or Int instead of the related type.

The profile field should be of type Profile to represent a one-to-one relationship.

2fill in blank

medium

Complete the code to define the inverse one-to-one relationship field in the related type.

GraphQL

type Profile {
  id: ID!
  user: [1]
}

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

AUser

B[User]

CString

DID

Attempts:

3 left

💡 Hint

Common Mistakes

Using a list type which implies multiple users.

Using scalar types instead of the related object type.

The user field should be of type User to represent the one-to-one inverse relationship.

3fill in blank

hard

Fix the error in the GraphQL schema for one-to-one relationship by completing the field type.

GraphQL

type User {
  id: ID!
  profile: [1]
}

type Profile {
  id: ID!
  user: [User]
}

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

AProfile

B[Profile]

CString

DID

Attempts:

3 left

💡 Hint

Common Mistakes

Using list types which imply one-to-many relationships.

Using scalar types instead of object types.

The profile field in User must be Profile (not a list) to correctly represent a one-to-one relationship.

4fill in blank

hard

Fill both blanks to complete the GraphQL schema for a one-to-one relationship with non-nullable fields.

GraphQL

type User {
  id: ID!
  profile: [1]!
}

type Profile {
  id: ID!
  user: [2]!
}

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

AProfile

B[Profile]

CUser

D[User]

Attempts:

3 left

💡 Hint

Common Mistakes

Using list types which imply multiple related objects.

Omitting the non-nullable marker !.

Both sides use the related type without list brackets and are marked non-nullable with ! to enforce one-to-one.

5fill in blank

hard

Fill all three blanks to complete the GraphQL schema with one-to-one relationship and ID references.

GraphQL

type User {
  id: [1]!
  profileId: [2]
  profile: [3]
}

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

AID

BString

CProfile

DInt

Attempts:

3 left

💡 Hint

Common Mistakes

Using scalar types like String or Int for IDs inconsistently.

Using list types for the related object.

The id and profileId fields use ID type, and profile field uses the related Profile type.

Practice

1. What does a one-to-one relationship in GraphQL represent?

easy

A. Each item in one type is linked to exactly one item in another type.

B. Each item in one type can link to many items in another type.

C. Items are not linked between types.

D. One item links to zero or many items in the same type.

Solution

1. Step 1: Understand relationship types

   One-to-one means each item in one set matches exactly one item in another set.

2. Step 2: Apply to GraphQL context

   In GraphQL, this means a field in one type points to exactly one item in another type.

3. Final Answer:

   Each item in one type is linked to exactly one item in another type. -> Option A

4. Quick Check:

   One-to-one = single matching pair [OK]

Hint: One-to-one means exactly one match per item [OK]

Common Mistakes:

• Confusing one-to-one with one-to-many
• Thinking items can link to multiple items
• Assuming no links exist

2. Which of the following is the correct GraphQL syntax to define a one-to-one relationship between User and Profile types?

easy

A. type User { profile: String }

B. type User { profiles: [Profile] }

C. type User { profile: [Profile] }

D. type User { profile: Profile }

Solution

1. Step 1: Identify one-to-one field type

   One-to-one means a single object, so the field should be of type Profile, not a list.

2. Step 2: Check syntax correctness

   type User { profile: Profile } uses profile: Profile, which is correct syntax for one-to-one.

3. Final Answer:

   type User { profile: Profile } -> Option D

4. Quick Check:

   Single object field = one-to-one [OK]

Hint: Use single type, not list, for one-to-one fields [OK]

Common Mistakes:

• Using list syntax for one-to-one
• Using wrong field type like String
• Missing colon or braces

3. Given the schema:

type User { id: ID! name: String profile: Profile }

type Profile { id: ID! bio: String }

And the query:

{ user(id: "1") { name profile { bio } } }

If user with id "1" has name "Alice" and profile bio "Loves cats", what is the expected output?

medium

A. { "data": { "user": { "name": "Alice", "profile": { "bio": "Loves cats" } } } }

B. { "data": { "user": { "name": "Alice", "profile": null } } }

C. { "data": { "user": { "name": "Alice" } } }

D. Error: profile field missing

Solution

1. Step 1: Understand query fields

   The query requests user's name and profile's bio.

2. Step 2: Match data to query

   User "Alice" has a profile with bio "Loves cats", so both fields return data.

3. Final Answer:

   { "data": { "user": { "name": "Alice", "profile": { "bio": "Loves cats" } } } } -> Option A

4. Quick Check:

   Query fields match data output [OK]

Hint: Returned data matches requested fields exactly [OK]

Common Mistakes:

• Assuming profile is null when data exists
• Omitting nested profile field
• Expecting error when schema is correct

4. Identify the error in this GraphQL schema for one-to-one relationship:

type User { id: ID! profile: [Profile] }

type Profile { id: ID! user: User }

medium

A. User type must not have profile field.

B. Using list syntax [Profile] for one-to-one relationship is incorrect.

C. Missing exclamation mark after Profile.

D. Profile type cannot reference User.

Solution

1. Step 1: Check field type for one-to-one

   One-to-one means a single object, not a list. Using [Profile] means many profiles.

2. Step 2: Confirm correct syntax

   Field should be profile: Profile without brackets for one-to-one.

3. Final Answer:

   Using list syntax [Profile] for one-to-one relationship is incorrect. -> Option B

4. Quick Check:

   List means many, not one [OK]

Hint: No brackets for one-to-one fields [OK]

Common Mistakes:

• Confusing one-to-one with one-to-many
• Adding unnecessary exclamation marks
• Thinking references are not allowed

5. You want to model a one-to-one relationship between Author and Biography in GraphQL. Which schema design ensures each author has exactly one biography and each biography belongs to exactly one author?

hard

A. type Author { id: ID! name: String biography: Biography } type Biography { id: ID! text: String }

B. type Author { id: ID! name: String biographies: [Biography]! } type Biography { id: ID! text: String author: Author }

C. type Author { id: ID! name: String biography: Biography! } type Biography { id: ID! text: String author: Author! }

D. type Author { id: ID! name: String biographyId: ID! } type Biography { id: ID! text: String }

Solution

1. Step 1: Check for required one-to-one fields

   Both Author and Biography have non-nullable fields pointing to each other, ensuring exactly one match.

2. Step 2: Validate mutual references

   Each Author has one Biography! and each Biography has one Author!, enforcing one-to-one.

3. Final Answer:

   type Author { id: ID! name: String biography: Biography! } type Biography { id: ID! text: String author: Author! } -> Option C

4. Quick Check:

   Mutual non-null fields = strict one-to-one [OK]

Hint: Use non-null mutual fields for strict one-to-one [OK]

Common Mistakes:

• Using lists instead of single objects
• Making fields nullable allowing missing links
• Not linking both types mutually