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. If the operator is executed during an apply transaction of the current session, no nested session is created — the executed action is deferred and executed in the current session inside the same transaction.

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';
        }
    }
}