Use two neo4j databases in single rails app

Question

I have two neo4j databases running on two different hosts. I connected my rails app to one of them while generating the app. Now I want to use other database as well with the app. How can I configure the app to connect to both the databases?

Answer 1

There’s not currently a good way to configure one Ruby process to use two sessions at the same time. If you are using Rails you can change the server by setting the NEO4J_URL environment variable. Otherwise you’d need to manage the session by setting Neo4j::ActiveBase.current_session or Neo4j::ActiveBase.on_establish_session (which will set the session for each new thread, which may be needed if you are running a multi-threaded process)

See: https://github.com/neo4jrb/neo4j/blob/master/lib/neo4j/active_base.rb

Answer 2

As Brian mentioned currently we cannot configure one Ruby process to use two sessions at the same time. We have to manage the session by setting Neo4j::ActiveBase.current_session (See: https://github.com/neo4jrb/neo4j/blob/master/lib/neo4j/active_base.rb)

The neo4j.yml sets the Neo4j::ActiveBase.current_session for you in the railtie. If you set Neo4j::ActiveBase.current_session after the app has started up it will override what was in the neo4j.yml. The current_session needs to be a Neo4j::Core::CypherSession object from the neo4j-core gem. (See the readme: https://github.com/neo4jrb/neo4j-core)

Also keep in mind, that currently neo4j does not support having different session for each model. So you might experience problem if, setting the session inside model. A better way would be to set session in the normal runtime of the app. You also might want to wrap the Neo4j::Core::CypherSession to get Query Proxy instead of Neo4j::Core objects. To this you have to specify wrap_level: :proc while declaring the adaptor. (Refer: https://github.com/neo4jrb/neo4j/blob/master/lib/neo4j/session_manager.rb#L14)

So in all, here is what you need to do

http_adaptor = Neo4j::Core::CypherSession::Adaptors::HTTP.new('http://neo4j:7474',{wrap_level: :proc}) Neo4j::ActiveBase.current_session = Neo4j::Core::CypherSession.new(http_adaptor)

this will establish a wrapped session with the desired database in 'http://neo4j:7474'