List types in GraphQL - Step-by-Step Execution

Concept Flow - List types

Define List Type

↓

Use square brackets [

↓

Specify element type inside brackets

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Apply list type in schema

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Query returns array of elements

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Access elements by index or iterate

List types in GraphQL are defined by wrapping a type in square brackets to represent an array of that type.

Execution Sample

GraphQL

type Query {
  books: [String]
}

query {
  books
}

Defines a query returning a list of strings, then queries that list.

Execution Table

Step	Action	Type/Value	Result/Output
1	Define 'books' field type	[String]	Field 'books' expects a list of strings
2	Write query to fetch 'books'	query { books }	Request list of strings
3	Server resolves 'books'	["Book A", "Book B", "Book C"]	Returns array of strings
4	Client receives response	{ "books": ["Book A", "Book B", "Book C"] }	Data is a list of strings
5	Access first element	books[0]	"Book A" - Access element by index
6	Iterate over list	for each book in books	"Book A", "Book B", "Book C" - Process each element
7	End	-	Query complete, list data handled

💡 Query completes after returning the list of strings.

Variable Tracker

Variable	Start	After 3	After 4	After 5	Final
books	undefined	["Book A", "Book B", "Book C"]	["Book A", "Book B", "Book C"]	"Book A"	["Book A", "Book B", "Book C"]

Key Moments - 3 Insights

Why do we use square brackets [] in GraphQL type definitions?

Square brackets indicate a list type, meaning the field returns multiple items of the specified type, as shown in execution_table step 1.

Is the list returned by a GraphQL query always ordered?

Yes, the list preserves order, so accessing by index like books[0] returns the first element, as seen in step 5.

Can the list contain null values or be empty?

Yes, lists can be empty or contain nulls unless specified otherwise with non-null modifiers, but this example shows a full list in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what type is the 'books' field defined as in step 1?

A [Int]

B String

C [String]

D Int

💡 Hint

Check the 'Type/Value' column in step 1 of the execution_table.

At which step does the client receive the list of books?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look for when the response data is shown in the execution_table.

If the 'books' list was empty, which step's output would change?

A Step 3

B Step 5

C Step 6

D Step 4

💡 Hint

Step 3 shows the server's resolved list value.

Concept Snapshot

List types in GraphQL use square brackets [] around a type.
They represent arrays of that type.
Example: [String] means a list of strings.
Queries return lists as arrays.
Access elements by index or iterate.
Lists preserve order and can be empty.

Full Transcript

In GraphQL, list types are defined by wrapping a type in square brackets, like [String], to indicate a list of that type. When a query requests a field with a list type, the server returns an array of those elements. The client receives this list and can access elements by index or iterate over them. Lists preserve the order of elements and can be empty or contain nulls unless specified otherwise. This visual trace showed defining a list type, querying it, receiving the list, and accessing elements step-by-step.