check if a value exists in dynamodb table using python and fetch that record

Question

I am new to Dynamodb and learning currently. I am using python to query dynamodb to get some records based on a IF condition.

I have a dynamodb table cus_token, has only two attributes a) customerId and b) token

When a user provides token, check if that token exists in the cus_token table, and if it exists I want to query out and fetch the customerID for that token. I tried to to do it this way

Suppose user_input = "Rooxp9" (this is a token in the cus_token table)

first get all the values with token attribute

import boto3
import json

def gettokens(y):
    dynamodb = boto3.resource('dynamodb')
    table = dynamodb.Table('cus_token')
    response = table.scan()

    tokens = []
    for i in response['Items']:
        nameList.append(i['token'])

    return tokens

temp = gettokens(cus_token)

Check using IF condition

for item in temp:
    if item == user_input:
        "Here I want to write the code to fetch the customerID"

Seth Geoghegan · Accepted Answer · 2020-09-01 02:13:16Z

1

It sounds like you'd like to fetch a customerID given a token.

To do this with your current table design, you'd want to use a Filter Expression to ask DynamoDB to return all attributes where the token is equal to the user input. For example, here's a snippet in pseudocode:

response = table.scan({"FilterExpression": "#token = :token",
                       "ExpressionAttributeNames": {"#token":"token"},
                       "ExpressionAttributeValues": {":token": {"S": <user_input>}})

There's no need to scan the entire database, return it to your application, then filter the results in your application.

If you are just getting started with DynamoDB, I'd highly recommend The DynamoDB Guide website. It does a great job explaining DynamoDB to beginners.

answered Sep 1, 2020 at 2:13

Seth Geoghegan

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2 Comments

ashakshan Over a year ago

I also want to validate whether user given token matches with the token existing the in table. Only If the token matches, I need to fetch the corresponding customerID

Seth Geoghegan Over a year ago

This scan operation will only return items where the token matches what you ask for (the user input). If there is no match, you will get no results. There is no need for additional validation. By default, the scan operation will return all attributes in the matching items, meaning you will have the CustomerID in your results.

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