Property change (CHANGE)

The property change operator allows you to change the values of one property (write) to the value of another property (read) for all object collections for which the value of a third property (condition) is not NULL. The condition can be omitted (in which case it is considered to be equal to TRUE).

Changeable properties

In general, the property to be written should be data, but the platform also allows writing to properties created using the selection operator. In this case, the platform determines the condition that is met in this selection operator for the created property; the property corresponding to that condition is written to. Accordingly, all properties that can be written to we'll call mutable.

info

In addition to the above, mutable properties are also properties created using the extremum operator and logical operators (which are basically varieties of the selection operator)

Language

To declare an action that implements property change, use the CHANGE operator.

Examples

// set a 15 percent discount for all customers who have an order amount over 100
CLASS Customer;
discount = DATA NUMERIC[5,2] (Customer);
totalOrders = DATA NUMERIC[14,2] (Customer);
setDiscount  {
    discount(Customer c) <- 15 WHERE totalOrders(c) > 100;
}

discount = DATA NUMERIC[5,2] (Customer, Item);
in = DATA BOOLEAN (Item);
// change the discount for selected products for a customer
setDiscount (Customer c)  {
    discount(c, Item i) <- 15 WHERE in(i);
}

// copy property g to property f
f = DATA INTEGER (INTEGER);
g = DATA INTEGER (INTEGER);
copyFG  {
    f(a) <- g(a);
}