astra_esp8266

Introduction

Access a Cassandra database from an ESP8266 or ESP32. The astra_esp8266 library provides basic operations to connect with a Datastax Astra database. The libray also tries to provided "greased" paths for various common use cases such as basic key/value storage and storing time series sensor data.

Installation

To install into your Arduino IDE, follow the instructions available on ArduBadge.

Prereqs

• Astra Database: This library requires a Datastax Astra database which is built on top of Cassandra. The free tier of the database will be more than adequate for most uses. To create an Astra database, go to https://astra.datastax.com/ and follow the instructions to register and create a database.

Examples

Key/Value Storage

It is easy to use an Astra database as a basic key/value store. The keyValStore example shows how to connect to an Astra database, write some data to the database, and then read back data from the database. In order to be able to connect to your wifi network and also your Astra database, the following const char* values need to be set:

• ssid
• password
• dbId
• dbRegion
• dbUser
• dbPassword

The comments in keyValStore.ino should describe what information needs to be specified. Once the file has been updated with your own information, the sketch should be ready to compiled, uploaded, and run.

The Astra KeyValStore client can be easily embedded into any sketch where you need to store or retrieve simple key/val type data. The client takes care of creating the database table--the table name is "kvstore" if you want to access it via CQL (see the Astra website for different ways to access your database).

Adding Rows to a Table

It is possible to go beyond key/value storage and add arbitrary rows to an existing table. The addRowToTable example shows how to do exactly that. The example is loosely based on the Moby Name Generator which can generate names for Docker containers. The example requires a table created like:

	 CREATE TABLE IF NOT EXISTS containernames (
	   adjective text,
	   surname text,
	   randval int,
	   PRIMARY KEY ((adjective), surname)
	   );

The comments in addRowToTable.ino should describe what information needs to be specified. Once the file has been updated with your own information, the sketch should be ready to compiled, uploaded, and run.

The Astra client can be easily embedded into any sketch where you need to write data into a database from an ESP8266.

Timeseries Data

Storing timeseries data from multiple IOT type sensors has become common. The timeseries example shows how to store sensor data and associated time data into an Astra database. In order to get an accurate time, additional libraries are required including "NTPClient" (by Fabrice Weinberg) and "Time" (by Michael Margolis). The example assumes a table that was created like:

	 CREATE TABLE IF NOT EXISTS jikandata (
	   sensorid text,
	   year int,
	   month int,
	   day int,
	   hour int,
	   minute int,
	   second int,
	   data int
	   PRIMARY KEY ((sensorid, year, month), day, hour, minute, second)
	   ) WITH CLUSTERING ORDER BY (day DESC, hour DESC, minute DESC, second DESC);

With this approach a single partition with hold a month of data and the reversed fields make it easy to do a "latest" select. Depending on the amount of data coming in from each sensor, the primary key could just include the sensorid and year to store a full year of data in a single partition.

This example stores random integers into the data column, but presumably there could be one or more data columns which are populated with data from sensors.