SQL

This protocol implementation is a wrapper around the excellent Node.js ORM (Object-Relational Mapping tool) Sequelize (https://sequelize.org/)

It provides read, write and subscribe capabilities to most common databases.

Currently, only MariaDB and Postgres are supported.

Usage

In general, the implementation works by specifying a query or query template.

The following examples use a sample table called people that looks like this:

id	name	lastname	gender
1	Alice	Miller	female
2	Bob	Jones	male

Connection

To connect to a database, we only need a URL when specifying the Cybus::Connection resource:

<schema>://<user>:<password>@<host>:<port>/<database>

For example, to connect to a MariaDB database use this:

'mariadb://johndoe:my-secret-pw@localhost:3306/test'

To connect to a Postgres database use this:

'postgres://johndoe:my-secret-pw@localhost/test'

It is recommended to define these properties as parameters in the commissioning file and reference them in the connection settings using !ref, so that the actual value can be edited at deployment time. See Example Commissioning File below.

More details about the connection properties are described below: Connection Properties

Reading Data

To read data from a database, an endpoint has to be defined with either read or subscribe properties. Subscribe works by defining a polling interval, hence the query will be executed on a regular basis. Read is executed each time a MQTT message is sent to the respective endpoint topic with the /req (request) suffix, where the result is sent to the endpoint topic with the /res (result) suffix. The result of the query is provided in JSON format on the MQTT broker.

Example endpoint definition:

sqlQuery1:
    type: Cybus::Endpoint
    properties:
        protocol: Sql
        connection: !ref sqlConnection
        subscribe:
            query: 'SELECT * FROM people'
            interval: 2000

This endpoint will execute the given query and return the data as MQTT messages like in the following example. If no rows are returned, you will receive an empty array ([]) as a value.

{
  "timestamp": 1231782312, // unix timestamp in ms
  "value": [
    {
      "id": 1,
      "name": "Alice",
      "lastname": "Miller"
      "gender": "female"
    },
    {
      "id": 2,
      "name": "Bob",
      "lastname": "Jones"
      "gender": "male"
    }
  ]
}

The SQL query definition can be defined as a template string containing placeholders in the WHERE clause. In the template, the dollar sign character $ followed by an identifier is used to denote such placeholders [1]. The placeholders will be replaced by the values from the payload of the JSON message received via MQTT. If no placeholders are defined, the query will simply be executed as-is.

If the SQL query contains placeholder definitions, all their names must exist in the message payload, otherwise an error will be logged and the message will be ignored. The value of the placeholders must have the right data format matching the target schema of the database.

Example endpoint definition:

sqlQuery1:
    type: Cybus::Endpoint
    properties:
        protocol: Sql
        connection: !ref sqlConnection
        read:
            query: 'SELECT * FROM people WHERE lastname = $lastname'

Sending a message to the /req topic of this Endpoint with the following payload:

{ 'lastname': 'Miller' }

will return results filtered based on the where clause configured:

{
  "timestamp": 1231792312, // unix timestamp in ms
  "value": [
    {
      "id": 1,
      "name": "Alice",
      "lastname": "Miller"
      "gender": "female"
    }
  ]
}

Output Format on Read

When data is read from SQL results are published to the /res topic of the Endpoint. The output message is an object with two properties:

• timestamp: is the unix timestamp, in milliseconds, of when the read was executed

• value: is an array of results as returned by the SQL query

Writing Data

To write data to the database, an endpoint with write properties has to be defined. This endpoint needs the definition of an SQL query with a query template containing variables. The variables will be filled by the values of the payload of the JSON message received via MQTT.

In the SQL query definition, the query syntax is used as a template string containing placeholders. In the template, the at-character $ followed by an identifier is used to denote such placeholders [1]. The placeholders will be replaced by the values from the payload of the JSON message received via MQTT.

All specified template variables must exist in the payload and must have the right target format matching the schema of the database.

Example endpoint definition:

sqlQuery1:
    type: Cybus::Endpoint
    properties:
        protocol: Sql
        connection: !ref sqlConnection
        write:
            query: 'INSERT INTO people (name, lastname, gender) VALUES ($name, $lastname, $gender)'

When using bulk insert you need to specify the endpoint like this:

sqlQuery2:
    type: Cybus::Endpoint
    properties:
        protocol: Sql
        connection: !ref sqlConnection
        write:
            query: 'INSERT INTO people (name, lastname, gender) VALUES'
            queryValues: '($name, $lastname, $gender)'

To write data, you must send a MQTT message like the following to the /set topic of the Endpoint:

{
  "name": "Alice",
  "lastname": "Miller",
  "gender": "female"
}

Alternatively, you can also send multiple rows into a single message for performance reasons like this:

When using this method of insertion make sure all rows have the same amount of columns.

You will also need to specify the parameter queryValues in the endpoint definition.

[{ 'name': 'Alice', 'lastname': 'Miller', 'gender': 'female' }, { 'name': 'John', 'lastname': 'Clark', 'gender': 'male' }]

The SQL connection on the Connectware side does not perform any data validation against the database schema. The senders of the MQTT messages themselves must ensure to send the data in the correct format.

Output Format on Write

When data is written to an SQL Endpoint a message is published to the /res topic of the Endpoint. The output message is an object with two properties:

• timestamp: is the unix timestamp, in milliseconds, of when the write was executed

• value: is set to true when the write was successful

Connection Properties

Endpoint Properties

Example Commissioning File

Download:

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sql-example.yml

---
description: >
    Sample SQL service commissioning file

metadata:
    name: Sample SQL service
    icon: https://www.cybus.io/wp-content/uploads/2017/10/for-whom1.svg
    provider: cybus
    homepage: https://www.cybus.io
    version: 1.0.0

parameters:
    sqlURL:
        type: string
        default: 'mariadb://root:my-secret-pw@localhost:3306/mysql'
    initialReconnectDelay:
        type: integer
        default: 1000
    maxReconnectDelay:
        type: integer
        default: 30000
    factorReconnectDelay:
        type: integer
        default: 2

resources:
    sqlConnection:
        type: Cybus::Connection
        properties:
            protocol: Sql
            connection:
                url: !ref sqlURL
                connectionStrategy:
                    initialDelay: !ref initialReconnectDelay
                    maxDelay: !ref maxReconnectDelay
                    incrementFactor: !ref factorReconnectDelay

    sqlQuery1:
        type: Cybus::Endpoint
        properties:
            protocol: Sql
            connection: !ref sqlConnection
            subscribe:
                query: 'SELECT User FROM user'
                # Be very careful with this setting. A low value might overload
                # the database (the unit is milliseconds!).
                interval: 2000

    sqlQuery2:
        type: Cybus::Endpoint
        properties:
            protocol: Sql
            connection: !ref sqlConnection
            write:
                # Here we use the placeholder $someValue. The protocol driver will insert
                # the value from the input JSON message under the key someValue
                query: 'INSERT INTO test (id, some_column) VALUES ($id, $someValue)'

    mapping:
        type: Cybus::Mapping
        properties:
            mappings:
                - subscribe:
                      endpoint: !ref sqlQuery1
                  publish:
                      topic: 'database-users'
                - subscribe:
                      topic: 'database-insert-test'
                  publish:
                      endpoint: !ref sqlQuery2

Footnotes

[1]

The regular expression for the identifiers of a placeholder is $[a-zA-Z0-9_]+, i.e. one single dollar sign character $ followed by an identifier consisting of ascii characters, numbers, and the underscore. If there is more than one dollar sign character in a row, such as in $$VERSION, the dollar sign character sequence will not be interpreted as the beginning of a placeholder but instead it will be passed on unchanged. If one single dollar sign character is followed by any other non-matching character, such as a whitespace or some punctuation, the dollar sign character sequence will also not be interpreted as the beginning of a placeholder and it will be passed on unchanged. (If you need one single $ that matches the above pattern in the resulting SQL query, currently this requires defining an extra placeholder and sending the desired string as a value for the replacement in the message payload.)