Jam.py documentation

Navigating datasets

Each active dataset has a cursor, or pointer, to the current row in the dataset. The current row in a dataset is the one whose values can be manipulated by edit, insert, and delete methods, and the one, whose field values, data-aware controls on a form currently show.

You can change the current row by moving the cursor to point at a different row. The following table lists methods you can use in application code to move to different records:

Client method	Server method	Description
first	first	Moves the cursor to the first row in an item dataset.
last	last	Moves the cursor to the last row in an item dataset.
next	next	Moves the cursor to the next row in an item dataset.
prior	prior	Moves the cursor to the previous row in an item dataset.

In addition to these methods, the following table describes two methods that provide useful information when iterating through the records in a dataset:

Client method	Server method	Description
bof	bof	If the method returns true, the cursor is at the first row in the dataset, otherwise, the cursor is not known to be at the first row in the dataset.
eof	bof	If the method returns true, the cursor is at the last row in the dataset, otherwise, the cursor is not known to be at the last row in the dataset.

Each time the cursor move to another record in the dataset the following events are triggered:

Client event	Server event	Description
on_before_scroll	on_before_scroll	Occurs before an application scrolls from one record to another.
on_after_scroll	on_after_scroll	Occurs after an application scrolls from one record to another.

Using this methods we can navigate a dataset. For example,

on the client:

function get_customers(customers) {
    customers.open();
    while (!customers.eof()) {
        console.log(customers.firstname.value, customers.lastname.value);
        customers.next();
    }
}

on the server:

def get_customers(customers):
    customers.open()
    while not customers.eof():
        print customers.firstname.value, customers.lastname.value
        customers.next()

Shorter ways to navigate dataset

There is the each method on the client that can be used to navigate a dataset:

For example:

function get_customers(customers) {
    customers.open();
    customers.each(function(c) {
        if (c.rec_no === 10) {
            return false;
        }
        console.log(c.rec_no, c.firstname.value, c.lastname.value);
    });
}

On the server we can iterate dataset rows the following way:

def get_customers(customers):
    customers.open()
    for c in customers:
        if c.rec_no == 10:
            break
        print c.firstname.value, c.lastname.value

Both functions will output customer names for the first 10 records in the dataset.

In both cases the c and customers are pointers to the same object.