Indexed DB - HTML5 with Visual Studio 2012 - page 267

These calls will all be made using the same transaction. As I demonstrated at the beginning of the chapter,
you'll need to nest the onsuccess event handlers for each of these calls. Add the makeNextMove() function shown
in Listing 11-9 to the end of the script element.

Listing 11-9. Implementing the makeNextMove() function

function makeNextMove() {

var xact = db.transaction(["move", "piece"], "readwrite");
var moveStore = xact.objectStore("move");

moveStore.get(moveNumber).onsuccess = function (e1) {
var startPos = e1.target.result.start;
var endPos = e1.target.result.end;
var startKey = null;
var oStart = null;

var pieceStore = xact.objectStore("piece");
var index = pieceStore.index("piecePosition");

index.getKey(startPos).onsuccess = function (e2) {
startKey = e2.target.result;

index.get(startPos).onsuccess = function (e3) {
oStart = e3.target.result;

// If there is a piece at the ending location, we'll
// need to update it to prevent a duplicate pos index
removePiece(endPos, oStart, startKey, pieceStore);
}
}
}
}

This function creates a transaction that will access both the move and piece store. The mode is set to
“readwrite” because the objects in the piece store will be modified. It then gets the move store and calls its get()
method specifying the current move, which is the key to the table. This will return a single object and the start
and end positions are extracted from the result in the onsuccess event handler.

■ Notice that this code doesn't explicitly define a request variable. Instead the onsuccess event handler is
attached directly to the database call. In the previous examples I declared a request variable and then attached the
event handler to it to help you see what was happening. However, attaching the event handler directly to the method
accomplishes the same thing but simplifies the code a little.

Tip