Select For Update Transaction using Sequelize Sample

querytest.js

const Sequelize = require('sequelize');
const sequelize = new Sequelize('database', 'root', 'password', {
  host: 'localhost',
  dialect: 'mysql'
});

const Account = sequelize.define('account', {
  balance: {
    type: Sequelize.INTEGER,
    allowNull: false,
    defaultValue: 0
  }
});

async function updateBalance(accountId, amount) {
  const transaction = await sequelize.transaction();

  try {
    // Lock the account row for update
    const account = await Account.findOne({
      where: { id: accountId },
      lock: transaction.LOCK.UPDATE,
      transaction
    });
    console.log('Account balance before update:', account.balance);

    await new Promise(resolve => setTimeout(resolve, 2000));

    // Update the balance
    account.balance += amount;

    // Save and commit
    await account.save({ transaction });
    await transaction.commit();

  } catch (error) {
    await transaction.rollback();
    throw error;
  }
}

// Usage
(async () => {
  await sequelize.sync({ force: true });
  await Account.create({ balance: 100 });

  // Transaction 1
  updateBalance(1, -100).then(() => {
    console.log('Transaction 1 completed');
  }).catch(console.error);

  // Transaction 2
  updateBalance(1, 100).then(() => {
    console.log('Transaction 2 completed');
  }).catch(console.error);
})();