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Cross-Contract Hello Contract

The smart contract implements the simplest form of cross-contract calls: it calls the Hello NEAR example to get and set a greeting.

@call
query_greeting() {
  const call = near.promiseBatchCreate(this.hello_account);
  near.promiseBatchActionFunctionCall(call, "get_greeting", bytes(JSON.stringify({})), 0, 5 * TGAS);
  const then = near.promiseThen(call, near.currentAccountId(), "query_greeting_callback", bytes(JSON.stringify({})), 0, 5 * TGAS);
  return near.promiseReturn(then);
}

@call
query_greeting_callback() {
  assert(near.currentAccountId() === near.predecessorAccountId(), "This is a private method");
  const greeting = near.promiseResult(0) as String;
  return greeting.substring(1, greeting.length-1);
}

@call
change_greeting({ new_greeting }: { new_greeting: string }) {
  const call = near.promiseBatchCreate(this.hello_account);
  near.promiseBatchActionFunctionCall(call, "set_greeting", bytes(JSON.stringify({ greeting: new_greeting })), 0, 5 * TGAS);
  const then = near.promiseThen(call, near.currentAccountId(), "change_greeting_callback", bytes(JSON.stringify({})), 0, 5 * TGAS);
  return near.promiseReturn(then);
}

@call
change_greeting_callback() {
  assert(near.currentAccountId() === near.predecessorAccountId(), "This is a private method");

  if (near.promiseResultsCount() == BigInt(1)) {
    near.log("Promise was successful!")
    return true
  } else {
    near.log("Promise failed...")
    return false
  }
}

Quickstart

  1. Make sure you have installed node.js >= 16.
  2. Install the NEAR CLI

1. Build and Deploy the Contract

You can automatically compile and deploy the contract in the NEAR testnet by running:

npm run deploy

Once finished, check the neardev/dev-account file to find the address in which the contract was deployed:

cat ./neardev/dev-account  # dev-1659899566943-21539992274727

2. Get the Greeting

query_greeting performs a cross-contract call, calling the get_greeting() method from hello-nearverse.testnet.

Call methods can only be invoked using a NEAR account, since the account needs to pay GAS for the transaction.

# Use near-cli to ask the contract to query the greeting
near call <dev-account> query_greeting --accountId <dev-account>

3. Set a New Greeting

change_greeting performs a cross-contract call, calling the set_greeting({greeting:String}) method from hello-nearverse.testnet.

Call methods can only be invoked using a NEAR account, since the account needs to pay GAS for the transaction.

# Use near-cli to change the greeting
near call <dev-account> change_greeting '{"new_greeting":"XCC Hi"}' --accountId <dev-account>

Tip: If you would like to call change_greeting or query_greeting using your own account, first login into NEAR using:

# Use near-cli to login your NEAR account
near login

and then use the logged account to sign the transaction: --accountId <your-account>.