Field selection in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is field selection in GraphQL?

Field selection is the process of specifying exactly which fields you want to get back from a GraphQL query. It helps you get only the data you need.

beginner

How do you select multiple fields in a GraphQL query?

You list the fields inside curly braces after the query or object name. For example:

{ name age }

selects the name and age fields.

beginner

Why is field selection useful in GraphQL?

It reduces the amount of data sent over the network by only fetching what you need. This makes apps faster and saves bandwidth.

intermediate

Can you select nested fields in GraphQL? How?

Yes. You select nested fields by adding another set of curly braces inside a field. For example:

{ user { name email } }

gets the name and email of the user.

intermediate

What happens if you request a field that does not exist in GraphQL?

The server returns an error saying the field is unknown. GraphQL only allows fields defined in the schema to be queried.

In GraphQL, how do you specify which fields to get in a query?

A By writing JavaScript functions

B By using SQL SELECT statements

C By setting HTTP headers

D By listing fields inside curly braces after the query name

GraphQL uses curly braces to specify which fields to select in a query.

What is the benefit of selecting only needed fields in GraphQL?

A It makes the server slower

B More data is always better

C Faster responses and less data transfer

D It disables caching

Selecting only needed fields reduces data size and speeds up responses.

How do you select nested fields in GraphQL?

A By adding curly braces inside a field selection

B By using dot notation like user.name

C By writing multiple queries

D By using SQL JOINs

Nested fields are selected by adding curly braces inside the parent field.

What happens if you query a field not defined in the GraphQL schema?

A The server returns an error

B The server ignores the field

C The server returns null

D The server adds the field automatically

GraphQL servers return an error if you request unknown fields.

Which of these is a valid GraphQL field selection?

A SELECT title, author FROM books

B { title author { name } }

C <title> <author>

D GET /books/title/author

GraphQL uses curly braces to select fields and nested fields.

Explain what field selection means in GraphQL and why it is important.

Think about how you ask for only what you need in a menu.

Describe how to select nested fields in a GraphQL query with an example.

Imagine asking for details inside a bigger object.

Practice

1. What does field selection in GraphQL allow you to do?

easy

A. Encrypt data before sending it

B. Automatically update the database schema

C. Choose only the data fields you want to receive

D. Create new database tables

Solution

1. Step 1: Understand the purpose of field selection

   Field selection lets you specify exactly which fields you want in your query response.

2. Step 2: Compare options with the concept

   Only Choose only the data fields you want to receive describes choosing specific data fields, which matches field selection.

3. Final Answer:

   Choose only the data fields you want to receive -> Option C

4. Quick Check:

   Field selection = Choose specific fields [OK]

Hint: Field selection means picking only needed data fields [OK]

Common Mistakes:

• Confusing field selection with schema changes
• Thinking it encrypts data
• Assuming it creates database tables

2. Which of the following is the correct GraphQL syntax to select the fields id and name from a user?

easy

A. { user: id, name }

B. { user(id, name) }

C. query user { id, name }

D. { user { id, name } }

Solution

1. Step 1: Recall GraphQL field selection syntax

   Fields are selected inside curly braces after the type name, separated by commas or spaces.

2. Step 2: Check each option's syntax

   { user { id, name } } correctly uses braces and field names inside user. Others have syntax errors or wrong structure.

3. Final Answer:

   { user { id, name } } -> Option D

4. Quick Check:

   Correct field selection syntax = { user { id, name } } [OK]

Hint: Use braces to nest fields inside the type name [OK]

Common Mistakes:

• Using colon instead of braces for fields
• Omitting braces around fields
• Trying to pass fields as function arguments

3. Given this GraphQL query:

{ book { title author { name } } }

What fields will be returned in the response?

medium

A. { "book": { "title": "...", "author": { "name": "..." } } }

B. { "book": { "title": "...", "author": "..." } }

C. { "book": { "author": { "name": "..." } } }

D. { "book": { "title": "..." } }

Solution

1. Step 1: Analyze the query structure

   The query requests title and nested author with its name field.

2. Step 2: Determine the response shape

   The response will include title and an author object containing name.

3. Final Answer:

   { "book": { "title": "...", "author": { "name": "..." } } } -> Option A

4. Quick Check:

   Nested fields return nested objects [OK]

Hint: Nested fields return nested objects in response [OK]

Common Mistakes:

• Expecting author as a string instead of object
• Missing requested fields in response
• Ignoring nested field structure

4. Identify the error in this GraphQL query:

{ user { id name, } }

medium

A. Trailing comma after last field causes syntax error

B. Missing parentheses after user

C. Fields must be quoted strings

D. Curly braces are not allowed inside queries

Solution

1. Step 1: Check field list syntax

   GraphQL does not allow a comma after the last field in a selection set.

2. Step 2: Verify other syntax rules

   No parentheses needed after user, fields are unquoted, and braces are required.

3. Final Answer:

   Trailing comma after last field causes syntax error -> Option A

4. Quick Check:

   No trailing commas in field lists [OK]

Hint: No trailing commas after last field in selection [OK]

Common Mistakes:

• Adding commas after last field
• Adding unnecessary parentheses
• Quoting field names

5. You want to fetch a list of products with only their id and price, but each product also has a nested manufacturer with name and location. How do you write a GraphQL query to select only id, price, and the manufacturer's name (not location)?

hard

A. { products { id price manufacturer { name location } } }

B. { products { id price manufacturer { name } } }

C. { products { id price manufacturer name } }

D. { products { id price, manufacturer: { name } } }

Solution

1. Step 1: Identify required fields

   We need id, price, and nested manufacturer with only name.

2. Step 2: Write correct nested field selection

   { products { id price manufacturer { name } } } correctly nests name inside manufacturer and excludes location.

3. Step 3: Check other options for errors

   { products { id price manufacturer { name location } } } includes unwanted location. { products { id price manufacturer name } } incorrectly places name outside manufacturer. { products { id price, manufacturer: { name } } } has invalid colon syntax.

4. Final Answer:

   { products { id price manufacturer { name } } } -> Option B

5. Quick Check:

   Select only needed nested fields [OK]

Hint: Nest only needed fields inside parent fields [OK]

Common Mistakes:

• Selecting unwanted nested fields
• Placing nested fields outside their parent
• Using colon instead of braces for nesting