Django webapp - tracking financial account information - django

Question

I need some coding advice as I am worried that I am creating, well, bloated code that is inefficient.
I have a webapp that keeps track of a company's financial data. I have a table called Accounts with a collection of records corresponding to the typical financial accounts such as revenue, cash, accounts payable, accounts receivable, and so on. These records are simply name holders to be pointed at as foreign keys.
I also have a table called Account_Transaction which records all the transactions of money in and out of all the accounts in Accounts. Essentially, the Account_Transaction table does all the heavy lifting while pointing to the various accounts being altered.
For example, when a sale is made, two records are created in the Account_Transaction table. One record to increase the cash balance and a second record to increase the revenue balance.
Trans Record 1:
Acct: Cash
Amt: 50.00
Date: Nov 1, 2011
Trans Record 2:
Acct: Revenue
Amt: 50.00
Date: Nov 1, 2011
So now I have two records, but they each point to a different account. Now if I want to view my cash balance, I have to look at each Account_Transaction record and check if the record deals with Cash. If so, add/subtract the amount of that record and move to the next.
During a typical business day, there may be upwards of 200-300 transactions like the one above. As such, the Account_Transaction table will grow pretty quickly. After a few months, the table could have a few thousand records. Granted this isn't much for a database, however, every time the user wants to know the current balance of, say, accounts receivable, I have to traverse the entire Account_Transaction table to sum up all records that deal with the account name "Accounts Receivable".
I'm not sure I have designed this in the most optimal manner. I had considered creating a distinct table for each account (one for "Cash", another for "Accounts Receivable" another for "Revenue" etc...), but with that approach I was creating 15-20 tables with the exact same parameters, other than their name. This seemed like poor design so I went with this Account_Transaction idea.
Does this seem like an appropriate way to handle this kind of data? Is there a better way to do this that I should really be adopting?
Thanks!

Answer 1

Why do you need to iterate through all the records to figure out the status of Accounts Receievable accounts? Am I missing something in thinking you can't just use a .filter within the Django ORM to selectively pick the records you need?
As your records grow, you could add some date filtering to your reports. In most cases, your accountant will only want numbers for this quarter, month, etc., not entire historic data.
Add an index to that column to optimize selection and then check out Djangos aggregation to Sum up values from your database.
Finally, you could do some conservative caching to speed up things for "quick view" style reports where you just want a total number very quickly, but you need to be careful with this to not have false positives, so reseting that cache on any change to the records would be a must.

Answer 2

Why don't you keep track of the exact available amount in the Account table? The Account_Transaction could only be used to view transaction history.