Question

I’ve created a set of JSON data that gets passed into IndexedDB during the upgrade event. It creates a very nice IndexedDB database with seemingly no problems. The problem is when you upgrade the database from version 1 to 2 it overwrites all existing data since it just loops through the JSON and applies it.

There must be some way in the upgrade to prevent a new database item that doesn’t have a unique key from writing anything. How would I do this? As the following just overwrites current data.

objectStore = event.currentTarget.transaction.objectStore('player');
objectStore.put({ key: 'non unique, but I replace my twin\'s data anyway', data: value });

Thanks in advance for the help, searched everything and can’t find a solution to this problem.

EDIT 8/24/2012

As per Kristof’s recommendation of using get to check information, I did a bit of digging and research. After finding the answer I decided to write some psuedo code to help you out.

// Create the get request inside your upgrade
var tableData = event.currentTarget.transaction.objectStore('your table name');
var getData = tableStore.get('your key');

// Run the get request
getData.onsuccess = function (e) {
    var result = e.target.result;

    // Immediately exit if the current result is not undefined
    if (result !== undefined) {
        return;
    }

    // Note, you may or may not need a closure to write data in the callback
    // See here for more info on closures in events http://stackoverflow.com/questions/3495679/passing-parameters-in-javascript-onclick-event#answer-3495722
    tableStore.add('data to add');
};

Answer 1

Overwriting of data can only happen if it finds a key that already exist in the database. If it doesn’t find the key, it will be just added.

If you want to prevent that this data gets inserted for a second time or update there are some solutions:

• Before putting the data, check if anything wit that key exists (get method)
• Use the add method instead of the put. (this will result in an error when a key already exists. Not very nice)
• Check if the old version of the database is 0 or nothing and only then run the insert.