Transforms

Transforms are a concept in Jayvee to define the transformation of individual values. They are similar to functions in programming languages, i.e. they perform computations on some input values and produce output values. Transform work by mapping input values to outputs using expressions.

Important

In its current state, Jayvee only supports a single input and a single output for transforms. For the future, it is planned to support arbitrary numbers of inputs and outputs.

Syntax

The general syntax of transforms looks like this:

transform <name> {
  from <inputName> oftype <inputValuetype>;
  to <outputName> oftype <outputValuetype>;

  <outputName>: <expression>;
}

The transform keyword is used to define a transform and give it a name. The curly braces denote the body of the transform.

The body first contains the definitions of input and output ports. Input ports are defined using the from keyword whereas output ports use the to keyword. Next, they are given a name and, after the oftype keyword, typed with a valuetype.

Below, there needs to be an output assignment for each output port. The output assignment defines how a particular output value is computed. They consist of the name of an output port, followed by a :. Next, an expression specifies how the output value shall be computed. Names of input ports can be used in such an expression to refer to input values.

Example

The following transform converts temperature values from degree Celsius to Kelvin:

transform CelsiusToKelvin {
  from tempCelsius oftype decimal;
  to tempKelvin oftype decimal;

  tempKelvin: tempCelsius + 273.15;
}

The following transform converts a text based status into a boolean value, true if the text is Active, false for any other value:

transform StatusToBoolean {
  from statusText oftype text;
  to statusBoolean oftype boolean;

  statusBoolean: statusText == "Active";
}

Applying transforms to table columns

Transforms can be applied to columns of a table. Please refer to the documentation of the TableTransformer block type to find out how.