Spring Data Neo4j - Neo4j in Action - page 224

(modeled by the referredBy property ) is an excellent example of this. Note that
this property must be a reference to another node entity.
Basic relationships to zero or more other node entities are modeled with a Set , List ,
Collection ,or Iterable class,withthereferencednodeentityasthecollectiontype.
The use of a Set , List , or Collection class signifies that the field is modifiable from
the containing node's perspective; an Iterable class indicates this should be treated
as read-only. Based on the contained node entity class type and its annotations, SDN
will be able to work out that your intention is for this field to represent a basic relation-
ship. If, however, you'd like to overwrite any of the defaults inferred, you can add an
@RelatedTo annotation. The friends relationships between users is an example.
Note how in this case we added the @RelatedTo annotation with the type property to
specify the underlying Neo4j relationship type as IS_FRIEND_OF rather than the default
value that SDN would have inferred if it were not there. In the absence of the annotation,
SDN would have used the name of the field, friends , as the name to be used for the un-
derlying relationship type property.
Rich relationships, those represented by an underlying Neo4j relationship with associated
properties, are also modeled with the same Collection class as basic relationships. In
this case, however, the type of the contained entity in the collection is a relationship entity
rather than a node entity. To recap, a relationship entity represents the underlying Neo4j
relationship along with any associated properties that were also modeled in the entity (see
section 9.2.4 ) .Thisprovidesaneatwaytoaccesstherichinformationontherelationshipit-
self,whilestillbeingabletogettotheentityorentitiesontheotherend.Aswithbasicrela-
tionships, without any annotations, SDN can work out that you're creating such references
based solely on the fact that the type of class contained in the collection has been defined
as a relationship entity.Again, if youwish to override any ofthese relationship defaults as-
sumed by SDN, you can apply the @RelatedToVia annotation. As you've already seen,
the views fieldreference representingtherelationshipbetweena User anda Movie
is a good example; the additional stars rating serves to enhance the information about
the relationship between these two entities. Notice the different Collection class used
for the views property in the case of the User and Movie nodes, namely Set<View-
ing> and Iterable<Viewing> .Thismeansthatthe views propertycanbemodified
from the User node perspective but not from the Movie node. Conceptually, users rate
movies; movies don't apply ratings to users.