CollectionReference A CollectionReference can be used for adding documents, getting document references, and querying for documents (using the methods inherited from Query).
 DocumentChange A DocumentChange represents a change to the documents matching a query.
 DocumentReference A DocumentReference refers to a document location in a Firestore database and can be used to write, read, or listen to the location.
 DocumentSnapshot A DocumentSnapshot contains data read from a document in your Firestore database.
 FieldValue Sentinel values that can be used when writing document fields with write() or updateData().
 Firestore Represents a Firestore Database and is the entry point for all Firestore operations
 FirestoreSettings Settings used to configure a FirebaseFirestore instance.
 Query A Query which you can read or listen to.
 QuerySnapshot A QuerySnapshot contains the results of a query.
 SetOptions An options object that configures the behavior of write() calls.
 SnapshotMetadata Metadata about a snapshot, describing the state of the snapshot.
 Source Configures the behavior of read() calls on CollectionReference, DocumentReference and Query.
 Transaction A Transaction is passed to a native detached thread to provide the methods to read and write data within the transaction context.
 WriteBatch A write batch, used to perform multiple writes as a single atomic unit.