When mapping a one-to-one association using @PrimaryKeyJoinColumn, it may be beneficial to establish a relationship in Neo4j in order to save a node look-up and benefit from node navigation instead. That'd require some changes on the engine side, as the dialect is only invoked for the two duple operations (for each side of the association), but without any association meta-data.

From IRC:

gmorling we don't materialize the reference as FK in RDMBS either, so why do you think it should be done for neo4j? 13:13
emmanuel because in RDBMS, you can do joins freely. In k/v or documents you embed the data or not and if you don't you are a lookup away. But in Neo4J a lookup is the more expensive operation compared to a node jump 13:14
emmanuel and I don't know if you can express Cypher queries on /implicit/ associations 13:15
gmorling but if you want a relationship, why would you go for this sort of mapping than? 13:15
emmanuel because it's conceptually beautiful 13:15
gmorling lol 13:15
emmanuel true if you write a neo4j only app, you would not 13:15
emmanuel but for a multi abckend app you might