Exchange rate client for SQL Anywhere

Retrieve the exchange rate for a currency from inside a SQL Anywhere database

This example shows how to access a web service from a SQL Anywhere database to retrieve the exchange rate for a currency. It makes use of SQL Anywhere's web client feature.

You'll find just one SQL file with all statements to create the needed database objects. These are:

• one table exchange_rate to store the exchange rate for a given date
• one web client function webclient_get_exchange_rate to access the web service
• one procedure fetch_exchange_rate; it calls the web client function, parses the JSON response and insert or updates the exchange rate in the table
• one event definition ExchangeRateFetcher that runs once a day and takes care for the whole process

Constraints

I'll use the exchange rate API from currencylayer. You have to register with this service and get your API key.

This example fetches the exchange rate for the Swiss franc in USD (symbol: CHF).

Both values, API key and currency symbol, can be edited in the procedure fetch_exchange_rate.

In a real use case you will likely want to store those values in a configuration table.

Installation

1. Create a new database (using dbinit) or reuse an existing one
2. Connect with iSQL to the database
3. Execute the script exchangerateclient.sql
4. Edit API key and currency symbol in the procedure fetch_exchange_rate

Use

• call procedure fetch_exchange_rate manually in iSQL and check the new record in table exchange_rate
• enable the event ExchangeRateFetcher - it will run daily at 14:00 (2pm)
• optionally change the schedule for that event

API response from currencylayer

If the API call to the currencylayer service was ok and you had a valid API key the response looks like this:

{
    "success": true,
    "terms": "https://currencylayer.com/terms",
    "privacy": "https://currencylayer.com/privacy",
    "timestamp": 1555653247,
    "source": "USD",
    "quotes": {
        "USDCHF": 1.014845
    }
}

Otherwise you'll get:

{
    "success": false,
    "error": {
        "code": 101,
        "type": "invalid_access_key",
        "info": "You have not supplied a valid API Access Key. [Technical Support: [email protected]]"
    }
}