AWS IoT Events reference for inputs and variables in expressions - AWS IoT Events

AWS IoT Events reference for inputs and variables in expressions

Inputs

$input.input-name.path-to-data

input-name is an input that you create using the CreateInput action.

For example, if you have an input named TemperatureInput for which you defined inputDefinition.attributes.jsonPath entries, the values might appear in the following available fields.

{
    "temperature": 78.5,
    "date": "2018-10-03T16:09:09Z"
  }

To reference the value of the temperature field, use the following command.

$input.TemperatureInput.temperature

For fields whose values are arrays, you can reference members of the array using [n]. For example, given the following values:

{
    "temperatures": [
      78.4,
      77.9,
      78.8
    ],
    "date": "2018-10-03T16:09:09Z"
  }

The value 78.8 can be referenced with the following command.

$input.TemperatureInput.temperatures[2]
Variables

$variable.variable-name

The variable-name is a variable that you defined using the CreateDetectorModel action.

For example, if you have a variable named TechnicianID that you defined using detectorDefinition.states.onInputEvents.actions.setVariable.variableName, you can reference the (string) value most recently given to the variable with the following command.

$variable.TechnicianID

You can set the values of variables only using the setVariable action. You can't assign values for variables in an expression. A variable can't be unset. For example, you can't assign it the value null.

Note

In references that use identifiers that don't follow the (regular expression) pattern [a-zA-Z][a-zA-Z0-9_]*, you must enclose those identifiers in backticks (`). For example, a reference to an input named MyInput with a field named _value must specify this field as $input.MyInput.`_value`.

When you use references in expressions, check the following:

  • When you use a reference as an operand with one or more operators, make sure that all data types that you reference are compatible.

    For example, in the following expression, integer 2 is an operand of both the == and && operators. To ensure that the operands are compatible, $variable.testVariable + 1 and $variable.testVariable must reference an integer or decimal.

    In addition, integer 1 is an operand of the + operator. Therefore, $variable.testVariable must reference an integer or decimal.

    ‘$variable.testVariable + 1 == 2 && $variable.testVariable’

  • When you use a reference as an argument passed to a function, make sure that the function supports the data types that you reference.

    For example, the following timeout("time-name") function requires a string with double quotes as the argument. If you use a reference for the timer-name value, you must reference a string with double quotes.

    timeout("timer-name")
    Note

    For the convert(type, expression) function, if you use a reference for the type value, the evaluated result of your reference must be String, Decimal, or Boolean.

AWS IoT Events expressions support integer, decimal, string, and Boolean data types. The following table provides a list of incompatible pairs of types.

Incompatible pairs of types

Integer, string

Integer, Boolean

Decimal, string

Decimal, Boolean

String, Boolean