Document metadata as struct fields

Firestore provides additional fields for each document:

• _firestore_id: the document ID, whether the client chose it or Firestore generated it;
• _firestore_full_id: the full document name, such as projects/my-project/databases/(default)/documents/my-collection/my-id;
• _firestore_created: the time at which the document was created;
• _firestore_updated: the time at which the document was last changed.

A stored document carries its name in Core and pipeline results. A Core aggregation result, and the result of a pipeline stage that builds new documents, such as .fields() or .aggregate(), has no document name, and so neither _firestore_id nor _firestore_full_id. A SQL row has no name unless the statement selects __name__. Make a field that reads either of them an Option, see Query and write semantics.

To be able to read them the library makes them available as system fields for the Serde deserializer with reserved names, so you can specify them in your structures as:

use firestore::*;
use serde::{Deserialize, Serialize};
#[derive(Debug, Clone, Deserialize, Serialize)]
struct MyTestStructure {
    #[serde(alias = "_firestore_id")]
    id: Option<String>,
    #[serde(alias = "_firestore_created")]
    created_at: Option<FirestoreTimestamp>,
    #[serde(alias = "_firestore_updated")]
    updated_at: Option<FirestoreTimestamp>,
    some_string: String,
    one_more_string: String,
    some_num: u64,
}

Complete example available here.