How do you deal with multiple currencies and exchange rates in your database and logic layer?

2 Use decimal or integer types

Another important decision is how to store monetary values in your database. You should avoid using floating-point types, such as float or double, as they can introduce rounding errors and imprecision due to their binary representation. Instead, you should use decimal or integer types, such as decimal or bigint, as they can store exact decimal values. If you use decimal types, you should specify the precision and scale of the values, such as decimal(18,4), which means 18 digits in total and 4 digits after the decimal point. If you use integer types, you should store the values in the smallest unit of the currency, such as cents or pennies, and multiply or divide by 100 when displaying or converting them.

3 Use a reliable source of exchange rates

To convert between different currencies, you need to use a reliable source of exchange rates that provides accurate and up-to-date data. You can use various APIs or services that offer currency conversion, such as Fixer, Open Exchange Rates, or Currency Layer. You should also consider the frequency and timing of the exchange rate updates, as they can affect the accuracy and consistency of your conversions. For example, if you use daily exchange rates, you should use the same rate for the whole day, regardless of when the transaction occurs. Alternatively, you can use real-time or historical exchange rates, depending on the nature and purpose of the transaction.

4 Store the original and converted values

When you convert a monetary value from one currency to another, you should store both the original and the converted values in your database. This way, you can preserve the integrity and traceability of the transaction, and avoid losing information or introducing errors due to repeated conversions. For example, if a customer pays $100 USD for a product that costs €80 EUR, you should store both the $100 USD and the €80 EUR values in your database, along with the exchange rate used for the conversion. This will allow you to display the correct amounts to the customer and the seller, and to generate accurate reports and invoices.

6 Test and validate your conversions

Finally, you should test and validate your currency conversions in your logic layer, to ensure that they work correctly and consistently. You should use unit tests and integration tests to verify that your conversions are accurate, reliable, and secure. You should also use mock data or stubs to simulate different scenarios and edge cases, such as invalid or missing exchange rates, currency fluctuations, or rounding errors. You should also monitor and audit your conversions, to detect and resolve any issues or anomalies that might occur in production.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?