Prompt Title: React Native Lambda Function.

To ensure that related items in the "PostLike" and "PostComment" tables are deleted when an item is deleted from the "Post" table in DynamoDB, you can create a Lambda function that will be triggered by a DynamoDB stream associated with the "Post" table.

Here are the high-level steps to achieve this:

1. Create a Lambda function in AWS that will be triggered by a DynamoDB stream. This function will contain the logic to delete related items from the "PostLike" and "PostComment" tables when an item is deleted from the "Post" table.

2. Configure a DynamoDB stream for the "Post" table. This stream will capture all changes made to the "Post" table, including deletions.

3. Add the necessary permissions to the Lambda function to allow it to access the "PostLike" and "PostComment" tables in DynamoDB.

4. In the Lambda function, use the DynamoDB stream event to determine which item was deleted from the "Post" table. You can do this by checking the "eventName" property of the stream event to see if it is set to "REMOVE".

5. Once you have identified the deleted item, use the "post_id" (or any other unique identifier) to delete related items from the "PostLike" and "PostComment" tables. You can use the "batchWrite" function of the AWS SDK for DynamoDB to delete multiple items in a single request.

Here's some sample code that demonstrates how you can implement this logic in your Lambda function:

csharpCopy code
const AWS = require('aws-sdk');
const dynamoDb = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  for (const record of event.Records) {
    if (record.eventName === 'REMOVE') {
      const post_id = record.dynamodb.Keys.post_id.S;
      
      // Delete related items from PostLike table
      const postLikeParams = {
        RequestItems: {
          'PostLike': {
            Keys: [{ post_id }]
          }
        }
      };
      await dynamoDb.batchWrite(postLikeParams).promise();
      
      // Delete related items from PostComment table
      const postCommentParams = {
        RequestItems: {
          'PostComment': {
            Keys: [{ post_id }]
          }
        }
      };
      await dynamoDb.batchWrite(postCommentParams).promise();
    }
  }
};

Note: This is just a basic example to get you started. You may need to modify this code to fit your specific requirements.

If you delete an item from the "Post" table and trigger a Lambda function that calls batchWrite to delete related items from the "PostLike" and "PostComment" tables, it will not trigger the Lambda functions associated with those tables.

This is because the Lambda functions associated with the "PostLike" and "PostComment" tables are triggered by changes to those tables, not changes to the "Post" table.

In other words, if you want the Lambda functions associated with the "PostLike" and "PostComment" tables to be triggered when an item is deleted from the "Post" table, you need to modify your architecture to include a DynamoDB stream on the "Post" table that triggers a Lambda function. That Lambda function can then call batchWrite to delete related items from the "PostLike" and "PostComment" tables.

Alternatively, you can modify the Lambda functions associated with the "PostLike" and "PostComment" tables to check for the presence of related items in the "Post" table before processing the event. If the related item has been deleted from the "Post" table, the Lambda functions can skip processing the event for that item. However, this approach may result in unnecessary processing and may not be the most efficient solution.

Yes, batchWrite can delete multiple items from a DynamoDB table in a single request. The maximum number of items that can be deleted in a single batchWrite request is 25. However, you can send multiple batchWrite requests in parallel to delete larger numbers of items.

In your case, if you have over 1000 items related to a "Post" item that you want to delete, you can use a loop in your Lambda function to send multiple batchWrite requests to delete the related items in batches of 25.

Here's an example code snippet that demonstrates how you can do this:

phpCopy code
const AWS = require('aws-sdk');
const dynamoDb = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  for (const record of event.Records) {
    if (record.eventName === 'REMOVE') {
      const post_id = record.dynamodb.Keys.post_id.S;

      // Delete related items from PostLike table
      const postLikeParams = {
        RequestItems: {
          'PostLike': []
        }
      };

      // Add up to 25 items to the batch request
      const postLikeItems = await dynamoDb.query({
        TableName: 'PostLike',
        IndexName: 'post_id-index',
        KeyConditionExpression: 'post_id = :post_id',
        ExpressionAttributeValues: { ':post_id': post_id }
      }).promise();

      postLikeItems.Items.forEach(item => {
        postLikeParams.RequestItems['PostLike'].push({
          DeleteRequest: {
            Key: { post_id: item.post_id, like_id: item.like_id }
          }
        });
      });

      // Send the batch request to delete the related items from PostLike table
      await dynamoDb.batchWrite(postLikeParams).promise();

      // Delete related items from PostComment table
      const postCommentParams = {
        RequestItems: {
          'PostComment': []
        }
      };

      // Add up to 25 items to the batch request
      const postCommentItems = await dynamoDb.query({
        TableName: 'PostComment',
        IndexName: 'post_id-index',
        KeyConditionExpression: 'post_id = :post_id',
        ExpressionAttributeValues: { ':post_id': post_id }
      }).promise();

      postCommentItems.Items.forEach(item => {
        postCommentParams.RequestItems['PostComment'].push({
          DeleteRequest: {
            Key: { post_id: item.post_id, comment_id: item.comment_id }
          }
        });
      });

      // Send the batch request to delete the related items from PostComment table
      await dynamoDb.batchWrite(postCommentParams).promise();
    }
  }
};

Note that in this example, we're using the query operation to fetch related items from the "PostLike" and "PostComment" tables using an index on the "post_id" attribute. You may need to adjust the query parameters based on the structure of your tables and indexes.

If you need to delete more than 25 items in a single request, you can use the delete operation instead of batchWrite.

The delete operation allows you to delete a single item or a batch of items from a DynamoDB table in a single request, with a maximum of 25 items per request. However, unlike batchWrite, the delete operation is not designed for bulk delete operations and may not be as efficient for large-scale deletes.

Here's an example code snippet that demonstrates how you can use the delete operation to delete multiple items from a DynamoDB table:

phpCopy code
const AWS = require('aws-sdk');
const dynamoDb = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  for (const record of event.Records) {
    if (record.eventName === 'REMOVE') {
      const post_id = record.dynamodb.Keys.post_id.S;

      // Delete related items from PostLike table
      const postLikeItems = await dynamoDb.query({
        TableName: 'PostLike',
        IndexName: 'post_id-index',
        KeyConditionExpression: 'post_id = :post_id',
        ExpressionAttributeValues: { ':post_id': post_id }
      }).promise();

      const postLikeKeys = postLikeItems.Items.map(item => {
        return { post_id: item.post_id, like_id: item.like_id };
      });

      // Delete the related items from PostLike table in batches of 25
      while (postLikeKeys.length > 0) {
        const batchKeys = postLikeKeys.splice(0, 25);

        const postLikeParams = {
          RequestItems: {
            'PostLike': batchKeys.map(key => {
              return { DeleteRequest: { Key: key } };
            })
          }
        };

        await dynamoDb.batchWrite(postLikeParams).promise();
      }

      // Delete related items from PostComment table
      const postCommentItems = await dynamoDb.query({
        TableName: 'PostComment',
        IndexName: 'post_id-index',
        KeyConditionExpression: 'post_id = :post_id',
        ExpressionAttributeValues: { ':post_id': post_id }
      }).promise();

      const postCommentKeys = postCommentItems.Items.map(item => {
        return { post_id: item.post_id, comment_id: item.comment_id };
      });

      // Delete the related items from PostComment table in batches of 25
      while (postCommentKeys.length > 0) {
        const batchKeys = postCommentKeys.splice(0, 25);

        const postCommentParams = {
          RequestItems: {
            'PostComment': batchKeys.map(key => {
              return { DeleteRequest: { Key: key } };
            })
          }
        };

        await dynamoDb.batchWrite(postCommentParams).promise();
      }
    }
  }
};

In this example, we're using the query operation to fetch related items from the "PostLike" and "PostComment" tables using an index on the "post_id" attribute. We're then using a loop to delete the related items in batches of 25 using the batchWrite operation.

Note that using delete to delete large numbers of items may result in high read capacity units (RCUs) and write capacity units (WCUs) consumption, which can lead to increased costs and potential performance issues. Therefore, it's important to consider the impact of large-scale deletes on your DynamoDB capacity and performance before implementing this approach.