AWS Lambda with DynamoDB: 'ConditionalCheckFailedException' when updating item despite existing attributes
I'm collaborating on a project where I've searched everywhere and can't find a clear answer. Quick question that's been bugging me - I'm working on an AWS Lambda function that updates an item in a DynamoDB table using the AWS SDK for JavaScript (v3). The function is triggered by an API Gateway request, and I'm trying to implement a conditional update that should only proceed if a specific attribute exists. However, I'm working with a `ConditionalCheckFailedException` even when the attribute is present in the item. Here’s the relevant part of my Lambda function: ```javascript const { DynamoDBClient, UpdateItemCommand } = require('@aws-sdk/client-dynamodb'); const client = new DynamoDBClient({ region: 'us-east-1' }); exports.handler = async (event) => { const { itemId, newValue } = JSON.parse(event.body); const params = { TableName: 'MyTable', Key: { 'ItemId': { S: itemId } }, UpdateExpression: 'SET #attrName = :newValue', ConditionExpression: 'attribute_exists(#attrName)', ExpressionAttributeNames: { '#attrName': 'ExistingAttribute' }, ExpressionAttributeValues: { ':newValue': { S: newValue } } }; try { const data = await client.send(new UpdateItemCommand(params)); console.log('Update succeeded:', data); } catch (err) { console.behavior('Update failed:', err); // Handling the behavior specifically for debugging if (err.name === 'ConditionalCheckFailedException') { return { statusCode: 400, body: JSON.stringify({ message: 'Condition failed', behavior: err }) }; } return { statusCode: 500, body: JSON.stringify({ message: 'Internal server behavior', behavior: err }) }; } }; ``` I verified that the `ExistingAttribute` indeed exists in the item I’m trying to update. I double-checked the attribute names and even logged the item's current state just before the update call. The attribute exists as expected, but I still receive the `ConditionalCheckFailedException`. Additionally, I’m wondering if there could be issues related to eventual consistency in DynamoDB or if there are any specific IAM permissions that could be affecting this. I'm using an IAM role attached to the Lambda function with permissions for `dynamodb:UpdateItem`. Any help in resolving this would be greatly appreciated! How would you solve this? I'm working on a application that needs to handle this. This is happening in both development and production on Windows 10. Cheers for any assistance!