Allow to use ImpermanentGraphDatabase with EmbeddedDriver

The docs says “As you can see to use an impermanent data store, you just omit the URI attribute.”

But this is not equivalent to ImpermanentGraphDatabase. ImpermanentGraphDatabase doesn’t create any temporary files and seems to be slightly faster (although I don’t have any benchmark for this at hand).

I can do following, which is slightly awkward, but seems to work fine.

Components.setDriver(new EmbeddedDriver(new TestGraphDatabaseFactory().newImpermanentDatabase()));​    
new SessionFactory(".. packages .."); // no configuration instance there

It also works with parallel execution, when each worker runs in its own JVM (I tested gradle’s maxParallelForks and expect maven’s forkCount would work as well).

[geld0r]

Without this, it is also not possible to pass any configuration to the embedded neo4j instance (e.g. via neo4j.conf with Neo4j 3.0). This is prohibits upgrades from Neo4j 2.x to 3.x as setting the

dbms.allow_format_migration=true

option is not possible.

See this StackOverflow. As a workaround, doing the migration externally is suggested. However this may not be possible in all scenarios.

[michael-simons]

See my comment here: https://github.com/neo4j/neo4j-ogm/issues/408#issuecomment-442465303.