For pushing changes from the database to the end user, the regular solution is using websockets. A change in a record is detected - using a trigger or using the CQN (Change Query Notification) feature - and a notification is send to a websocket server. That websocket server broadcasts the notification over a channel to all browsers that are tuned in to that websocket channel. Then the browser reacts to that notification, usually showing an alert or refreshing a report. This trick is described on multiple sites, just Google for "oracle apex websockets" or similar.
// onMessage is called when a message is received from the websocket server
// fetch the changed records
[Edit Jul 4 : I changed the code in a way that it is dependent on the DOM anymore, but only uses the model to determine whether there is a record to update]]
So back in the old days, we used that notification in the browser to refresh the (interactive) report. But along comes the Interactive Grid (IG). While he full-refresh mechanism still works for IG, an IG has also the option to refresh just one row.
So wouldn't it be awesome that just the changed row(s) get refreshed upon a change in the database, instead of the whole report? Can we do it ... yes we can!
First in our "Execute when Page Loads" property we start listening to the websocket server when the page is loaded using:
window.addEventListener("load", init, false);
In the "Function and Global Variable Declaration" we add the actual code and the init function:
//The websocket server is set using an Application Item
var wsUri = "&WSSERVER.";
function init() {
websocket = new WebSocket(wsUri);
websocket.onopen = function(evt) { onOpen(evt) };
websocket.onclose = function(evt) { onClose(evt) };
websocket.onmessage = function(evt) { onMessage(evt) };
websocket.onerror = function(evt) { onError(evt) };
}
// This is where the real magic happens
function onMessage(msg) {
// msg is in JSON format, containing the ROWID of the changed record
var rowid,
record,
records = [],
json = JSON.parse( msg.data ),
l = json.changes.length;
// "myGrid" is the Static ID of the IG region
var myGrid = apex.region("myGrid").widget().interactiveGrid("getViews").grid;
for ( var i = 0; i < l; i++){
rowid = json.changes[i].rowid ;
// loop through all the rows, check if the rowid is present
// forEach callback params : record, index, key
myGrid.model.forEach( function(r, i, k){
if ( $.inArray( rowid, r ) > -1 ) {
record = myGrid.model.getRecord(k);
if ( myGrid.model.getRecordMetadata(k).updated ){
apex.message.alert("Record " + (i+1) + " is changed by another user and is requeried");
}
records.push( record );
}
});
}// fetch the changed records
if ( records.length > 0 ) {
myGrid.model.fetchRecords(records);
}
}
// Addtional helper functions below
$(window).on("beforeunload", function(){
websocket.close();
});
function onOpen(evt) {
apex.debug("Websocket opened on &WSSERVER.");
}
function onClose(evt) {
apex.debug("Websocket closed");
}
function onError(evt) {
apex.debug("Websocket Error");
apex.debug(evt);
}
The key of the code above is that the records that are changed and are found on the current page are added to an array of records. And that array us used to fetch the records. If you inspect the network traffic that is going on, you can verify that only the changed records (in the screen shot below, three changed records) are fetched and shown on the screen.
The whole process works seamless for the user. If he made a change to a record that didn't get updated by someone else (or another process) than he can keep working on that, if he did make a change - and thus there is a conflict - he will get a notification. In our example the process didn't even show a progress spinner, but maybe that's because our queries are fast (it is not on EMP, but based on a view that references several tables and returns over 40,000 rows).
[Edit Jul 4 : I changed the code in a way that it is dependent on the DOM anymore, but only uses the model to determine whether there is a record to update]]
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