Moolah Diaries – Tracking Account Balances

Moolah has two separate Vuex modules, transactions and accounts. That’s a fairly reasonably logical separation, but in the new Moolah, it’s not a complete separation. Moolah only ever loads a subset of transactions – typically the most recent transactions from the currently selected account.  As a result, accounts have their own current balance property because they can’t always calculate it off of their transactions.

That means that sometimes the transaction Vuex module needs to make changes to state owned by the account module which is a rather unpleasant breach of module separation. While we ensured transaction balances remained consistent inside each mutation, we can’t do that for account balances because Vuex (presumably deliberately) makes it impossible for a mutation to access or change state outside of the module itself. Instead, I’ve used a simple Vuex plugin that watches the balance on the most recent transaction and notifies the account module when it changes:

import {mutations as accountsMutations} from './accountsStore';
export default store => store.watch(
(state) => {
return state.transactions.transactions.length >  
                                 ? state.transactions.transactions[].balance 
                                 : undefined;
},
(newValue, oldValue) => {
if (store.getters[“accounts/selectedAccount”] !== undefined && 
           newValue !== undefined) {
store.commit(‘accounts/’ + accountsMutations.updateAccount, {
id: store.state.selectedAccountId, 
                patch: {balance: newValue}
});
}
});

Most of the complexity there is dealing with the case where we don’t yet have transaction or don’t have a selected account. This essentially makes the syncing between transaction balances and account balances a separate responsibility that belongs to this plugin.

The plugin doesn’t completely handle transfers between accounts. The balance for the account currently being edited updates correctly, but the balance for the account on the other side of the transfer doesn’t update. I’m not particularly happy with the solution, but at least for now the responsibility of reacting to transfer changes is in the transaction module’s actions. The action can easily calculate the effects of transaction changes on the balances of other accounts and use Vuex’s dispatch to send a notification over to the account module to perform the update. Mutations can’t dispatch events so it has to be the action that does it.

This leaves responsibility for updating the current account’s balance with the plugin and the responsibility for updating other account’s balances with the transaction module which is ugly. Perhaps the transaction module actions should be responsible for all account balances. Probably the right answer is to extract a separate class/function that the transaction module notifies at the end of each action with the state of the transaction before and after. Then that new class/function is responsible for updating account balances. Will need to prod the code a bit to see if that really can be done…