How to use Truffle Migrations to Modify the State of an Already Deployed Contract

Truffle makes it super easy to migrate new contracts.

One thing that was not clear to me was: how do I call methods on an already deployed contract?

It turns out it is actually quite easy. For example, to call a method that changes the state of an item on an existing contract would look something like:

const AwesomeContract = artifacts.require("./path/to/Awesome.sol");
require("dotenv-flow").config();

const awesomeContractAddress = process.env.AWESOME_CONTRACT_ADDRESS;

console.log(`awesomeContractAddress: [${awesomeContractAddress}]`);

module.exports = async deployer => {
  const awesomeContractInstance = await AwesomeContract.at(awesomeContractAddress);

  const someMethodTx = await awesomeContractInstance.someMethod(
    "FOO"
  );

  console.log("Events Fired During SomeMethof:");
  console.log("===========================\n");
  console.log(someMethodTx.logs);
 console.log("===========================\n");

In the above we can see that:

• We made a new migration .js file and put it in the migrations folder.
• We do not use the deployer: we are not deploying any new contract.
• We use AwesomeContract.at to refer to the contract's existing address.
• We store the transaction resulting from the contract method execution and console.log its logs so we can see what events were fired.
• Add/remove console.logs as you see fit, I did this for debuggability when this migration script runs.

I use dotenv-flow which is completely optional. This allows me to have .env files for different environments. For example, locally I have .env.local. dotenv-flow looks at the NODE_ENV environment variable to determine which .env file to use. To make it use my .env.local one I run truffle migrate as follows:

NODE_ENV=local truffle migrate