I currently have a utxo that i am getting like this.
initalMatchPool <- Map.filter (findInitalAmount fundAddress) <$> utxosAt scrAddress
How do i get the value of the datum attached to this specific utxo ?
Cardano Stack Exchange is a question and answer site for users and developers of the Cardano cryptocurrency ecosystem. It only takes a minute to sign up.Sign up to join this community
The ChainIndexTxOut type has a data field called
_ciTxOutValue :: Value and another that is
_ciTxOutDatum :: Either DatumHash Datum I'll show you how to get the value. Getting the datum is the same process with the extra step of having to extract it from the Either binding.
utxos <- utxosAt ... list = Map.toList utxos firstUtxo = head list ci = snd firstUtxo val = _ciTxOutVale ci
utxos is type Map(TxOutRef ChainIndexTxOut)
list is type [(TxOutRef, ChainIndexTxOut)]
firstUtxo is type (TxOutRef, ChainIndexTxOut)
ci is type ChainIndexTxOut
val is type Value
All those lines can be combined to
vals = _ciTxOutValue (snd (head (Map.toList utxos))) or if you want the sum of all the of the values instead of just the value in the first utxo at the address, you can do
vals = _ciTxOutValue <$> (snd <$> Map.toList utxos)
The upshot is that you might not find a datum but instead get a hash of the datum (it depends).
When submitting a transaction the full "unhashed" datum is not automatically attached to the output. This to save space and add usecased where the sender wants to keep the datum a secret. If it is not attached you will not find it onchain, only the hash of the datum used. Reversing this is (computational) impossible by construction.
In the other case, where is is attached you can retrieve it. As stated by Kyle Murphy the constructor
ChainIndexTxOut(1) that resulted from the filter "
findInitalAmount fundAddress" over all UTxO's sitting at the script address
scrAddress contains all info known of these outputs fitting the condition you specified.
utxosAt returns a map of two fields,
Map TxOutRef ChainIndexTxOut (2). Each
TxOutRef contains the hash of the transaction that made this utxo and an associated id relative to the other outputs of that transaction (
TxOutRef TxId Integer). Now the other field in the
Map is the
ChainIndexTxOut which can contain one of two things depending on the query. If you queried a script address this will be
Note That the
_ciTxOutDatum constructor holds a
Either DatumHash Datum. So if the UTxO contains a datum you can retrieve you can extract it with
Left like below
getDatum :: ChainIndexTxOut -> Maybe Datum getDatum o = case _ciTxOutDatum o of Left i -> Just i Right j -> Nothing
Hope this helps.
OffChain: It's a datum hash - so there is no reverse lookup if you don't know how to construct datums for a given contract. Datum values are usually provided by the consumer of a script UTxO.
If this is onchain code (which it does not look like), you can use a function called
findDatum to lookup datums provided by the consumer of a script UTxO.