Indexed DB cursor ranges on multiple properties

Question

I have a composite index of two properties on an indexeddb objectstore and wish to retrieve a cursor based on the range of both of these properties.

Here's an example object in the store :

{species: 'Oak',xcoord: 123456, ycoord: 654321}

and index :

treeStore.createIndex("treelocation", ["xcoord","ycoord"], { unique: false });

The index creation is succesful and I can see it in the Chrome developer tools, however now I'd like to open a cursor with a keyrange on both the x and y co-ordinates (which will be the extent of a map).

Searching online I can't see how to do this, and opening an index with an array of key ranges doesn't seem to work.

Answer 1

The range suggestion is part of the answer, but even with array keys it really is just a 1-dimensional range, not a 2- (or N-) dimensional selection of the data. With your current schema you'll need to do something like this:

index.openCursor([lowX, lowY], [highX, highY]).onsuccess = function(e) {
    var cursor = e.target.result;
    if (!cursor) return; // done!

    var x = cursor.key[0], y = cursor.key[1];
    // assert(lowX <= x && x <= highX);
    if (y < lowY) {
        cursor.continue([x, lowY]);
    } else if (y > highY) {
        cursor.continue([x + 1, lowY]);
    } else {
        processRecord(cursor.value); // we got one!
        cursor.continue();
    }
};

(if coordinates are not integral, replace + 1 with an appropriate epsilon)

I've posted an example of a generalized solution to:

https://gist.github.com/inexorabletash/704e9688f99ac12dd336