SQL

The SQL connector enables Connectware to communicate with relational databases. This implementation uses Sequelize (https://sequelize.org/), a Node.js ORM (Object-Relational Mapping) tool, to provide read, write, and subscribe capabilities for database operations.

Supported databases

• MariaDB

• PostgreSQL

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, you must provide 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'

We recommend defining these properties as parameters in the service commissioning file and reference them in the connection settings using !ref, so that the actual value can be edited at deployment time. See Service Commissioning File Example below.

For more information, see 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 an 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 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"
    }
  ]
}

Placeholder Syntax

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 placeholders. 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 be executed as-is.

Placeholder naming rules:

The regular expression for placeholder identifiers is $[a-zA-Z0-9_]+. This means:

• Placeholders start with a single dollar sign $

• Followed by an identifier consisting of ASCII letters, numbers, and underscores

• Examples: $name, $user_id, $value123

Special cases:

• Multiple dollar signs (e.g., $$VERSION) are not interpreted as placeholders and will be passed unchanged to the SQL query.

• A single dollar sign followed by whitespace or punctuation (e.g., $ or $.) is not interpreted as a placeholder.

• To use a single $ that matches the pattern above in the SQL query, define it as a placeholder and send the desired string as a value in the message payload.

Usage requirements:

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 dollar sign $ followed by an identifier is used to denote placeholders (see Placeholder Syntax for details). 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 an 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

Service Commissioning File Example

2KB

sql-example.yml

Open

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