Annotation used to mark a POJO property to be automatically populated with the document's ID when
the POJO is created from a Cloud Firestore document (for example, via
Any of the following will throw a runtime exception:
- This annotation is applied to a property of a type other than String or
- This annotation is applied to a property that is not writable (for example, a Java Bean getter without a backing field).
- This annotation is applied to a property with a name that conflicts with a read document
field. For example, if a POJO has a field `firstName` annotated by
@DocumentId, and there is a property from the document named `firstName` as well, an exception is thrown when you try to read the document into the POJO via
When using a POJO to write to a document (via
set(Object) or @
set(DocumentReference, Object)), the property annotated by
@DocumentId is ignored, which allows writing
the POJO back to any document, even if it's not the origin of the POJO.