MSSQL

MSSQL is the protocol used to connect to Microsoft’s SQL Server.

Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications, which may run either on the same computer or on another computer across a network.

The Connectware MSSQL protocol enables to read from or write to a database on the database server.

Usage

In general, the MSSQL 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 MS SQL Server, at least the usual server connection properties are needed when specifying the Cybus::Connection resource:

• Host name

• Port

• User name

• Password

• Database to be used in this connection

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 Service Commissioning File Example below.

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

Reading Data

To read data from an MSSQL database, an endpoint has to be defined with either read or subscribe properties, including the definition of the intended SQL query. 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:

mssqlQuery1:
  type: Cybus::Endpoint
  properties:
    protocol: Mssql
    connection: !ref mssqlConnection
    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 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. If no placeholders are defined, the query will simple 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.

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. The endpoint definition includes the definition of the SQL query.

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 placeholders 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:

mssqlQuery1:
  type: Cybus::Endpoint
  properties:
    protocol: Mssql
    connection: !ref mssqlConnection
    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:

Important

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 MSSQL 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 MSSQL 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

mssql-example.yml

mssql-example.yml

---
description: >
  Sample MSSQL service commissioning file

metadata:
  name: Sample MSSQL 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:
  mssqlHost:
    type: string
    default: 127.0.0.1

  mssqlPort:
    type: integer
    default: 1433

  mssqlUser:
    type: string
    default: sa

  mssqlPassword:
    type: string
    default: SomeLongSecurePassw0rd

  mssqlDatabase:
    type: string
    default: tempdb

  initialReconnectDelay:
    type: integer
    default: 1000

  maxReconnectDelay:
    type: integer
    default: 30000

  factorReconnectDelay:
    type: integer
    default: 2

resources:
  mssqlConnection:
    type: Cybus::Connection
    properties:
      protocol: Mssql
      connection:
        host: !ref mssqlHost
        port: !ref mssqlPort
        username: !ref mssqlUser
        password: !ref mssqlPassword
        database: !ref mssqlDatabase
        connectionStrategy:
          initialDelay: !ref initialReconnectDelay
          maxDelay: !ref maxReconnectDelay
          incrementFactor: !ref factorReconnectDelay

  mssqlQuery1:
    type: Cybus::Endpoint
    properties:
      protocol: Mssql
      connection: !ref mssqlConnection
      subscribe:
        query: 'SELECT name FROM sys.databases'
        # Be very careful with this setting. A low value might overload
        # the database (the unit is milliseconds!).
        interval: 2000

  mssqlQuery2:
    type: Cybus::Endpoint
    properties:
      protocol: Mssql
      connection: !ref mssqlConnection
      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 (some_column) VALUES (@someValue)'

  mapping:
    type: Cybus::Mapping
    properties:
      mappings:
        - subscribe:
            endpoint: !ref mssqlQuery1
          publish:
            topic: 'system-tables'
        - subscribe:
            topic: 'insert-test'
          publish:
            endpoint: !ref mssqlQuery2

Footnotes

[1]

The regular expression for the identifiers of a placeholder is @[a-zA-Z0-9_]+, i.e. one single at-character @ followed by an identifier consisting of ascii characters, numbers, and the underscore. If there is more than one at-character in a row, such as in @@VERSION, the at-character sequence will not be interpreted as the beginning of a placeholder but instead it will be passed on unchanged. If one single at-character is followed by any other non-matching character, such as a whitespace or some punctuation, the at-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.)