IAP/MQ Connections support type conversions between source and destination types to support connections between sources of one type and destinations of another. All sources and all destinations must themselves be assignment-compatible.
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For example, this simple map transforms a value of standard type SNVT_switch to one of standard type SNVT_lev_percent:
| { "$": "$.value" } |
Key “$” addresses the entire value. Its value is “value”, which references a “value” property within the source datapoint value. “$” addresses the entire source or destination item. A dotted notation addresses nested properties such as “top.left.x”.
This is the identity map:
| { "$": "$" } |
Transformation objects support more complex operations such as type casts or transformation expressions. The following map produces a datapoint value of standard type SNVT_switchfrom a datapoint value of the standard scalar type SNVT_lev_percent:
| { value: "$", state: { transform: "$ ? 0 : 1" } } |
The first production assigns the entire source value, addressed as “$”, to the destination value property. The second production specifies a transformation with a ternary operator.
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The following map converts a value of type SNVT_switch into a simple string presentation:
| { "$": { transform: "$.value + ' ' + $.state" } } |
Transformations support all non-modifying Javascript operators (see developer.mozilla.org). Pre- and post-decrement and increment operators (++, --) have no effect.
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The following numeric functions are available:
| Function | Result | Description |
|---|---|---|
| abs(v) | v if v ≥ 0, else -v | Absolute of a value |
| min(v, w) | v if v ≤ w, else w | Minimum of two values |
| max(v, w) | v if v ≥ w, else w | Maximum of two values |
| sqrt(v) | Square root of v | Square root function |
| pow(v, w) | v to the power w | Power function |
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| Function | Result | Comment |
|---|---|---|
| length(s) | Number of characters in s or 0 (zero) if none. | |
| upper(s) | The upper case version of s. | s remains unchanged |
| lower(s) | The lower case version of s. | s remains unchanged |
| substr(s, i, l) | The substring in s starting with zero-based index I and of length l characters. | s remains unchanged |
| match(s, r ) | A Boolean result indicating whether s matched ECMAScript 6 regular expression r. | Example: match(“test”, “[a-z]{4}”) |
The Constant Transformation Type
The $ object represents the source datapoint value.
This constant type map produces a SNVT_switch from a scalar SNVT_lev_percent input, where the destination “state” field is constant:
| { value: "$", state: { constant: "ST_ON" } } |
The constant value is copied into the destination verbatim. The constant transformation is more efficient than an equivalent transform.
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The enumeration type maps two different yet compatible enumerations:
| { value: "$", state: { enumeration: { source: "$", // the source enumeration value map: { 1: -1, // source 1 becomes destination -1, 0: 0, // source 0 remains 0 (the default), -1: 2 // source -1 becomes destination 2 } // map } // enum } // state } // map |
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The source property of an enumeration transformation can also be evaluated as an expression. The following example maps the preset value into the preset name:
| { source: { “ON”: ”ON”, “MID”: “MID”, “OFF”: “OFF } // map } // enum } // source } |
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