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Client-side rules

Groovy right in the form: calculated values, dynamic field/button states and functions via the context.

REFERENZ LOW-CODE UPDATED: JUL 2026 APPLIES TO NUCLOS 4.2026.X

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What are client-side rules?

Client-side rules are Groovy expressions that react directly in the form – for calculated values, dynamic properties (e.g. field active/inactive, background colour) and buttons. They are defined on the layout or the business object.

Namespaces and packages

A namespace is defined per Nuclet (local identifier). Business objects without a Nuclet use the default namespace DEF. Packages enable Spring-managed library rules (callable functions).

Access via `context`

In code you access data via the context variable and expressions. [entity] is the internal name of the business object:

#{[namespace].[entity]}          // aktuelles BO / Unterformular-Datensätze als Liste
#{[namespace].[entity].[field]}  // Wert eines Attributs
#{[namespace].[entity].[field].id}      // Id eines Referenzfelds (java.lang.Long)
#{[namespace].[entity].[field].context} // Context eines referenzierten Objekts

The script runs when a new record is created or a field it reads changes. Example – sum a total across a subform:

def brutto = new java.math.BigDecimal(0.000)
context."#{WAR.auftrag_position}".each { item ->
    brutto = brutto.add(java.math.BigDecimal.valueOf(
        item."#{WAR.auftrag_position.gesamtpreisrechnung}"))
}
return brutto.setScale(4, java.math.RoundingMode.HALF_UP).doubleValue()

Dynamic properties (active/inactive)

A boolean return value controls „edit/new/delete/clone active“ and buttons: return true = active, return false = inactive.

Mind the context

The base context for new active is the parent BO of the subform, but for edit/delete/clone active it is the subform BO itself. To read the order status from a position, first go one context up (.context).

Functions via library rules

A library rule annotated with @Component (Spring) and a method annotated with @Function("name") can be called via context."#FUNCTION{name}"(...). The package namespace and package name must match; parameter/return types must fit.

Best practices & debugging

Read a field from the parent object (the field must exist in the layout, may be disabled):

stateNumeral = context."#{NUC.Rechnungsposition.rechnung.context}"."#{NUC.Rechnung.nuclosStateNumber}"

Log output with log.info("...") (Window → Output/Scripting).
Current user via the username variable (Nuclos 4.0.15+).
Groovy exceptions are not passed to the user – catch them and show a JOptionPane message box for debugging.