Create deleting function

In this section, we will create a function to delete document information stored in the DynamoDB table by user id and filename.

1. Open AWS Lambda console

2. Click Create function

3. Enter function name: delete_documents

• Select Python 3.11 for Runtime
• Click Create function

4. Enter the following code for the lambda_function.py file:

import json
import boto3
import os

client = boto3.resource('dynamodb')

def lambda_handler(event, context):
    # TODO implement
    table_name = os.environ['TABLE_NAME']
    error = None
    doc_pk = event['pathParameters']['id']
    print("doc_pk ", doc_pk)
    doc_sk = event['queryStringParameters']['file']
    print("doc_sk ", doc_sk)
    table = client.Table(table_name)
    key = {
        'user_id':doc_pk,
        'file':  doc_sk
    }
    
    try:
        table.delete_item(Key = key)
    except Exception as e:
        error = e
        
        
    except Exception as e:
        error = e
        
    if error is None:
        message = 'delete document successful!'
    else:
        print(error)
        message = 'delete document fail'
    
    return {
            'statusCode': 200,
            'body': message,
            'headers': {
                'Content-Type': 'application/json',
                'Access-Control-Allow-Origin': '*'
            },
        }

• Then click Deploy

The above code executes to get the TABLE_NAME environment variable, partition key and sort key in request. Then execute the delete command to delete the item in the table with those partition key and sort key.

5. We need to add an environment variable to the function. Click the Configuration tab, then select Environment variables in the left menu. Press Edit

6. Click Add environment variable

• Enter TABLE_NAME as key
• Enter the DynamoDB table name that you just created
• Click Save

7. Next, add permissions for function to access DynamoDB table

• Click Permission on the left menu
• Click on the execution role of the function

8. Expand the AWSLambdaBasicExecutionRole… policy, then click Edit

9. Copy the JSON below into the editor

,
        {
            "Effect": "Allow",
            "Action": [
                "dynamodb:DeleteItem"
            ],
            "Resource": "arn:aws:dynamodb:REGION:ACCOUNT_ID:table/Documents"
        }

Replace REGION and ACCOUNT_ID with the region you create the table and your account id.

• Click Review policy

10. Click Save changes