如何查询一组 AWS-CLI (DynamoDB) 的大小？

Question

There is a column in the table whose data type is set of strings. I want to get the results based on the condition on the size of that set. How can I write the filter expression for it in AWS-CLI?

Answer 1

You can see a complete summary of condition expressions here . The feature you are looking for exists (assuming that by "size" of a set you mean the number of elements) - it is the size() function. Quoting the relevant part of that document:

If the attribute is a Set data type, size returns the number of elements in the set.

Example: Check whether the product is available in more than one color. The expression attribute value :v_sub is a placeholder for 1.

size (Color) <:v_sub

Please remember that although this sort of filtering can avoid sending you the non-matching items, you will still be paying full price for the read of these items, even if not returned. So if you need to do this often and to filter out a lot of items, you may want to reconsider your data model to help you more efficiently retrieve only the relevant items.