DynamoDB - Dynamically Map-Reduce a Batch Update Request in to Blocks of 25 Items

put-batch.js

// Your DocClient ...

function SplitBatch(params) {
    const max_items = 25;
    let tables = Object.entries(params.RequestItems);
    let transactions = {};

    for (const [table, requests] of tables) {
        for (let index = 0; index < requests.length; index += max_items) {
            let block = requests.slice(index, index + max_items);
            if (!transactions[table]) {
                transactions[table] = [block]
            } else {
                let last = transactions[table][transactions[table].length - 1];
                let idx = last.length;

                if(idx < max_items){
                    let first = block.slice(0, idx);
                    let second = block.slice(idx);
                    last.splice(idx, 0, ...first);
                    transactions[table].push(second)
                } else {
                    transactions[table].push(block)
                }
            }
        }
    }

    let reduced = Object.entries(transactions)
    .reduce((acc, [table, requests]) => {
        for (const req of requests){
            acc.push({
                RequestItems: {
                    [table]: req
                }
            });
        }
        return acc;
    }, [])

    return reduced;
}


async function PutBatch(items) {
    var params = {
        RequestItems: {
            'tablename': items.map(item => ({
                PutRequest: {
                    Item: item
                }
            }))
        }
    };

    let requests = SplitBatch(params);

    let unprocessed = []

    for (const req of requests) {
        await DocClient.batchWrite(req).promise()
            .then(
                item => unprocessed.splice(unprocessed.length, item['UnprocessedItems']),
                err => console.log(err, params)
            );
    }

    return unprocessed;
}