How to load data from Exchange Rates Api to Clickhouse

Before you start, ensure you have ClickHouse installed and running. You can download ClickHouse from the official website and follow the installation instructions for your operating system.

1. Install ClickHouse: Follow the installation instructions for your specific platform: https://clickhouse.com/docs/en/getting-started/install/
2. Start ClickHouse Server: Typically, after installation, you can start ClickHouse using service or systemctl commands, depending on your system.
3. Access ClickHouse Client: Use the ClickHouse client to connect to your ClickHouse server. You can usually do this by typing clickhouse-client in your terminal.
4. Create a Database: Once connected, create a new database for your exchange rate data:
   CREATE DATABASE exchange_rates;
5. Create a Table: Define a table schema that matches the data you will retrieve from the exchange rates API:
   USE exchange_rates;

CREATE TABLE rates (
date Date,
currency_code String,
rate Float64
) ENGINE = MergeTree()
PARTITION BY toYYYYMM(date)
ORDER BY (currency_code, date);

Write a script in a language of your choice (e.g., Python) to fetch data from the exchange rates API.

1. Choose a Programming Language: Python is a popular choice due to its simplicity and the availability of libraries for HTTP requests and data manipulation.
2. Write a Script to Fetch Data:

import requests
import datetime

# Replace with the actual API endpoint and your API key if necessary
url = "https://api.exchangeratesapi.io/latest"

# Make a GET request to the API
response = requests.get(url)
data = response.json()

# Extract the rates and base currency
base_currency = data['base']
rates = data['rates']
date = datetime.datetime.strptime(data['date'], '%Y-%m-%d').date()

# Prepare the data for insertion into ClickHouse
rows_to_insert = [(date, currency, rate) for currency, rate in rates.items()]

Continue the script to insert data into ClickHouse.

1. Install ClickHouse Driver: Install a ClickHouse driver for your chosen programming language. For Python, you can use clickhouse-driver:
   pip install clickhouse-driver
2. Connect to ClickHouse:
   from clickhouse_driver import Client

client = Client('localhost')
3. Insert Data into ClickHouse:
   # Insert data into the rates table
client.execute('INSERT INTO exchange_rates.rates (date, currency_code, rate) VALUES', rows_to_insert)

To keep your ClickHouse database updated, you can automate the data fetching and insertion process.

1. Schedule the Script: Use a scheduler like cron (on Unix-based systems) or Task Scheduler (on Windows) to run your script at regular intervals.
2. Error Handling: Enhance your script with error handling to manage potential issues with the API or database connections.
3. Logging: Implement logging to track the script’s execution history and any errors that occur.

Finally, test your entire setup to ensure it works as expected and monitor the system for any issues.

1. Test the Script: Run the script manually to verify that data is correctly fetched from the API and inserted into ClickHouse.
2. Monitor ClickHouse: Use ClickHouse monitoring tools or build your own monitoring checks to ensure the database is performing well and the data is up-to-date.