[RFC] "Nested" calls to DocumentManager::flush()

[alcaeus]

Hello all,

currently it is possible to flush() the DocumentManager multiple times while it is already flushing. One example is a lifecycle event subscriber that calls some method that inserts another document and flushes the DocumentManager.
Currently, this case is not handled, the DocumentManager will happily run the nested flush() operation which can cause a bunch of issues. My suggestion is that the DocumentManager prevents such calls, unless such functionality breaks existing behavior. Comments?

[gruberro]

I'd like to see this change, as this would prevent me from a lot of trouble 👍

[malarzm]

I remember using this to flush single document during bigger flush and nothing bad happened to me in the meantime

[alcaeus]

Let's say there is an event subscriber that listens to the onFlush event. That subscriber loops all changesets and does something if a specific field has changed. You've also got a second subscriber that listens to the postPersist event. That one creates a new document to be inserted and calls flush($document). This will cause the onFlush handler to be called a second time, and it will actually re-do whatever it has done for the first document since the document is still in the changesets (it will only be removed from there after the postFlush event has been triggered.
I can try to gist a use case that provokes this if you want.

[malarzm]

I'm not saying it can't break, just throwing my 2 cents saying that I'm currently using flush within a flush :)

[alcaeus]

Ah, sorry :)
Yeah, I was thinking about how it could be made optional or whether the flushes could be correctly isolated. Technically, if the second flush tracked its own set of changes, it would be no problem.

[alcaeus]

Long time no see - just referencing the comments over in the ORM repository:

Calling flush() inside a lifecycle listener is indeed not allowed.

(Source

Given that, I'd try to come up with a solution for 2.0 along with a deprecation notice for 1.2.

[malarzm]

#1722 prevents user from flushing more than once at a time