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Complex Cross Contract Call

This example presents 3 instances of complex cross-contract calls. Particularly, it shows:

  1. How to batch multiple function calls to a same contract.
  2. How to call multiple contracts in parallel, each returning a different type.
  3. Different ways of handling the responses in the callback.
Simple Cross-Contract Calls

Check the tutorial on how to use simple cross-contract calls

Obtaining the Cross Contract Call Example​

You have two options to start the Donation Example:

  1. You can use the app through Github Codespaces, which will open a web-based interactive environment.
  2. Clone the repository locally and use it from your computer.
CodespacesClone locally
Open in GitHub Codespaces🌐 https://github.com/near-examples/cross-contract-calls

Structure of the Example​

The smart contract is available in two flavors: Rust and JavaScript

┌── sandbox-ts # sandbox testing
│    ├── external-contracts
│    │    ├── counter.wasm
│    │    ├── guest-book.wasm
│    │    └── hello-near.wasm
│    └── main.ava.ts
├── src # contract's code
│    ├── internal
│    │    ├── batch_actions.ts
│    │    ├── constants.ts
│    │    ├── multiple_contracts.ts
│    │    ├── similar_contracts.ts
│    │    └── utils.ts
│    └── contract.ts
├── package.json
├── README.md
└── tsconfig.json

Smart Contract​

Batch Actions​

You can aggregate multiple actions directed towards one same contract into a batched transaction. Methods called this way are executed sequentially, with the added benefit that, if one fails then they all get reverted.

Getting the Last Response​

In this case, the callback has access to the value returned by the last action from the chain.

Calling Multiple Contracts​

A contract can call multiple other contracts. This creates multiple transactions that execute all in parallel. If one of them fails the rest ARE NOT REVERTED.

Getting All Responses​

In this case, the callback has access to an array of responses, which have either the value returned by each call, or an error message.

Multiple Calls - Same Result Type​

This example is a particular case of the previous one (Calling Multiple Contracts). It simply showcases a different way to check the results by directly accessing the promise_result array.

In this case, we call multiple contracts that will return the same type:

Getting All Responses​

In this case, the callback again has access to an array of responses, which we can iterate checking the results.

Testing the Contract​

The contract readily includes a set of unit and sandbox testing to validate its functionality. To execute the tests, run the following commands:

cd contract-advanced-ts
yarn
yarn test
tip

The integration tests use a sandbox to create NEAR users and simulate interactions with the contract.

Deploying the Contract to the NEAR network​

In order to deploy the contract you will need to create a NEAR account.

# Create a new account pre-funded by a faucet
near create-account <accountId> --useFaucet

Go into the directory containing the smart contract (cd contract-advanced-ts or cd contract-advanced-rs), build and deploy it:

cargo near build

cargo near deploy <accountId> with-init-call new json-args '{"hello_account":"hello.near-example.testnet","guestbook_account":"guestbook_account.near-example.testnet","counter_account":"counter_account.near-example.testnet"}' prepaid-gas '100.0 Tgas' attached-deposit '0 NEAR' network-config testnet sign-with-keychain send

CLI: Interacting with the Contract​

To interact with the contract through the console, you can use the following commands:

# Execute contracts sequentially
# Replace <accountId> with your account ID
near call <accountId> batch_actions --accountId <accountId> --gas 300000000000000   

# Execute contracts in parallel
# Replace <accountId> with your account ID
near call <accountId>  multiple_contracts --accountId <accountId> --gas 300000000000000   

# Execute multiple instances of the same contract in parallel
# Replace <accountId> with your account ID
near call <accountId> similar_contracts --accountId <accountId> --gas 300000000000000
info

If at some point you get an "Exceeded the prepaid gas" error, try to increase the gas amount used within the functions when calling other contracts

Versioning for this article

At the time of this writing, this example works with the following versions:

  • near-cli: 4.0.13
  • node: 18.19.1
  • rustc: 1.77.0
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