In addition to the DB datastore exceptions class, the NDB datastore provides the following exception classes:

exception ComputedPropertyError()
:   Raised when attempting to set a value to or delete a computed property.

exception InvalidPropertyError()
:   Raised when a property is not applicable to a given use. For example, a property must exist and be indexed to be used in a query's projection or group by clause.

exception ReadonlyPropertyError()
:   Raised when attempting to set a property value that is read-only.

exception UnprojectedPropertyError()
:   Raised when getting a property value that's not in the projection.