Loop (FOR)

The loop operator creates an action that iterates all object collections for which the defined condition is met, and executes a defined action for each such object collection (let's call it the main one). You can also define an alternative action that will be executed only if no object collections have been found that meet the condition. The condition itself is defined as a certain property. Let's say that the condition is satisfied if the value of this property is not NULL.

The set of iterated object collections is fixed before the loop starts: the condition is evaluated once, the matching object collections are read, and the main action is then executed once per collection in that set. Changes made by the main action — even to the data underlying the condition — do not affect the set being iterated.

By default, object collections are iterated in arbitrary order. The developer can explicitly define this order by specifying a list of properties used as sort keys: object collections are compared by the value of the first property, ties are broken by the second property, and so on. The whole list is used in ascending order by default; the developer can request descending order, in which case it applies to the entire list.

As for other set operations, the condition must be such that the operation is correct.

Inside the main action, the interruption operator exits this loop, the next iteration operator moves to the next object collection in the same set, and the exit operator propagates outward, exiting the surrounding action call.

Adding an object

This operator also allows you to create an object of a specified concrete custom class for each iterated object collection. This object can then be used in the main action as a parameter.

Language

The syntax of the loop operator is described by the FOR operator.

Examples

name = DATA STRING[100] (Store);

testFor  {
    LOCAL sum = INTEGER ();
    FOR iterate(i, 1, 100) DO {
        sum() <- sum() (+) i;
    }

    FOR in(Sku s) DO {
        MESSAGE 'Sku ' + id(s) + ' was selected';
    }

    FOR Store st IS Store DO { // iterating over all objects of the Store class
        FOR in(st, Sku s) DO { // iterating over all Sku for which in is set
            MESSAGE 'There is Sku ' + id(s) + ' in store ' + name(st);
        }

    }
}

newSku ()  {
    NEW s = Sku {
        id(s) <- 425;
        name(s) <- 'New Sku';
    }
}

copy (Sku old)  {
    NEW new = Sku {
        id(new) <- id(old);
        name(new) <- name(old);
    }
}

createDetails (Order o)  {
    FOR in(Sku s) NEW d = OrderDetail DO {
        order(d) <- o;
        sku(d) <- s;
    }
}