Starting development with Neo4j - Neo4j in Action - page 64

fromthe user nodeandbedirectedtothe movie node,thesameasthe IS_FRIEND_OF
relationship you used before.
Thereisonesignificantdifferencebetweenthe HAS_SEEN and IS_FRIEND_OF relation-
ships:the HAS_SEEN relationshipcontainstheadditionalinformationabouthowmuchthe
user liked the movie (represented by the number of stars the user gave to the movie). The
number of stars is therefore not a property of the user node (because a user can rate mul-
tiplemovies)orofthe movie node(themoviecanberatedbymultiple users),butrathera
property of the relationship between the user and the movie. You've seen how you can add
properties to nodes, but adding properties to relationships is a new concept at this point.
We mentioned before that Neo4j is a property graph. In Neo4j, property graph applies to
all graph entities—relationships as well as nodes. Adding a property to a relationship in
Neo4jisassimpleasaddingapropertytoanode.We'llguideyouthroughusingtheNeo4j
Core Java API to add properties to relationships.
Before we proceed, you need to add a new relationship type to the relationship enum.
The following snippet shows the updated MyRelationshipTypes enum with the new
HAS_SEEN relationship:
public enum MyRelationshipTypes implements RelationshipType{
IS_FRIEND_OF,
HAS_SEEN;
}
The next step is to create named relationships between nodes, which is achieved in the
same way that you added friendship relationships between users earlier in the chapter.
The API call for the creation of a relationship will return the Neo4j Relationship ob-
ject, and you can use it to add properties by calling the Relationship.set-Prop-
erty(String name, Object value) method.
The following listing shows the code that creates the HAS_SEEN relationships and adds
stars properties to them.