How to update multiple items in a DynamoDB table at once

I don't know if it has changed since the answer was given but it's possible now

See the docs: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_BatchWriteItem.html

I have used it like this in javascript (mapping the new blocks to an array of objects with the wanted structure:

let params = {}
let tableName = 'Blocks';

params.RequestItems[tableName] = _.map(newBlocks, block => {
    return {
        PutRequest: {
            Item: {
                'org_id': orgId,
                'block_id': block.block_id,
                'block_text': block.block_text
            },
            ConditionExpression: 'org_id <> :orgId AND block_id <> :block_id',
            ExpressionAttributeValues: {
                ':orgId': orgId,
                ':block_id': block.block_id
            }
        }
    }
})

docClient.batchWrite(params, function(err, data) {
   .... and do stuff with the result

You can even mix puts and deletes

And if your using dynogels (you cant mix em due to dynogels support but what you can do is for updating (use create because behind the scenes it casts to the batchWrite function as put's)

var item1 = {email: '[email protected]', name: 'Foo 1', age: 10};
var item2 = {email: '[email protected]', name: 'Foo 2', age: 20};
var item3 = {email: '[email protected]', name: 'Foo 3', age: 30};

Account.create([item1, item2, item3], function (err, acccounts) {
  console.log('created 3 accounts in DynamoDB', accounts);
});

Note this from DynamoDB limitations (from the docs):

The BatchWriteItem operation puts or deletes multiple items in one or more tables. A single call to BatchWriteItem can write up to 16 MB of data, which can comprise as many as 25 put or delete requests. Individual items to be written can be as large as 400 KB.

If i remember correctly i think dynogels is chunking the requests into chucks of 25 before sending them off and then collecting them in one promise and returns (though im not 100% certain on this) - otherwise a wrapper function would be pretty simple to assemble

As you noted, DynamoDB does not support a batch update operation. You would need to query for, and obtain the keys for all the records you want to update. Then loop through that list, updating each item one at a time.