Indexeddb : How to limit number of objects returned?

Question

I'm using a cursor with a lower bound range query. I can't find a way to limit the number of objects returned, similar to a "LIMIT n" clause in a databse.

var keyRange = IDBKeyRange.lowerBound('');

Does it not exist ?

Answer 1

As you're iterating through the results, you can stop at any time. Something like this should work:

var results = [];
var limit = 20;
var i = 0;

objectStore.openCursor().onsuccess = function (event) {
  var cursor = event.target.result;
  if (cursor && i < limit) {
    results.push(cursor.value);
    i += 1;
    cursor.continue();
  }
  else {
    // Do something with results, which has at most 20 entries
    console.log(results);
  }
};

Also, in the special case where you are selecting based on a key that is made up of sequential numbers, you could use a keyRange to explicitly return only a certain range. But that's generally not the case.

Answer 2

An important fix its replace:

if (cursor && i < limit) {

for

if (cursor && results.length < limit) {

Remember that its an async call, and it could be adding elements on "results" at the same time and "i" would not have the proper value.