Building Google Cloud Platform Solutions

Ancestry paths and keys

While Datastore does not support the arbitrary relations between data seen in an RDBMS, it does support a hierarchical structuring of relationships in the form of ancestors and descendants. Every entity has zero or one ancestors, and zero or more descendants. Ancestry provides a neat way to organize relational data.

As we'll see, this structuring of data is significant in several aspects of Datastore, including queries, consistency, and transaction performance. An entity's ancestors must be declared at the time of an entity's creation, and can never be removed unless that entity is deleted.

Each entity in Datastore has a globally unique key, which is used when referencing the entity in operations such as lookups and ...