.. _user/protocols/mssql: ****************** MSSQL ****************** Overview ======== 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 :ref:`protocols/mssql/example-commissioning-file` below. More details about the connection properties are described below: :ref:`user/protocols/mssql_connection` 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: .. code-block:: yaml 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. .. code-block:: javascript { "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 [#f1]_. 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. .. code-block:: yaml 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: .. code-block:: javascript { "lastname": "Miller" } will return results filtered based on the where clause configured: .. code-block:: javascript { "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 [#f1]_. 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: .. code-block:: yaml 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: .. code-block:: yaml 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: .. code-block:: json { "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. .. code-block:: json [ { "name": "Alice", "lastname": "Miller", "gender": "female" }, { "name": "John", "lastname": "Clark", "gender": "male" } ] .. important:: 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 .. _user/protocols/mssql_connection: .. include:: ../protocolSchemas/MssqlConnection.rst .. _user/protocols/mssql_endpoint: .. include:: ../protocolSchemas/MssqlEndpoint.rst .. _protocols/mssql/example-commissioning-file: Example Commissioning File ========================== Download: :download:`mssql-example.yml` .. literalinclude:: mssql-example.yml :language: yaml :linenos: .. rubric:: Footnotes .. [#f1] 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.)