How to dynamically update an attribute in a dynamodb item?

Question

I created an item in dynamodb using Node js, the item has multiple attributes such as brand, category, discount, validity, etc. I am using uuid to generate ids for each item. Now let's say I want to update the validity attribute of the item, in which case I am currently sending the entire json object with the value of validity modified to the new value.

This is definitely not optimal, please help me find an optimal solution.

const params = {
    TableName: process.env.PRODUCT_TABLE,
    Key: {
      id: event.pathParameters.id,
    },
    ExpressionAttributeNames: {
      '#discount': 'discount',
    },
    ExpressionAttributeValues: {
      ':brand': data.brand,
      ':category': data.category,
      ':discount': data.discount,
      ':denominations': data.denominations,
      ":validity": data.validity,
      ":redemption": data.redemption    
    },
    UpdateExpression: 'SET #discount = :discount, denominations = :denominations, brand = :brand, category = :category, validity = :validity, redemption = :redemption',
    ReturnValues: 'ALL_NEW',
  };

I want to send just the attribute I want to update with the new value, if I want to change the validity from 6 months to 8 months, I should just send something like: { "validity": "8 months" } And it should update the validity attribute of the item. Same should apply to any other attribute of the item.

'use strict';

const AWS = require('aws-sdk');

const dynamoDb = new AWS.DynamoDB.DocumentClient();

module.exports.update = (event, context, callback) => {
  const data = JSON.parse(event.body);

  let attr = {};
  let nameobj = {};
  let exp = 'SET #';
  let arr = Object.keys(data);
  let attrname = {};

  arr.map((key) => {attr[`:${key}`]=data[key]});

  arr.map((key) => {
    exp += `${key} = :${key}, `
  });

  arr.map((key) => {nameobj[`#${key}`]=data[key]});

  attrname = {
    [Object.keys(nameobj)[0]] : nameobj[Object.keys(nameobj)[0]]
  }

  const params = {
    TableName: process.env.PRODUCT_TABLE,
    Key: {
      id: event.pathParameters.id,
    },
    ExpressionAttributeNames: attrname,
    ExpressionAttributeValues: attr,
    UpdateExpression: exp,
    ReturnValues: 'ALL_NEW',
  };

  // update the todo in the database
  dynamoDb.update(params, (error, result) => {
    // handle potential errors
    if (error) {
      console.error(error);
      callback(null, {
        statusCode: error.statusCode || 501,
        headers: { 'Content-Type': 'text/plain' },
        body: 'Couldn\'t update the card',
      });
      return;
    }

    // create a response
    const response = {
      statusCode: 200,
      body: JSON.stringify(result.Attributes),
    };
    callback(null, response);
  });
};

Answer 1

Contrary to others comments, this is very possible, use the UpdateItem action.

Language agnostic API docs

JavaScript specific API docs

If you want to dynamically create the query, try something like this:

const generateUpdateQuery = (fields) => {
    let exp = {
        UpdateExpression: 'set',
        ExpressionAttributeNames: {},
        ExpressionAttributeValues: {}
    }
    Object.entries(fields).forEach(([key, item]) => {
        exp.UpdateExpression += ` #${key} = :${key},`;
        exp.ExpressionAttributeNames[`#${key}`] = key;
        exp.ExpressionAttributeValues[`:${key}`] = item
    })
    exp.UpdateExpression = exp.UpdateExpression.slice(0, -1);
    return exp
}

let data = {
    'field' : { 'subfield': 123 },
    'other': '456'
}

let expression = generateUpdateQuery(data)

let params = {
    // Key, Table, etc..
    ...expression
}

console.log(params)

Output:

{ 
    UpdateExpression: 'set #field = :field, #other = :other',
    ExpressionAttributeNames: {
        '#field': 'field',
        '#other': 'other'
    },
    ExpressionAttributeValues: {
        ':field': { 
            'subfield': 123
        },
        ':other': '456'
    } 
}