If you dont want to store the data and want them on demand you can use an alternative call (i.e. https://data.fixer.io/api/latest?access_key='+APIKEY+’&base=’+FROMCURRENCY+’&symbols=’+TOCURRENCY)
EX
You should use the currency exchange module from Marketplace.
According to their Documentation you can sync the Exchange rates for almost all Currency types and bring it into your Domain Model.
Then based on your needs you can draw a relationship from your Domain model entity to theirs (Marketplace module Domain Model Entity) and use it.