Error: DynamoDB scan filter expression not working

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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