AGGR operator

The AGGR operator creates an aggregation.

Syntax

AGGR [eventClause] aggrClass WHERE aggrExpr [NEW [newEventClause]] [DELETE [deleteEventClause]]

Description

In addition to the property that is the result of this operator and contains the value of the aggregated object, for each parameter the AGGR operator also creates a data property with one parameter of type aggrClass. The value class and name of this property match the class and name of the corresponding parameter; when the aggregated object is created, the value of the parameter is automatically written to this property.

eventClause specifies the base check event; NEW and DELETE specify resolution events for creating and deleting aggregated objects respectively.

Unlike other context-dependent operators, the AGGR operator cannot be used in expressions inside other operators (in this sense it is more like context-independent operators), or in the JOIN operator (inside [= ])

Parameters

• eventClause

  Event description block. The base check event. Default — global APPLY.

• aggrClass

  The value class of the aggregated object. Must be a user-defined class; built-in classes are not allowed.

• aggrExpr

  An expression whose non-NULL values drive the aggregation; its typed parameters determine the parameters of the result property and of the auto-created properties for each parameter.

• NEW

  Keyword. Specifies the resolution event for creating aggregated objects.

• newEventClause

  Event description block. If NEW is absent, the resolution event inherits only the scope (GLOBAL/LOCAL) of eventClause; its FORMS, AFTER/GOAFTER, and event name are not carried over. If NEW is specified but newEventClause is omitted, the default global APPLY event is used.

• DELETE

  Keyword. Specifies the resolution event for deleting aggregated objects.

• deleteEventClause

  Event description block. If DELETE is absent, the resolution event inherits only the scope (GLOBAL/LOCAL) of eventClause; its FORMS, AFTER/GOAFTER, and event name are not carried over. If DELETE is specified but deleteEventClause is omitted, the default global APPLY event is used.

Examples

CLASS A; CLASS B; CLASS C;
f = DATA INTEGER (A, B);
c = AGGR C WHERE f(A a, B b) MATERIALIZED INDEXED;

CLASS AB;
ab = AGGR AB WHERE A a IS A AND B b IS B; // for each A B pair creates an object AB

CLASS Shipment 'Delivery';
date = ABSTRACT DATE (Shipment);
CLASS Invoice 'Invoice';
createShipment 'Create delivery' = DATA BOOLEAN (Invoice);
date 'Shipment date' = DATA DATE (Invoice);
CLASS ShipmentInvoice 'Delivery by invoice' : Shipment;
// creating a delivery by invoice, if the option for delivery creation is defined for the invoice
shipment(Invoice invoice) = AGGR ShipmentInvoice WHERE createShipment(invoice);
date(ShipmentInvoice si) += sum(date(invoice(si)),1); // delivery date = invoice date + 1

// LOCAL base event: all three events run within the session
sessionAggr(Invoice invoice) = AGGR LOCAL ShipmentInvoice WHERE createShipment(invoice);

// explicit NEW event clause: creation runs locally, deletion inherits the base (global) event
newLocalAggr(Invoice invoice) = AGGR ShipmentInvoice WHERE createShipment(invoice) NEW LOCAL;

// separate events: creation — global (empty NEW clause defaults to APPLY), deletion — local
splitAggr(Invoice invoice) = AGGR ShipmentInvoice WHERE createShipment(invoice) NEW DELETE LOCAL;