DynamoDB boto3 : How to query if a key has some value - amazon-dynamodb

Question

I'm writing a python code to query a table on dynamo DB. Along with other conditions I'd also like to get rows where there exists some value for the key I'm specifying.
KeyConditionExpression = Key('Status').eq('Done') & Key('Name').begins_with('A') & Key('Error').exists()
In the code above, I'd like to display rows where the column "Error" has some value be it anything.
but the last condition is throwing an error.
AttributeError: 'Key' object has no attribute 'exists'.
How can modify the code to incorporate the third query?

Answer 1

Assuming that your “Error” key is neither your partition key and nor sort key as you must specify the partition key name and value as an equality condition always. Also, for the sort key you can use one of the undermentioned comparison operators.
a = b — true if the attribute a is equal to the value b
a < b — true if a is less than b
a <= b — true if a is less than or equal to b
a > b — true if a is greater than b
a >= b — true if a is greater than or equal to b
a BETWEEN b AND c — true if a is greater than or equal to b, and less than or equal to c.
begins_with (a, substr)— true if the value of attribute a begins with a particular substring.
Now coming back to your issue, if you are using Query operation, then you can definitely use QueryFilter to check if some non-null value exists for key “Error”. The official documentation defines QueryFilter as :
In a Query operation, QueryFilter is a condition that evaluates the query results after the items are read and returns only the desired values.
The following comparison operators are available for QueryFilter:
EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN
Please refer to the undermentioned link to get more idea about the QueryFilter and FilterExpression
AWS Official Documentation Link : https://docs.amazonaws.cn/en_us/amazondynamodb/latest/developerguide/LegacyConditionalParameters.QueryFilter.html