Scan deletedAt (time or null) in findConfigs, findRulesConfigs and GetConfig

[lelenanam]

Add deleted_at to GetConfig, findConfigs and findRulesConfigs functions so they can return actual value of deleted_at for later use in ruler. Otherwise, ruler never discoveries deleted configs and never delete them from the map.

By default deleted_at column in DB set to NULL so we scan this into pq.NullTime variable (because we cannot store nil value into type time.Time).
To restore config we set deleted_at column in DB to NULL.

fixes https://github.com/weaveworks/service-conf/issues/1859

[bboreham]

Please give more explanation of the issue - this is a public repo so you can't just link to a private one.
And there isn't any information in that issue anyway about what really went wrong.

[bboreham]

I don't understand this. Why can't the zero time stand for "null" ?

[lelenanam]

We cannot store nil time into time.Time variable.
Added description of the PR.

[bboreham]

The zero value is time.Time{}, and can be checked like DeletedAt.IsZero()

[lelenanam]

Yes, zero time can stand for null, but opposite doesn't work: null cannot stand for zero time when I scan values from DB:
panic: sql: Scan error on column index 2: unsupported Scan, storing driver.Value type <nil> into type *time.Time

[bboreham]

Fine; use a DB-related type in the DB code but don't export it into the rest of the code.

[lelenanam]

We can use another variable to scan but I think it will complicate code.

[bboreham]

Putting an unfamiliar type in this struct is a huge overhead to understanding. Adding an extra variable in the scan code, which already has several variables for scanning only, is easy to understand.

[lelenanam]

Fixed, PTAL

[lelenanam]

This cfg.DeletedAt has to be time or null to be able to store null time from DB.

[lelenanam]

This cfg.DeletedAt has to be time or null to be able to store null time from DB.