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graphaware / neo4j-uuid

GraphAware Runtime Module that assigns a UUID to all nodes (and relationships) in the graph transparently
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UUID Assignment on Post Save #20

Closed jarellm closed 8 years ago

jarellm commented 8 years ago

Currently UUID assignment happens in the before commit phase.

Are there any plans to support Event.TYPE.POST_SAVE as mentioned here

http://graphaware.com/neo4j/2016/04/13/neo4j-ogm-events-part-1.html

such that the plugin behaves like JPA's IdGenerator and Oracle's sequence?

ikwattro commented 8 years ago

Hi,

The reason why it's done in beforeCommit is that in afterCommit the transaction has been commited so no changes can be done in the database anymore.

Note that as Cypher would already have compiled the result to the user, it is impossible for the plugin to return the uuid property as part of the result, so I'm afraid it can't be used as like you want without an extra statement sent to the database.

You would better use an application side uuid generator, like eaio uuid and add the uuid on the node property in the before save event like explained in the article you mentioned.

NB: Technically it is possible to use the plugin if OGM would support it as an ID Generation Strategy, meaning that during the commit, the OGM would now if this plugin is used and perform an extra statement to retrieve the uuid properties of the given node ids, this would involve a LOT of changes but can be a nice idea of extensibility points of the OGM, I'll discuss this with the team for the long term plan of the OGM.

jarellm commented 8 years ago

Thanks for the clarification Cristophe. I understand it can't be done in afterCommit, and like you said, requires changes in Neo4J itself to support such behavior. It just makes me wonder why Neo4j has limited itself to beforeCommit and afterCommit transaction listeners.