[DDC-3107][Persister] Remove the insertSql cache

[tyx]

Here is a piece of code which leads to an exception if we keep it :
https://gist.github.com/tyx/353de6d6aaf367abd6e6

Sure it is an edge case with tricks but I'm sure Doctrine does not need this kind of optimization.

My 2 cent

[doctrinebot]

Hello,

thank you for creating this pull request. I have automatically opened an issue
on our Jira Bug Tracker for you. See the issue link:

http://www.doctrine-project.org/jira/browse/DDC-3107

We use Jira to track the state of pull requests and the versions they got
included in.

[Ocramius]

@tyx can you convert that example into a unit test? We can't really remove the insert sql cache, as it would impact performance quite a bit. Instead, we can see if we can instantiate a new persister per row (depending on the use case)

[tyx]

Yes you're right. I will do that.

I spent quite a lot of time to find the origin of this problem so I admit my solution could look radical ;)

[guilhermeblanco]

Modifying ID Generation at runtime is weird and source of errors. You just hit one of them.

-1 on this change.