Search across types in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Search across types' mean in GraphQL?

It means querying multiple different data types in a single search, so you can find results from various categories or objects at once.

intermediate

How can you search across different types in GraphQL?

By using a union or interface type that groups multiple types together, then querying that union or interface to get results from all included types.

beginner

What is a GraphQL union type?

A union type lets you combine multiple object types into one, so a query can return different types of objects in the same field.

intermediate

Why use fragments when searching across types?

Fragments let you specify which fields to get from each type in a union or interface, so you get the right data for each kind of result.

intermediate

Example: How to write a query that searches across 'Book' and 'Author' types?

Use a union type like 'union SearchResult = Book | Author' and query it with fragments for each type to get fields like title for Book and name for Author.

What GraphQL feature allows combining multiple types for a single search?

A Input type

B Scalar type

C Union type

D Enum type

Union types let you combine multiple object types so a field can return different types.

When querying a union type, how do you specify fields for each type?

A Using fragments

B Using variables

C Using directives

D Using enums

Fragments let you define fields for each type inside a union or interface.

Which of these is NOT a valid use of searching across types?

A Getting user and product info together

B Returning only scalar values

C Finding books and authors in one query

D Searching multiple categories at once

Searching across types involves objects, not just scalar values.

What keyword defines a union type in GraphQL schema?

A enum

B interface

C type

D union

'union' keyword is used to define a union type.

Can you use interfaces instead of unions for searching across types?

A Yes, interfaces can also group types

B No, only unions work

C Only with scalar types

D Only in mutations

Interfaces can also group types and be used for searching across types.

Explain how to perform a search across multiple types in GraphQL.

Think about how to combine types and get fields from each.

Describe the difference between union types and interfaces when searching across types.

Consider how each groups types and what fields they require.

Practice

1. What does the __typename field do in a GraphQL query when searching across types?

easy

A. It tells you the type of each returned object in the result.

B. It filters the results to only one type.

C. It sorts the results alphabetically.

D. It limits the number of results returned.

Solution

1. Step 1: Understand the role of __typename

   The __typename field returns the name of the type of each object in the query result.

2. Step 2: Differentiate from other options

   It does not filter, sort, or limit results; it only identifies the type.

3. Final Answer:

   It tells you the type of each returned object in the result. -> Option A

4. Quick Check:

   __typename shows object type [OK]

Hint: Remember: __typename reveals object type, not filters or limits [OK]

Common Mistakes:

• Thinking __typename filters results
• Assuming it sorts or limits data
• Confusing it with field selection

2. Which of the following is the correct syntax to query two different types, Book and Author, in one GraphQL query using fragments?

easy

A. query { search { ... on Book { title } ... on Author { name } } }

B. query { search { Book { title } Author { name } } }

C. query { search { title, name } }

D. query { search { ...Book { title } ...Author { name } } }

Solution

1. Step 1: Recognize fragment syntax for multiple types

   Fragments use ... on TypeName { fields } to specify fields for each type.

2. Step 2: Check each option's syntax

   query { search { ... on Book { title } ... on Author { name } } } correctly uses inline fragments for Book and Author. Options B, C, and D have invalid syntax.

3. Final Answer:

   query { search { ... on Book { title } ... on Author { name } } } -> Option A

4. Quick Check:

   Fragments use ... on Type [OK]

Hint: Use ... on Type for each type's fields [OK]

Common Mistakes:

• Using type names as fields directly
• Omitting 'on' keyword in fragments
• Trying to list fields without fragments

3. Given this GraphQL query:

query { search { __typename ... on Book { title author } ... on Author { name booksCount } } }

What will be the output if the search returns one Book and one Author?

medium

A. [{ "title": "1984", "author": "Orwell" }, { "name": "Orwell", "booksCount": 5 }]

B. [{ "__typename": "Book", "title": "1984", "author": "Orwell" }, { "__typename": "Author", "name": "Orwell", "booksCount": 5 }]

C. [{ "__typename": "Book", "name": "1984", "author": "Orwell" }, { "__typename": "Author", "title": "Orwell", "booksCount": 5 }]

D. Error: Cannot query field 'booksCount' on type 'Author'

Solution

1. Step 1: Understand the query structure

   The query requests __typename and fields specific to Book and Author types.

2. Step 2: Match output to query

   The output includes type names and requested fields correctly matched to each object.

3. Final Answer:

   [{ "__typename": "Book", "title": "1984", "author": "Orwell" }, { "__typename": "Author", "name": "Orwell", "booksCount": 5 }] -> Option B

4. Quick Check:

   Output matches requested fields and types [OK]

Hint: Look for __typename and matching fields in output [OK]

Common Mistakes:

• Ignoring __typename in output
• Mixing fields between types
• Assuming syntax errors without cause

4. Identify the error in this GraphQL query that searches across types:

query { search { ... on Book { title author } ... on Author { name booksCount } } }

Assuming booksCount is not a valid field on Author type.

medium

A. The query will ignore the Author fragment entirely.

B. The query will succeed but return null for booksCount.

C. The query will fail because booksCount is not a valid field on Author.

D. The query syntax is invalid due to missing commas.

Solution

1. Step 1: Check field validity on types

   Since booksCount is not defined on Author, the query is invalid.

2. Step 2: Understand GraphQL error handling

   GraphQL returns an error and fails the query if a requested field does not exist on the type.

3. Final Answer:

   The query will fail because booksCount is not a valid field on Author. -> Option C

4. Quick Check:

   Invalid field causes query failure [OK]

Hint: Check if all fields exist on their types before querying [OK]

Common Mistakes:

• Assuming invalid fields return null
• Ignoring GraphQL schema validation errors
• Thinking commas are required between fragments

5. You want to search across three types: Book, Author, and Publisher. Each type has a field name, but Book also has pages, Author has birthYear, and Publisher has location. Which query correctly fetches the name for all types and their specific fields?

hard

A. query { search { ...Book { name pages } ...Author { name birthYear } ...Publisher { name location } } }

B. query { search { name pages birthYear location } }

C. query { search { __typename { name } ... on Book { pages } ... on Author { birthYear } ... on Publisher { location } } }

D. query { search { __typename ... on Book { name pages } ... on Author { name birthYear } ... on Publisher { name location } } }

Solution

1. Step 1: Use __typename to identify each type

   This helps distinguish which object is which type in the results.

2. Step 2: Use inline fragments with ... on Type syntax

   Each fragment fetches the common name and the type-specific fields.

3. Step 3: Verify syntax correctness

   query { search { __typename ... on Book { name pages } ... on Author { name birthYear } ... on Publisher { name location } } } correctly uses fragments and includes __typename. Other options have syntax errors or missing fragments.

4. Final Answer:

   query { search { __typename ... on Book { name pages } ... on Author { name birthYear } ... on Publisher { name location } } } -> Option D

5. Quick Check:

   Fragments + __typename fetch all fields correctly [OK]

Hint: Use __typename and fragments for each type's fields [OK]

Common Mistakes:

• Listing all fields without fragments
• Omitting __typename for type identification
• Incorrect fragment syntax without 'on'