Dynamically build update parameters required for the DynamoDB Client. Just pass a JSON object of the fields you want to update and get the UpdateExpression, ExpressionAttributeNames and ExpressionAttributeValues returned.

buildUpdateParams.js

function mapToObject (processMap) {
  const returnObject = {}
  for (const [key, value] of processMap) {
    returnObject[key] = value
  }
  return returnObject
}

function randomString (stringLength) {
  const chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz'
  let randomstring = ''
  for (let i = 0; i < stringLength; i++) {
    const rnum = Math.floor(Math.random() * chars.length)
    randomstring += chars.substring(rnum, rnum + 1)
  }
  return randomstring
}

function buildUpdateExpression (item, parent, expressionMap, attributeNameObj) {
  for (const index in item) {
    if (typeof item[index] === 'object') {
      if (Array.isArray(item[index])) {
        const tempArray = item[index]
        // console.log(tempArray)
        const identifier = `#${randomString(4)}`
        // attributeNameObj[identifier] = index
        for (let i = 0; i < tempArray.length; i++) {
          const indexIdentifier = `${identifier}[${i}]`
          attributeNameObj[identifier] = index
          const key = parent
            ? `${parent}.${indexIdentifier}`
            : `${indexIdentifier}`
          if (typeof tempArray[i] === 'object') {
            buildUpdateExpression(
              tempArray[i],
              key,
              expressionMap,
              attributeNameObj
            )
          } else {
            expressionMap.set(key, tempArray[i])
          }
        }
      } else {
        const identifier = `#${randomString(4)}`
        attributeNameObj[identifier] = index
        const key = parent ? `${parent}.${identifier}` : identifier
        buildUpdateExpression(item[index], key, expressionMap, attributeNameObj)
      }
    } else {
      const identifier = `#${randomString(4)}`
      attributeNameObj[identifier] = index
      const key = parent ? `${parent}.${identifier}` : identifier
      expressionMap.set(key, item[index])
    }
  }
}

function buildUpdateParams (item) {
  const returnMap = new Map()
  const returnObj = {}

  buildUpdateExpression(item, null, returnMap, returnObj)

  let strUpdateExpression = 'SET'
  const mapExpressionAttributeValues = new Map()

  for (const [key, value] of returnMap.entries()) {
    const variableidentifier = randomString(5)
    strUpdateExpression += ` ${key} = :${variableidentifier},`
    mapExpressionAttributeValues.set(`:${variableidentifier}`, value)
  }

  return {
    UpdateExpression: strUpdateExpression.slice(
      0,
      strUpdateExpression.length - 1
    ),
    ExpressionAttributeNames: returnObj,
    ExpressionAttributeValues: mapToObject(mapExpressionAttributeValues)
  }
}

export default buildUpdateParams