NESTEDSESSION operator

The NESTEDSESSION operator creates an action that executes the other action in a nested session.

Syntax

NESTEDSESSION [SINGLE] action

Description

The NESTEDSESSION operator creates an action that executes the other action in a nested session. Applying changes inside the nested session copies them back into the surrounding session rather than committing to the database.

Parameters

• SINGLE

  Optional keyword. If the NESTEDSESSION is itself called inside an apply transaction, this flag is propagated to the inner action: changes to stored properties used by it are flushed incrementally during the transaction instead of being batched at the end of the apply.

• action

  A context-dependent action operator that defines an action to be executed in the nested session.

Examples

testNestedSession ()  {
    NESTEDSESSION {
        name(Sku s) <- 'aaa';
        // in fact, the changes will not be applied to the database, but to the "upper" session
        APPLY; 
    }

    MESSAGE (GROUP SUM 1 IF name(Sku s) == 'aaa'); // returns all rows
    CANCEL;
    // returns NULL if there was no Sku named aaa in the database before
    MESSAGE (GROUP SUM 1 IF name(Sku s) == 'aaa'); 

}

FORM sku
    OBJECTS s = Sku PANEL
    PROPERTIES(s) id, name
;
newNestedSession()  {
    NESTEDSESSION {
        NEW s = Sku {
            // shows the form, but any changes in it will not be applied to the database, 
            // but will be saved in the "upper session" session
            SHOW sku OBJECTS s = s;
        }
    }
}

// SINGLE — only meaningful when NESTEDSESSION is itself executed inside an apply transaction
recalcNested ()  {
    APPLY {
        NESTEDSESSION SINGLE {
            // changes here are flushed incrementally during the outer apply
            name(Sku s) <- 'recalculated';
        }
    }
}