Error: DynamoDB scan filter expression not working

Rafal Wilinski

Answered by Rafal Wilinski

What's Causing This Error

The Scan operation in DynamoDB allows you to filter the results based on specific conditions using a filter expression. Still, if the filter expression is not working, it could be due to several reasons, such as:

  • The filter expression is not formatted correctly: The filter expression must be in the correct format. Otherwise, it will not work. The filter expression uses placeholders such as :val, :val1, :val2, etc., to represent the values you want to compare, and it uses the comparison operators such as =, <>, <, >, <=, >=, BETWEEN, IN, LIKE, NOT_NULL, NULL, CONTAINS, NOT_CONTAINS, BEGINS_WITH, attribute_type.
  • The filter is not applied to the correct attribute: The filter must be applied to the correct attribute in the table, otherwise, it will not return the expected results.
  • The attribute on which the filter is applied is not indexed: If the attribute on which the filter is applied is not indexed, DynamoDB will have to scan the entire table, which can be slow.
  • The type of attribute is not matching the filter's value: The attribute type and filter value must match, otherwise, it will not return the expected results.
  • Conditionals are not used correctly- AND and OR conditions are used to filter the results. If they are not used correctly, they could give unexpected results.

Solution: Here's How To Resolve It

Here are a few ways to solve this issue:

  • Verify the filter expression format: Make sure the filter expression is in the correct format and uses the correct placeholders and comparison operators.
  • Verify the attribute name- Make sure the filter is applied to the correct attribute in the table.
  • Use an indexed attribute- If possible, use an indexed attribute for filtering. It will significantly improve the performance.
  • Verify the attribute type- Make sure that the attribute type and filter value match.
  • Test your filter expression- Try to test your expression using the AWS CLI or the AWS SDKs to see the results.
  • Monitor the scan- Monitor the scan operation. Use CloudWatch or other monitoring tools to see if there are any errors or issues.
  • Use AND and OR correctly- make sure you use AND and OR correctly in your filter expression.

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