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Transfers & Actions

This page describes the different types of actions that a smart contract can perform on NEAR like transferring NEAR, calling other contracts, creating sub-accounts, and deploying contracts. It also explains how to add access keys to accounts.

Smart contracts can perform specific Actions such as transferring NEAR, or calling other contracts.

An important property of Actions is that they can be batched together when acting on the same contract. Batched actions act as a unit: they execute in the same receipt, and if any fails, then they all get reverted.

info

Actions can be batched only when they act on the same contract. You can batch calling two methods on a contract, but cannot call two methods on different contracts.

Transfer NEAR Ⓝ​

You can send $NEAR from your contract to any other account on the network. The Gas cost for transferring $NEAR is fixed and is based on the protocol's genesis config. Currently, it costs ~0.45 TGas.

  use near_sdk::{near, AccountId, Promise, NearToken};

  #[near(contract_state)]
  #[derive(Default)]
  pub struct Contract { }

  #[near]
  impl Contract {
    pub fn transfer(&self, to: AccountId, amount: NearToken){
      Promise::new(to).transfer(amount);
    }
  }
Why is there no callback?

The only case where a transfer will fail is if the receiver account does not exist.

caution

Remember that your balance is used to cover for the contract's storage. When sending money, make sure you always leave enough to cover for future storage needs.

Function Call​

Your smart contract can call methods in another contract. In the snippet below we call a method in a deployed Hello NEAR contract, and check if everything went right in the callback.

  use near_sdk::{near, env, log, Promise, Gas, PromiseError};
  use serde_json::json;

  #[near(contract_state)]
  #[derive(Default)]
  pub struct Contract { }

  const HELLO_NEAR: &str = "hello-nearverse.testnet";
  const NO_DEPOSIT: u128 = 0;
  const CALL_GAS: Gas = Gas(5_000_000_000_000);

  #[near]
  impl Contract {
    pub fn call_method(&self){
      let args = json!({ "message": "howdy".to_string() })
                .to_string().into_bytes().to_vec();

      Promise::new(HELLO_NEAR.parse().unwrap())
      .function_call("set_greeting".to_string(), args, NO_DEPOSIT, CALL_GAS)
      .then(
        Promise::new(env::current_account_id())
        .function_call("callback".to_string(), Vec::new(), NO_DEPOSIT, CALL_GAS)
      );
    }

    pub fn callback(&self, #[callback_result] result: Result<(), PromiseError>){
      if result.is_err(){
          log!("Something went wrong")
      }else{
          log!("Message changed")
      }
    }
  }
warning

The snippet showed above is a low level way of calling other methods. We recommend make calls to other contracts as explained in the Cross-contract Calls section.

Create a Sub Account​

Your contract can create direct sub accounts of itself, for example, user.near can create sub.user.near.

Accounts do NOT have control over their sub-accounts, since they have their own keys.

Sub-accounts are simply useful for organizing your accounts (e.g. dao.project.near, token.project.near).

  use near_sdk::{near, env, Promise, NearToken};

  #[near(contract_state)]
  #[derive(Default)]
  pub struct Contract { }

  const MIN_STORAGE: NearToken = NearToken::from_millinear(1); //0.001Ⓝ

  #[near]
  impl Contract {
    pub fn create(&mut self, prefix: String) {
      let account_id = prefix + "." + &env::current_account_id().to_string();
      Promise::new(account_id.parse().unwrap())
        .create_account()
        .transfer(MIN_STORAGE);
    }
  }
tip

Notice that in the snippet we are transferring some money to the new account for storage

caution

When you create an account from within a contract, it has no keys by default. If you don't explicitly add keys to it or deploy a contract on creation then it will be locked.

Creating .testnet / .near Accounts​

Accounts can only create immediate sub-accounts of themselves.

If your contract wants to create a .mainnet or .testnet account, then it needs to call the create_account method of near or testnet root contracts.

  use near_sdk::{near, Promise, Gas, NearToken };
  use serde_json::json;

  #[near(contract_state)]
  #[derive(Default)]
  pub struct Contract { }

  const CALL_GAS: Gas = Gas::from_gas(28_000_000_000_000);
  const MIN_STORAGE: NearToken = NearToken::from_yoctonear(1_820_000_000_000_000_000_000); //0.00182Ⓝ

  #[near]
  impl Contract {
    pub fn create_account(&mut self, account_id: String, public_key: String){
      let args = json!({
                  "new_account_id": account_id,
                  "new_public_key": public_key,
                }).to_string().into_bytes().to_vec();

      // Use "near" to create mainnet accounts
      Promise::new("testnet".parse().unwrap())
        .function_call("create_account".to_string(), args, MIN_STORAGE, CALL_GAS);
    }
  }

Deploy a Contract​

When creating an account you can also batch the action of deploying a contract to it. Note that for this, you will need to pre-load the byte-code you want to deploy in your contract.

  use near_sdk::{near, env, Promise, NearToken};

  #[near(contract_state)]
  #[derive(Default)]
  pub struct Contract { }

  const MIN_STORAGE: NearToken = NearToken::from_millinear(1100); //1.1Ⓝ
  const HELLO_CODE: &[u8] = include_bytes!("./hello.wasm");

  #[near]
  impl Contract {
    pub fn create_hello(&self, prefix: String){
      let account_id = prefix + "." + &env::current_account_id().to_string();
      Promise::new(account_id.parse().unwrap())
        .create_account()
        .transfer(MIN_STORAGE)
        .deploy_contract(HELLO_CODE.to_vec());
    }
  }
tip

If an account with a contract deployed does not have any access keys, this is known as a locked contract. When the account is locked, it cannot sign transactions therefore, actions can only be performed from within the contract code.

Add Keys​

When you use actions to create a new account, the created account does not have any access keys, meaning that it cannot sign transactions (e.g. to update its contract, delete itself, transfer money).

There are two options for adding keys to the account:

  1. add_access_key: adds a key that can only call specific methods on a specified contract.
  2. add_full_access_key: adds a key that has full access to the account.

  use near_sdk::{near, env, Promise, NearToken, PublicKey};

  #[near(serializers = [json, borsh])]
  #[derive(Default)]
  pub struct Contract { }

  const MIN_STORAGE: NearToken = NearToken::from_millinear(1100); //1.1Ⓝ
  const HELLO_CODE: &[u8] = include_bytes!("./hello.wasm");

  #[near]
  impl Contract {
    pub fn create_hello(&self, prefix: String, public_key: PublicKey){
      let account_id = prefix + "." + &env::current_account_id().to_string();
      Promise::new(account_id.parse().unwrap())
        .create_account()
        .transfer(MIN_STORAGE)
        .deploy_contract(HELLO_CODE.to_vec())
        .add_full_access_key(public_key);
    }
  }

Notice that what you actually add is a "public key". Whoever holds its private counterpart, i.e. the private-key, will be able to use the newly access key.

tip

If an account with a contract deployed does not have any access keys, this is known as a locked contract. When the account is locked, it cannot sign transactions therefore, actions can only be performed from within the contract code.

Delete Account​

There are two scenarios in which you can use the delete_account action:

  1. As the last action in a chain of batched actions.
  2. To make your smart contract delete its own account.
  use near_sdk::{near, env, Promise, NearToken, AccountId};

  #[near(contract_state)]
  #[derive(Default)]
  pub struct Contract { }

  const MIN_STORAGE: NearToken = NearToken::from_millinear(1); //0.001Ⓝ

  #[near]
  impl Contract {
    pub fn create_delete(&self, prefix: String, beneficiary: AccountId){
      let account_id = prefix + "." + &env::current_account_id().to_string();
      Promise::new(account_id.parse().unwrap())
        .create_account()
        .transfer(MIN_STORAGE)
        .delete_account(beneficiary);
    }

    pub fn self_delete(beneficiary: AccountId){
      Promise::new(env::current_account_id())
        .delete_account(beneficiary);
    }
  }
Token Loss

If the beneficiary account does not exist the funds will be dispersed among validators.

Token Loss

Do not use delete to try fund a new account. Since the account doesn't exist the tokens will be lost.