OPC UA API reference

OPC UA connector programming specifications for FairCom Edge

FairCom provides special API actions for OPC UA connectors and transforms. The OPC UA service must be enabled in order to complete FairCom OPC UA actions.

Note A return value of 0 signals the successful completion of an action.

 

Request examples

Note The FairCom createInput JSON action is used to define the specifics of a connector device and the desired data.

Minimal

{
  "action": "createInput",
  "params": {
    "inputName": "opcDS1",
    "serviceName": "opcua",
    "settings": {
      "opcServerUrl": "opc.tcp://MyOPCDevice.com:4840",
      "propertyMapList": [
        {
          "propertyPath": "the_answer",
          "opcNamespace": 1,
          "opcNodeName": "the.answer"
        }
      ]
    },
    "tableName": "opcTable1"
  },
  "authToken": "replaceWithAuthTokenFromCreateSession"
}
 
 

Maximal

{
  "requestId": "19",
  "api": "hub",
  "apiVersion": "1.0",
  "action": "createInput",
  "params": {
    "inputName": "opcDS2",
    "serviceName": "opcua",
    "dataPersistenceStrategy": "onChange", 
    "dataCollectionIntervalMilliseconds": 5000,
    "immediatelyCollectDataOnStart": true,
    "dataCollectionBufferCount": 2,
    "settings": {
      "opcServerUrl": "opc.tcp://MyOPCDevice.com:4840",
      "opcServerUser": "MyUser",
      "opcServerPassword": "MyPassword",
      "propertyMapList": [
        {
          "propertyPath": "temperature",
          "opcNamespace": 1,
          "opcNodeName": "OPC-temperature-datasource"
        },
        {
          "propertyPath": "humidity",
          "opcNamespace": 1,
          "opcNodeName": "OPC-humidity-datasource"
        },
        {
          "propertyPath": "pressure",
          "opcNamespace": 1,
          "opcNodeName": "OPC-pressure-datasource"
        },
        {
          "propertyPath": "quality",
          "opcNamespace": 1,
          "opcNodeName": "OPC-quality-datasource"
        }
      ]
    },
    "ownerName": "admin",
    "tableName": "opcTable2",
    "databaseName": "faircom",
    "retentionPolicy": "autoPurge",
    "retentionPeriod": 30,
    "retentionUnit": "day",
    "metadata": {
    }
  },
  "authToken": "replaceWithAuthTokenFromCreateSession"
}
 
 

 

Properties

Request properties ("params")

Property Description Default Type Limits (inclusive)

databaseName

The "databaseName" property specifies the database that contains an object, such as a table or code package. If it is set to null or is omitted, it defaults to the default database of the JSON Action session, see "createSession" and the "defaultDatabaseName" property. 

You specify this property when you want to use a different database instead of the default. Your session's account must have the appropriate privileges to access the code package.

This property is useful because objects, such as tables and code packages, can have the same name in multiple databases. This feature allows you to create multiple environments in the same server and reuse the same JSON actions in each environment. For example, you can create "dev", "test", "stage", and "prod" databases on the same server and use the "defaultDatabaseName" or "databaseName" properties to specify the desired environment.

It is an error to set "databaseName" to the empty string "".

If no default database is specified during "createSession", the server sets the "defaultDatabaseName" to the "defaultDatabaseName" value specified in the services.json file.

 Defaults to the session's "defaultDatabaseName" property string 1 to 64 bytes

dataCollectionBufferCount

The "dataCollectionBufferCount" property specifies the number of times the collector retrieves and caches data from the device before writing the data to the integration table.

This option combines multiple data collection events and inserts them into the integration table as one MQTT message.

If this value is more than 1, the connector converts each set of collected data into a JSON object and adds the object to an array inside a JSON document. When the count is reached, the connector writes the JSON document to the source_payload field of a record it inserts into the integration table.

 Optional with default of 1 integer 1 to 65535

dataCollectionIntervalMilliseconds

The "dataCollectionIntervalMilliseconds" property schedules the connector to collect data periodically using the specified number of milliseconds. 

 Optional with default of 10000 (10 seconds). integer 0 and negative values are invalid.

dataPersistenceStrategy

The "dataPersistenceStrategy" property controls when a connector writes collected data to a record in the input table specified by "tableName". 

  • The "onSchedule" setting causes the connector to persist each collected value, which occurs on the schedule set by the "dataCollectionIntervalMilliseconds" property. This setting is useful for continuously collecting device data for trend analysis and machine learning.
  • The "onChange" setting causes the connector to collect data on the schedule set by the "dataCollectionIntervalMilliseconds" property, but it only persists data when it changes. This allows the connector to detect and store data changes as events, such as alerts and status updates. This setting greatly reduces data storage for infrequently changing telemetry, such as changes to a temperature sensor.

Note The connector misses events when its data collection schedule is not frequent enough to see data changes. Thus, the "onChange" setting makes a polling protocol, such as Modbus, behave like a push protocol, but it is not a push protocol like MQTT.

 Optional with default of "onSchedule" string

"onSchedule"

"onChange"

enabled

 The "enabled" property turns on or off an input or output connector. Thus, it pauses or starts data collection or delivery. Optional with default of true Boolean

true

false

enabledFilter

 The "enabledFilter" property returns input connections that are enabled or not. Omit or set to null to match all connections. Optional with default of null Boolean

true

false

immediatelyCollectDataOnStart

The "immediatelyCollectDataOnStart" property controls how a connector first collects data after being started.

  • When true, it immediately collects and stores data and thereafter collects data according to the strategy specified in "dataPersistenceStrategy". In other words, it ignores the "dataPersistenceStrategy" for the initial data collection event and unconditionally stores the first set of data it collects. This setting allows subscribers to receive an initial data collection message each time the server or connector starts, which is useful for systems that display live status information.
  • When false, which is the default, it collects data according to the strategy specified in "dataPersistenceStrategy". For example, when the "dataPersistenceStrategy" is "onChange", the connector collects data on a schedule and persists it only when the data changes - even after a restart.
 Optional with default of false Boolean

true

false

inputName

The "inputName" property specifies the unique name of an input. A FairCom generated name follows the pattern "Input #n from <pluginName> to <databaseName>.<ownerName>.<tableName>".

"params": {
    "inputName": "modbusTCP",
    "serviceName": "modbus"
}

Required - No default value

 string 1 to 100 bytes

metadata

 The "metadata" property contains user-defined properties that add keywords and tags about the code package. The server indexes this field with a full-text index so you can search for any word or phrase to find code packages. Optional with default of {} object 0 or more key/value pairs

ownerName

The "ownerName" property specifies the account that owns an object, such as a table or code package. See "createSession" and the "defaultOwnerName" property for more details. 

You specify this property when you want to use a different account instead of the default. Your session's account must have the appropriate privileges to access the code package. 

This property is useful because objects, such as tables and code packages, can have the same name in the same database as long as different accounts own each object. This feature allows you to create duplicate objects for different users on the same server and reuse the same JSON actions on those objects. For example, an administrator can copy objects from a production environment to her account so she can troubleshoot an issue using the same JSON actions, JavaScript, and SQL code.

It is an error to set "ownerName" to the empty string "".

If no default owner is specified during "createSession", the server sets the "defaultOwnerName" to the "defaultOwnerName" value specified in the services.json file.

 Optional with default of the session's "defaultOwnerName" property string 1 to 64 bytes

retentionPeriod

The "retentionPeriod" property specifies how many units of data to retain. It refers to the unit of time specified by the "retentionUnit" property. For more details, see "retentionPeriod".

Optional with default of 30

 integer 1 to 100

retentionPolicy

The "retentionPolicy" property controls how messages are persisted. 

If not specified, the default found in the services.json file is used. Initially, it is "autoPurge".

 

retentionPolicy values:
  • "autoPurge"
    • This is the default. It is automatically applied when a new topic is created. It is preferred because it allows FairCom's servers to automatically remove messages that are older than the retention time. This helps ensure message data does not consume all storage space. It also minimizes storage costs and speeds up data access. The server partitions a table into multiple files so it can efficiently delete expired files.
  • "neverPurge"
    • This stores messages on disk and never removes them. This is useful when you need the entire history of the message stream. If message velocity is high, this can consume all storage space and cause an outage. The server creates a non-partitioned table, which is slightly faster than a partitioned table because it stores all records in one file.

Optional with default of "autoPurge"

 string

"autoPurge"

"neverPurge"

retentionUnit

The "retentionUnit" property specifies a unit of time that the server will use to purge expired messages. For example, if you want a week's worth of messages to be purged once a week, set "retentionUnit" to "week". This property is optional.

If not specified, the default found in the services.json file is used. Initially, it is "week". 

  • This property is used in concert with "retentionPeriod" to determine retention time.
  • "retentionUnit" values:
    • "minute"
    • "hour"
    • "day"
    • "week"
    • "month"
    • "year"
    • "forever"

Note 

  • For best performance, set the "retentionUnit" to a value that keeps "retentionPeriod" between 5 and 30. 
  • When you set "retentionUnit" property to "forever" the server will not purge messages. This setting is the same as setting "retentionPolicy" to "neverPurge".
  • The "retentionUnit" and "retentionPeriod" properties are used only when the "retentionPolicy" is set to "autoPurge".

Optional with default of "day"

string

"minute"

"hour"

"day"

"week"

"month"

"year"

runningFilter

 The "runningFilter" property returns input connections that are running or not. Omit or set to null to match all connections. Optional with default of null Boolean

true

false

serviceName

The "serviceName" property contains the name of a FairCom input or output service. 

See the "params" topic of each specific service for the requirements of this property.

The following services are available as of the V5 release:
  • "MODBUS"
  • "SIEMENSUDT2JSON"
  • "OPCUA"

Note The SQL, JSON RPC, and REST services can automatically query any integration table in FairCom's servers without requiring configuration.

MQTT always represents both input and output services. This is because once a topic is created and assigned to an integration table, any MQTT client can publish messages to it and subscribe to those messages.

 Required - No default value string 1 to 64 bytes

settings

The "settings" property contains properties that are specific for each connector type. Settings for Modbus are different than settings for OPC UA, and so forth. See the API reference "params" property of each connector for details of the "settings" property for that connector.

Connector-specific "settings"

 Optional with default of {} object

Allen-Bradley "params"

Modbus "params"

OPC UA "settings"

Siemens S7 "params"

settings

.opcServerPassword

 The "opcServerPassword" property specifies the password for your OPC UA device. Optional with default of "" string No limit

settings

.opcServerUrl

 The "opcServerUrl" property specifies the IP or URL to your OPC UA device, including the port. Required - No default value string No limit

settings

.opcServerUser

 The "opcServerUser" property specifies the username for your OPC UA device. Optional with default of "" string No limit

settings

.propertyMapList

 The "propertyMapList" property specifies which data the connector requests and where to put it in the generated JSON. Required - No default value array of objects

zero or more objects containing zero or more of the following properties:

"opcNamespace"

"opcNodeName"

"propertyPath"

settings

propertyMapList

.opcNamespace

 The "opcNamescpace" property specifies the OPC UA namespace that this variable exists in. Required - No default value int16 0 to 32767

settings

propertyMapList

.opcNodeName

 The "opcNodeName" property specifies the name of the OPC UA variable for this data. Required - No default value string No limit

settings

propertyMapList

.propertyPath

 The "propertyPath" property specifies the name of the data to be defined by "propertyValue". Required - No default value string 0 to 256 bytes

tableName

The "tableName" property contains the unique, user-defined name of a table.

See table name in System limits for the table naming requirements and limitations.

 

"params": {
  "tableName": "ctreeTable"
}
 Required - No default value string 1 to 64 bytes

 

Response properties ("result")

Property Description Type Limits (inclusive)

data

The "data" property contains a response message. Its contents are defined by the action. It is an empty array when no results are available. The following is an example of the data property from a code package action.

  "result": {
    "data": [
      {
        "codeId": 6,
        "databaseName": "faircom",
        "ownerName": "admin",
        "codeName": "convertAndCategorizeTemperature",
        "codeVersion": 1,
        "clonedCodeId": 1,
        "codeStatus": "active",
        "codeLanguage": "javascript",
        "serviceName": "javascript",
        "codeType": "module",
        "description": "optional new description",
        "metadata": {},
        "createdBy": "ADMIN",
        "createdOn": "2025-08-25T21:48:38.109",
        "updatedBy": "ADMIN",
        "updatedOn": "2025-08-25T21:48:38.109",
        "comment": "Cloned from convertTemperature",
        "codeFormat": "utf8"
      },
    ]
 array of objects The action determines its contents.

data

.enabled


The "enabled" property is true when a connector is allowed to connect to a device. It is false when a connector will not attempt to connect to the device.

 

 boolean true
false

data

.running

 The "running" property is true when an input connector is collecting data or an output connector is delivering data; otherwise, it is false. A disabled connector will never be running. An enabled connector may or may not be running. Boolean

true

false

data

.stopCode

 The "stopCode" property is 0 when the connector is successfully connected to its device or software; otherwise, it is non-zero. integer -2147483648 to 2147483647

data

.stopReason

 The "stopReason" property is "" when the input connector is collecting data; otherwise, it is a non-empty string. string 0 to 256 bytes

 

interface specification

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