How to filter list value in DynamoDB

Question

I am currently new to AWS DynamoDB and noSql. I am lost here on filtering list value in DynamoDB.

Let's say that I have 2 items in this table.

[
  {
    "id": 1,
    "title": "Robots in Music"
    "topics": ["Robots", "Violin"]
  },
  {
    "id": 2,
    "title": "Where are good places to see stars"
    "topics": ["Robots", "Stars"]
  },
]

I want to filter using topics column.

ex.

1. User wants to get the item with topics having "Robots".

2. User gets item with id 1 and 2

3. User wants to get item with topics having "Stars".

4. Then user gets item with id 2.

I tried to search internet and found that I can use 'QueryFilter' 'contains'. However, I know that 'contains' is scanning all the table and for DynamoDB they can extract 1MB of data in single query. Which means the action needs to be repeated and it would cost way more than using single index.

Is there any way to use GSI and filter the list effectively?

Answer 1

Unfortunately you cannot index a list type or any other type of nested attrubute, and your use case would require you to Scan the entire table to know which users contained a particular topic.

1. Would require a Scan
2. A GetItem if the user wants just id1 or of the user wants both id1 and id2 then a BatchGetItem
3. Same as 1
4. GetItem

Of your use-case requires searching nested attributes then you can consider using a relational database or something more flexible like OpenSearch.