Placeholder: MySQL fractional seconds in time/datetime

[paul-rouse]

This is just a placeholder arising from the recent discussions about the test failures caused by MySQL changing its handling of fractional seconds in date/time types (#702 (comment), #693 (comment)).

The idea is that persistent-mysql might move towards using SQL types like datetime(6), now that MySQL itself supports types with fractional seconds (since 5.6.4). Almost certainly an explicit option will be needed to enable this, and possibly a runtime test as well: the behaviour would be changed on those MySQL versions which do support it, and older versions of MySQL, which don't, are still in use (eg "trusty").

It is also an option to do nothing. The documentation could be improved to explain the default behaviour and how it can be modified by using sqltype=....

This issue is here while I am thinking about the options, and to invite comments!

[paul-rouse]

I am tending towards the "do nothing" approach, together with a documentation improvement. I think it may be better for the developer to be explicit about the storage types when faced with interrelated considerations including: changing existing application behaviour, migrating existing databases, and whether the application will always run against a MySQL server version which supports fractional seconds.

The downside is that any use of sqltype makes a persistent model less portable between different backends. It is not obvious to me that people will use fractional seconds often enough for this to matter much. However, I think the question is still open...

[psibi]

It would be nice if you can link this issue on the changelog. Sorry for saying it late.

[paul-rouse]

Good point! I'll push an edit

[paul-rouse]

Closing as there have been no comments for a month. I have put a note in the documentation (#721).