Firestore’s sub-collections and flat data models each have their own advantages. Sub-collections are ideal for complex hierarchical data structures, as they allow nested documents within a document. They also provide better query performance due to Firestore’s indexing system. However, they can increase complexity in code and may lead to higher costs due to multiple document reads.
On the other hand, a flat data model simplifies coding and reduces read operations, thus potentially lowering costs. But it might not be suitable for complex data structures and could result in slower queries if data size grows significantly.
The decision between these two should consider factors such as data structure complexity, expected database size, cost implications, and desired query performance.
