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Version: 7.0

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, while NEW and DELETE specify resolution events for creating and deleting aggregated objects respectively.

The AGGR operator may appear only as a top-level property definition in the = statement. It cannot be used inside an expression, inside other operators, or inside the JOIN operator's [= ] form.

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;