Jelly Fin: Should I use a query or scan?

sublimegeek profile image Jonathan Irvin ・1 min read

Hey Dev.to,

I have an endpoint where I'm trying to get a subset of transactions by date using between. When I run this, I get no results. Odd thing is, I get no errors either.

I know, I know...why not post this on StackOverflow. I don't feel like being judged and you guys are much more supportive. :)

// get transactions for {month} and {year}
api.get('/transaction/tab/{year}/{month}', (request) => {
  const year = request.pathParams.year
  const month = request.pathParams.month
  const params = {
    TableName: request.env.tableName,
    KeyConditionExpression: '#date between :val1 and :val2',
    ExpressionAttributeNames: {
      '#date': 'date'
    ExpressionAttributeValues: {
      ':d': 'date',
      ':val1': year +'-'+month+'-01',
      ':val2': year +'-'+month+'-'+getDaysInMonth(month, year)


  // post-process dynamo result before returning
  dynamoDb.query(params, (err, data) => {
    if (err) {
      console.error('Unable to query. Error:', JSON.stringify(err, null, 2))
      return 'Unable to query. Error: '+ JSON.stringify(err, null, 2)
    } else {
      console.log('Query succeeded.')
      data.Items.forEach((item) => {
        console.log(' -', item.year + ': ' + item.title)
      return data.Items

Here's my data model:

    id: String
    date: String

Posted on Aug 1 '18 by:

sublimegeek profile

Jonathan Irvin


I'm a full-stack cloud-minded engineer who enjoys devops and clean code.


markdown guide

I think the problem is here:

ExpressionAttributeValues: {
  ':d': 'date',
  ':val1': year +'-'+month+'-01',
  ':val2': year +'-'+month+'-'+getDaysInMonth(month, year)

If you see the docs you can figure out how you need write the correct values for ExpressionAttributeValues, something like that maybe:

ExpressionAttributeValues: {
  ':val1': {
    'S': year +'-' + month + '-01'
  ':val2': {
    'S': year + '-' + month + getDaysInMonth(month, year)

':d': 'date' isn't necessary...


@kip13 thank you! I'm going to try that out now. Date is a restricted word in AWS. Restricted Words. Lame? Right?


Tried that and we're still not getting results. I'm storing dates as strings and "2018-01-01" as an example. Should I just start storing dates as timestamps?


Isn't neccesary, you can use Strings

Can you try with FilterExpression ?


If date isn't an index or sort key you need to use FilterExpression see


Not quite yet. I just made the source public, if you want to check it out.

jonathan-irvin / jelly-fin

A simple way to manage your finances with forecasting. We should automate our money, not make it automate us.

Jelly Fin

Finances are hard. It's one of the first adulting things everyone has to wrestle with. So, let's make it easy and automate it. Over the course of several years, my wife and I have tracked our finances using a forecasting method and had done it all within a spreadsheet. The time came where I wanted to take this concept and make it mobile using serverless architecture and clean design.

The idea is to take what we know: the transactions that are predictable like mortgage and insurance and just keep track of them against the account balance. Then take transactions that aren't predictable and try to predict them using seasonality analytics. Does your electric bill go up in the summer? Let's predict what it would be and try and account for it.


@kip13 I think for my head I may use timestamps for the date. The math just works better that way.