How to dynamically update an attribute in a dynamodb item? - amazon-dynamodb

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'
}
}

Answer 2

Using Javascript SDK V3:
Import from the right package:
import { DynamoDBClient PutItemCommandInput, UpdateItemCommandInput, UpdateItemCommand } from '#aws-sdk/client-dynamodb';
Function to dynamically do partial updates to the item:
(the code below is typescript can be easily converted to Javascript, just remove the types!)
function updateItem(id: string, item: any) {
const dbClient = new DynamoDBClient({region: 'your-region-here });
let exp = 'set ';
let attNames: any = { };
let attVal: any = { };
for(const attribute in item) {
const valKey = `:${attribute}`;
attNames[`#${attribute}`] = attribute;
exp += `#${attribute} = ${valKey}, `;
const val = item[attribute];
attVal[valKey] = { [getDynamoType(val)]: val };
}
exp = exp.substring(0, exp.length - 2);
const params: UpdateItemCommandInput = {
TableName: 'your-table-name-here',
Key: { id: { S: id } },
UpdateExpression: exp,
ExpressionAttributeValues: attVal,
ExpressionAttributeNames: attNames,
ReturnValues: 'ALL_NEW',
};
try {
console.debug('writing to db: ', params);
const command = new UpdateItemCommand(params);
const res = await dbClient.send(command);
console.debug('db res: ', res);
return true;
} catch (err) {
console.error('error writing to dynamoDB: ', err);
return false;
}
}
And to use it (we can do partial updates as well):
updateItem('some-unique-id', { name: 'some-attributes' });

Answer 3

What i did is create a helper class.
Here is a simple function : Add all the attribute and values that goes into, if the value is null or undefined it won't be in the expression.
I recommande to create a helper class with typescript and add more functions and other stuff like generator of expressionAttributeValues , expressionAttributeNames ... , Hope this help.
function updateExpression(attributes, values) {
const expression = attributes.reduce((res, attribute, index) => {
if (values[index]) {
res += ` #${attribute}=:${attribute},`;
}
return res;
}, "SET ");
return expression.slice(0, expression.length - 1)
}
console.log(
updateExpression(["id", "age", "power"], ["e8a8da9a-fab0-55ba-bae3-6392e1ebf624", 28, undefined])
);

Answer 4

You can use code and generate the params object based on the object you provide. It's just a JavaScript object, you walk through the items so that the update expression only contains the fields you have provided.
This is not really a DynamoDB question in that this is more a general JS coding question.

Answer 5

You can use UpdateItem; to familiarize yourself with DynamoDb queries I would suggest you DynamoDb NoSQL workbench:
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/workbench.settingup.html
It can generate snippets for you based on your queries.
DynamoDb NoSQL workbench screenshot query