Value & revision for a transaction entry

[grossvater]

Hi,
I loop over transactions with transaction reader (for an embedded store):

rtx := st.NewTxHolder()
r, err := st.NewTxReader(1, false, rtx)

for {
    txi, err := r.Read()
    for _, e := range txi.Entries() {
        key := e.Key()
        // value := ??
        // revision := ??
    }
}

How could I get the revision and value set by the transaction?
Thanks.

[jeroiraz]

When iterating over raw transactions, entries do not hold the actual payload but a reference to the value (and its digest). The store provides the ReadValue method to fetch the actual value:

value, err := st.ReadValue(e)

[grossvater]

Great! What about the revision? I would have expected to be part of the entry.

[jeroiraz]

revision is not part of the raw transaction data, at least not in current implementation. The reason for this is that keeping track of the revision requires the indexing to be fully synchronized or some other data structure, which may not be as fast as the commit log.

revision of an entry requires reading the value by its associated key st.Get(key)

[grossvater]

I understand. But still, if need the revision of key, created by a specific transaction, how could I get it? I saw

History(key []byte, offset uint64, descOrder bool, limit int) (txs []uint64, hCount uint64, err error)

so taking the index of the transaction from txs is the way?

[jeroiraz]

hCount gives the total number of revisions (or key updates).
If desOrder is true:

• the txs[0] is the latest update, so revision would match hCount
• then revision would be hCount - txIndex
  If not descending order:
• then the first update is at txs[0]
• then revision would be 1 + txIndex

Feel free to open a feature request on how to get the revision for a key at a specific tx

[grossvater]

Ok, thanks for all the information.