Hey everyone! I'm a frontend developer excited to create a finance management app for personal use. However, I'm a little unsure about the best approach to calculate account balances due to my limited experience with databases and backend setups.
I'm considering two options:
1. Using a database trigger to update the balance every time a new transaction is inserted. But what if I need to edit an existing transaction later?
2. Creating an additional table to store account balances, which would be updated periodically.
With option 1, I'm worried about tracking historical balances efficiently. I'd love to hear your thoughts on this!
1 Answer
When managing account balances in your app, it's best to treat transactions as an immutable record. Instead of storing a balance directly with the account, calculate it dynamically by summing all transactions whenever you need it. This method is reliable and prevents data issues caused by race conditions. It also makes it easy to track balances at any given point in time.
If you want to edit or delete a transaction, do it by creating a new compensating transaction, rather than modifying the original record. This way, you keep a complete history of your finances. Here’s a simplified way to set up your database tables and queries:
```sql
CREATE TABLE accounts (
id SERIAL PRIMARY KEY,
name VARCHAR(255) NOT NULL,
account_type VARCHAR(50) NOT NULL,
currency VARCHAR(3) NOT NULL,
initial_balance DECIMAL(15, 2) NOT NULL DEFAULT 0.00
);
CREATE TABLE transactions (
id SERIAL PRIMARY KEY,
account_id INTEGER NOT NULL REFERENCES accounts(id),
transaction_date DATE NOT NULL,
amount DECIMAL(15, 2) NOT NULL,
is_deleted BOOLEAN NOT NULL DEFAULT FALSE
);
-- Query for Current Balance
SELECT
a.initial_balance + COALESCE(SUM(t.amount), 0) AS current_balance
FROM
accounts a
LEFT JOIN
transactions t ON a.id = t.account_id AND t.is_deleted = FALSE
WHERE
a.id = [your_account_id]
GROUP BY
a.initial_balance;
```
This ensures you can always access your current and historical balances without duplicating data or running into performance issues.
How do I distinguish between actual transactions and compensating ones when displaying them? I get that calculating the balance on the fly works for personal use, but won't that slow down the app if there are billions of transactions?
I implemented a similar system and am on the lookout for performance hiccups once transaction numbers climb. My plan is to do annual account settlements to simplify balances. I’m still figuring out the best way to implement this.