Does Fetching a Parent Collection in Firebase Firestore Return Its Entire Sub-Collection Tree?

 

No, when you read a document from a collection in Firestore, it does not automatically return the entire tree of nested collections and sub-collections. Firestore is designed to allow for flexible and scalable data structures, meaning each collection and document is independent in terms of read operations.

How Firestore Reads Work

1.Reading a Document:

• When you read a document, you only get the fields within that document. Any sub-collections under that document are not included in the read operation.

2.Reading a Collection:

• When you read a collection, you get a list of documents within that collection. Again, this does not include any nested sub-collections.

Example Scenario

Consider the following Firestore structure:

users (collection)

  |

  |-- userID (document)

       |

       |-- name: "John Doe"

       |-- age: 30

       |

       |-- orders (sub-collection)

            |

            |-- orderID (document)

                 |-- product: "Laptop"

                 |-- price: 1200

• Reading the users collection will return a list of user documents (userID in this case) with their fields (name, age), but it won’t include the orders sub-collection.

• Reading the userID document will return the fields of that document (name, age), but not the orders sub-collection.

• Reading the orders sub-collection will return the documents within the orders collection, but only when you explicitly query this sub-collection.

How to Read Sub-Collections

To read a sub-collection, you must explicitly query it. Here’s how you can do it in Flutter:

import 'package:cloud_firestore/cloud_firestore.dart';

Summary

• Reading a document or collection in Firestore does not include its sub-collections automatically.

• To access sub-collections, you need to perform separate queries explicitly targeting those sub-collections.

• This design helps in optimizing data retrieval, ensuring that you only fetch the data you need, thus improving performance and reducing costs associated with read operations.