Inline fragments in GraphQL - Mini Project: Build & Apply

Using Inline Fragments in GraphQL Queries

📖 Scenario: You are building a GraphQL query to fetch data about different types of media items in a library. The library contains Books and Movies. Each type has some common fields and some unique fields.For example, both Books and Movies have id and title. Books have author and pageCount, while Movies have director and duration.

🎯 Goal: Create a GraphQL query that fetches the id and title for all media items, and uses inline fragments to fetch the specific fields for Books and Movies.

📋 What You'll Learn

Create a query named GetMediaItems

Fetch id and title for all media items

Use inline fragments to fetch author and pageCount for Books

Use inline fragments to fetch director and duration for Movies

💡 Why This Matters

🌍 Real World

GraphQL APIs often return data from interfaces or unions where different types share some fields but also have unique fields. Inline fragments let you fetch the right fields for each type in one query.

💼 Career

Understanding inline fragments is essential for working with GraphQL APIs in frontend or backend development, enabling you to write efficient and precise queries.

1

Create the base query for media items

Write a GraphQL query named GetMediaItems that fetches the id and title fields from mediaItems.

GraphQL

query GetMediaItems {
  mediaItems {
    id
    title
  }
  # Your code here
}

Hint

Start by writing a query that fetches the common fields id and title for all media items.

2

Add inline fragment for Books

Inside the mediaItems field, add an inline fragment for Book that fetches the author and pageCount fields.

GraphQL

query GetMediaItems {
  mediaItems {
    id
    title
    ... on Book {
      author
      pageCount
    }
    # Your code here
  }
}

Hint

Use ... on Book { author pageCount } inside mediaItems to fetch book-specific fields.

3

Add inline fragment for Movies

Inside the mediaItems field, add an inline fragment for Movie that fetches the director and duration fields.

GraphQL

query GetMediaItems {
  mediaItems {
    id
    title
    ... on Book {
      author
      pageCount
    }
    ... on Movie {
      director
      duration
    }
    # Your code here
  }
}

Hint

Use ... on Movie { director duration } inside mediaItems to fetch movie-specific fields.

4

Complete the query with all inline fragments

Ensure the query GetMediaItems fetches id and title for all media items, and uses inline fragments for Book and Movie to fetch their specific fields.

GraphQL

query GetMediaItems {
  mediaItems {
    id
    title
    ... on Book {
      author
      pageCount
    }
    ... on Movie {
      director
      duration
    }
    # Your code here
  }
}

Hint

Review your query to make sure all parts are included and correctly structured.

Practice

1. What is the main purpose of using inline fragments in a GraphQL query?

easy

A. To select fields conditionally based on the object type in a mixed list

B. To create new types in the schema

C. To update data on the server

D. To paginate query results

Solution

1. Step 1: Understand inline fragments usage

   Inline fragments allow querying different fields depending on the type of an object in a list or union.

2. Step 2: Identify the purpose in queries

   This lets you get specific fields for each type without separate queries.

3. Final Answer:

   To select fields conditionally based on the object type in a mixed list -> Option A

4. Quick Check:

   Inline fragments = conditional fields by type [OK]

Hint: Inline fragments pick fields by type inside mixed lists [OK]

Common Mistakes:

• Thinking inline fragments create new types
• Confusing inline fragments with mutations
• Using inline fragments for pagination

2. Which of the following is the correct syntax for an inline fragment in GraphQL?

easy

A. ... on { TypeName field1 field2 }

B. ... TypeName { field1 field2 }

C. ... TypeName on { field1 field2 }

D. ... on TypeName { field1 field2 }

Solution

1. Step 1: Recall inline fragment syntax

   The correct syntax uses three dots, then on, then the type name, followed by fields in braces.

2. Step 2: Match options to syntax

   ... on TypeName { field1 field2 } matches this exactly: ... on TypeName { field1 field2 }.

3. Final Answer:

   ... on TypeName { field1 field2 } -> Option D

4. Quick Check:

   Inline fragment syntax = '... on TypeName { fields }' [OK]

Hint: Remember: three dots + 'on' + type name + braces [OK]

Common Mistakes:

• Omitting the 'on' keyword
• Placing type name inside braces incorrectly
• Using wrong order of keywords

3. Given this GraphQL query snippet:

{
  searchItems {
    id
    ... on Book {
      author
    }
    ... on Movie {
      director
    }
  }
}

What fields will be returned for an item of type Movie?

medium

A. id and director

B. id and author

C. only director

D. only id

Solution

1. Step 1: Identify fields outside and inside fragments

   The field id is always returned for all items. For Movie type, the inline fragment selects director.

2. Step 2: Combine fields for Movie type

   So, the result for a Movie item includes id and director.

3. Final Answer:

   id and director -> Option A

4. Quick Check:

   Movie fields = id + director [OK]

Hint: Fields outside fragments always return; inside depends on type [OK]

Common Mistakes:

• Assuming author field returns for Movie
• Ignoring fields outside fragments
• Thinking only fragment fields return

4. Consider this GraphQL query:

{
  items {
    ... on Book {
      title
      author
    }
    ... on Movie {
      title
      director
    }
  }
}

What is the error in this query?

medium

A. Cannot query both Book and Movie in the same query

B. Missing closing brace for the root field

C. Fields inside fragments must be unique across fragments

D. Inline fragments cannot be used without a type condition

Solution

1. Step 1: Check query braces

   The query opens braces for items and two inline fragments but does not close the items field or the root query braces.

2. Step 2: Identify missing closing braces

   Proper GraphQL syntax requires matching closing braces for all opened braces.

3. Final Answer:

   Missing closing brace for the root field -> Option B

4. Quick Check:

   All braces must close properly [OK]

Hint: Count opening and closing braces carefully [OK]

Common Mistakes:

• Forgetting to close braces
• Thinking inline fragments need unique fields
• Believing you cannot query multiple types

5. You have a GraphQL schema with a union type SearchResult = Book | Movie | Author. You want to query a list of searchResults and get the title for Book, director for Movie, and name for Author. Which query correctly uses inline fragments to achieve this?

hard

A. { searchResults { ... { title director name } } }

B. { searchResults { title director name } }

C. { searchResults { ... on Book { title } ... on Movie { director } ... on Author { name } } }

D. { searchResults { ... on SearchResult { title director name } } }

Solution

1. Step 1: Understand union type querying

   For a union, you must use inline fragments with ... on TypeName to get fields specific to each type.

2. Step 2: Evaluate each option

   { searchResults { ... on Book { title } ... on Movie { director } ... on Author { name } } } correctly uses inline fragments for each type. { searchResults { title director name } } tries to get all fields directly, which fails. { searchResults { ... { title director name } } } has invalid syntax. { searchResults { ... on SearchResult { title director name } } } incorrectly uses the union name as a type condition.

3. Final Answer:

   { searchResults { ... on Book { title } ... on Movie { director } ... on Author { name } } } -> Option C

4. Quick Check:

   Use inline fragments per type in unions [OK]

Hint: Use '... on TypeName' for each union member [OK]

Common Mistakes:

• Querying all fields without fragments on unions
• Using union name as type condition
• Incorrect fragment syntax