CommandSimulator

The CommandSimulator is used during the publishing process, for partial publishing and workspace rebasing.

For this case, we want to apply commands including their constraint checks step by step, to see whether this set of commands applies cleanly without errors, and which events would be created by them, but we do NOT want to commit the updated projections or events.

Internally, we do the following:

• Create a database transaction in the GraphProjection which we will roll back lateron (to dry-run projection updates) (via {\Neos\ContentRepository\Core\CommandHandler\CommandSimulator::run()}). - Create an InMemoryEventStore which buffers created events by command handlers.
• execute all commands via {\Neos\ContentRepository\Core\CommandHandler\CommandSimulator::handle()} - -> this will do all constraint checks based on the projection in the open transaction (so it sees previously modified projection state which is not committed)
• -> it will run the command handlers, buffer all emitted events in the InMemoryEventStore -> note to avoid full recursion the workspace command handler is not included in the bus
• -> update the GraphProjection, but WITHOUT committing the transaction {[\Neos\ContentRepository\Core\Projection\ContentGraph\ContentGraphProjectionInterface::inSimulation()}

This](../../../../Neos/ContentRepository/Core/Projection/ContentGraph/ContentGraphProjectionInterface.html) is quite performant because we do not need to fork a new content stream.