Bidirectional relationships in GraphQL - Step-by-Step Execution

Concept Flow - Bidirectional relationships

Define Type A

↓

Add field referencing Type B

↓

Define Type B

↓

Add field referencing Type A

↓

Query Type A -> Access Type B

↓

Query Type B -> Access Type A

Bidirectional relationships connect two types so each can access the other through fields.

Execution Sample

GraphQL

type Author {
  id: ID!
  name: String!
  books: [Book!]!
}

type Book {
  id: ID!
  title: String!
  author: Author!
}

Defines Author and Book types where Author has many Books and each Book has one Author.

Execution Table

Step	Action	Evaluation	Result
1	Define Author type with books field referencing Book list	Author.books is a list of Book	Author can access Books
2	Define Book type with author field referencing Author	Book.author is a single Author	Book can access Author
3	Query Author with books field	Fetch Author and their Books	Returns Author data with list of Books
4	Query Book with author field	Fetch Book and its Author	Returns Book data with Author info
5	Access Author from Book.author	Navigate from Book to Author	Author details retrieved
6	Access Books from Author.books	Navigate from Author to Books	List of Books retrieved
7	End of execution	All bidirectional links verified	Execution complete

💡 All bidirectional references established and queries return expected linked data

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
Author.books	undefined	list of Book references	unchanged	unchanged	list of Book references
Book.author	undefined	undefined	Author reference assigned	unchanged	Author reference assigned

Key Moments - 2 Insights

Why do we need to define fields on both types for bidirectional relationships?

Because each type needs a field to access the other, as shown in execution_table rows 1 and 2 where Author.books and Book.author are defined separately.

Can we query one side and get data from the other automatically?

Yes, once both sides are linked, querying Author.books or Book.author returns related data, as shown in rows 3 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the Book type linked back to Author?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Check the Action column for when Book.author is defined (Step 2).

According to variable_tracker, what is the value of Author.books after step 1?

A list of Book references

B Author reference

C undefined

D empty list

💡 Hint

Look at Author.books row and After 1 column in variable_tracker.

If we remove the author field from Book, what happens to the bidirectional relationship?

A Author can still access Books

B Book can no longer access Author

C Both sides lose access

D No effect on queries

💡 Hint

Refer to key_moments about needing fields on both types for bidirectional access.

Concept Snapshot

Bidirectional relationships connect two types with fields referencing each other.
Define a field on Type A pointing to Type B and vice versa.
This allows queries from either side to access related data.
Example: Author has books field (list of Book), Book has author field (single Author).
Both fields must be defined for full bidirectional access.

Full Transcript

Bidirectional relationships in GraphQL mean two types reference each other through fields. For example, an Author type has a books field that lists Book types, and each Book type has an author field pointing back to Author. This setup lets you query from Author to get their Books, or from Book to get its Author. The execution flow starts by defining Author with a books field, then Book with an author field. Queries then fetch linked data from either side. Variables track these references as they are assigned. Key points include needing fields on both types for full bidirectional access and that queries return linked data once both sides are connected. The visual quiz tests understanding of when links are defined and what happens if one side is missing.