来自多个键的 Dynamodb 查询

Question

I'm relatively new to dynamodb, i'm trying to create a social media app using was dynamodb. I have a user followers table that looks like the below schema.

And this is how my posts table look like

Posts API

I am seeking a method to retrieve all posts created by followers of a specific user from the DynamoDB database. My initial plan was to first query the followers table to obtain a list of user IDs for the followers and then use those keys to query the posts table. However, I have been unable to determine a way to effectively query a table with a list of keys using DynamoDB. Additionally, I require the retrieved posts to be sorted by date and the querying process to support pagination through the use of LastEvaluatedKey, ExclusiveStartKey, and PageCount. Is it possible to accomplish this efficiently and with good performance using DynamoDB, or should I consider revising my data model?

(I am using nodejs)

Answer 1

How to create a schema for DynamoDB

1. Define your access patterns, list them out in order of priority
2. View other models/schemas which are similar online
3. Use a tool like NoSQL Workbench to create sample models with the ability to visualize
4. Iterate continuously, make necessary changes to the schema when you spot something that will make your schema more efficient/performant.

Your Schema

You have given a single access pattern:

I am seeking a method to retrieve all posts created by followers of a specific user from the DynamoDB database

Users

pk	sk	followers
user1	USER#user1	[user2, user4, user99]
user2	USER#user2	[user6, user4, user99]

Posts

pk	sk	post
user2	COMMENT#00001#DATE	some comment
user2	COMMENT#00002#DATE	some comment
user2	COMMENT#00003#DATE	some comment
user2	REPLY#00001#DATE	some reply
user2	POST#00001#DATE	some post
user2	POST#00002#DATE	some post
user99	COMMENT#00001#DATE	some comment
user99	COMMENT#00002#DATE	some comment
user99	COMMENT#00003#DATE	some comment
user99	REPLY#00001#DATE	some reply

Your access pattern

• GetItem for user user1
• Parse list of followers
• Run a Query for each userId returned from above and state that sk begins_with POST
• You will be returned each users post in order by date

Pseudo

SELECT followers FROM Users WHERE pk = 'user1' AND sk='USER#user1'

FOR user in followers:
    SELECT * FROM POSTS WHERE pk = user AND sk BEGINS_WITH 'POST'

Single Table Design

You could model both tables in a single table, but it doesn't provide much benefits other than having a single table to manage:

pk	sk	post	followers
user1	USER#user1		[user2, user4, user99]
user2	COMMENT#00001#DATE	some comment
user2	COMMENT#00002#DATE	some comment
user2	COMMENT#00003#DATE	some comment
user2	REPLY#00001#DATE	some reply

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Summary

I don't particularly like this format, if it were my application I would model it something similar to the DynamoDB Forum Example .