Introduction

It's important to understand that on the Cardano blockchain, you don't directly interact with "smart contracts", at least not in the traditional sense.

Instead, you work with validators. These validators are responsible for verifying the actions taken in a given transaction, rather than executing or calling any actions themselves. Validators are pure functions that return true or false.

A validator checks whether the transaction meets its requirements, and if it does, the transaction is processed successfully. If the requirements are not met, the transaction fails (is not allowed to execute).

Concepts

const datum = Data.to(new Constr(0, [publicKeyHash]));

const DatumSchema = Data.Object({
  owner: Data.Bytes(),
});
type DatumType = Data.Static<typeof DatumSchema>;
const DatumType = DatumSchema as unknown as DatumType;

Workflow

const spend_val: SpendingValidator = {
  type: "PlutusV3",
  script: "59099a590997010000...", // CBOR format from plutus.json
};
 
const scriptAddress = lucid.utils.validatorToAddress(validator);

const tx = await lucid
  .newTx()
  .pay.ToContract(scriptAddress, { inline: datum }, { lovelace: 10_000_000n })
  .complete();

// Find the UTxO we want to spend
const allUTxOs = await lucid.utxosAt(scriptAddress);
const ownerUTxO = allUTxOs.find((utxo) => {
  if (utxo.datum) {
    const datum = Data.from(utxo.datum, DatumType);
    return datum.owner === publicKeyHash;
  }
});
 
// Spend script UTxO
const tx = await lucid
  .newTx()
  .collectFrom([ownerUTxO], redeemer) // Provide the redeemer argument
  .attach.SpendingValidator(spend_val) // Attach validator
  .complete();

Validator Types

Lucid Evolution supports different validator types, each serving a specific purpose:

// Attaching different validator types
.attach.SpendingValidator(validator)    // For spending UTxOs
.attach.MintingPolicy(validator)        // For minting tokens
.attach.CertificateValidator(validator) // For stake operations
.attach.WithdrawalValidator(validator)  // For reward withdrawals
.attach.VoteValidator(validator)        // For governance votes
.attach.ProposeValidator(validator)     // For governance proposals

Corresponding transaction operations:

.collectFrom(utxos, redeemer)           // Spending UTxOs
.mintAssets(assets, redeemer)           // Minting tokens
.delegateTo(stakeAddress, poolId, redeemer) // Stake delegation
.deRegisterStake(stakeAddress, redeemer)    // Stake deregistration
.withdraw(stakeAddress, rewardAmount, redeemer) // Reward withdrawal

Troubleshooting & Best Practices