Txn.SetEntryWithDiscard

[chernomyrdin]

First of all,
great system: simple design and enable endless possibilities!

I would like to propose the addition of SetEntryWithDiscard for Txn. Or somethig else fo set meta bit bitDiscardEarlierVersions in Entry.
For the same reason, a WriteBatch.SetEntryWithDiscard is also helpful, but to a lesser extent. I guess that would be very straightforward to implement.

Thanks again!

[ashish-goswami]

@chernomyrdin Thanks for raising the issue. We already have SetWithDiscard for Txn, which is similar to what you are proposing. However we don't have this in WriteBatch.
Feel free to raise a PR if possible.

[chernomyrdin]

I need save to database Entry with TTL and DiscadEarlierVersions at one time.
first variant code:

// SetEntryWithDiscard acts like SetEntry, but adds a marker to discard earlier
// versions of the key.
//
// The current transaction keeps a reference to the entry passed in argument.
// Users must not modify the entry until the end of the transaction.
func (txn *Txn) SetEntryWithDiscard(e *Entry) error {
	return txn.modify(&Entry{
		Key:       e.Key,
		Value:     e.Value,
		UserMeta:  e.UserMeta,
		ExpiresAt: e.ExpiresAt,
		meta:      bitDiscardEarlierVersions,
	})
}

or second variant:

// SetEntryWithDiscard acts like SetEntry, but adds a marker to discard earlier
// versions of the key.
//
// The current transaction keeps a reference to the entry passed in argument.
// Users must not modify the entry until the end of the transaction.
func (txn *Txn) SetEntryWithDiscard(e *Entry) error {
	e.meta = bitDiscardEarlierVersions
	return txn.modify(e)
}

What code style preferred?

[ashish-goswami]

@chernomyrdin ExpiredAt is exported field and hence can be set directly using dot operator like e.ExpiredAt = time.Now().Unix()

[ashish-goswami]

We have introduced new APIs for Entry. These APIs allows you to set more than one property on Entry. Finally calling SetEntry on Transaction/WriteBatch adds entry to Transaction/WriteBatch. #822