Trial #25: Invalid DynamoDB KeyConditionExpression “ValidationException”

Problem:

If you attempt to use the DynamoDB KeyConditionExpression like you might a SQL query, and chain on several clauses with the and keyword, you may experience one of the two following error messages in the a Amazon.DynamoDBv2.AmazonDynamoDBException "ValidationException"

• "Conditions can be of length 1 or 2 only"
• "Query condition missed key schema element"

This is because the KeyConditionExpression is exclusively for querying the elements that combine to make the primary key. That is the Partiton Key and the optional Sort Key. Furthermore you may use only the Partiton Key but you may not use the Sort Key without the Partiton Key.

The following will all produce exceptions:

KeyConditionExpression = "SortKey = :v_VALUE"
...
KeyConditionExpression = 
    "PartitonKey = :v_VALUE1 and OtherKey = :v_VALUE2"
...
KeyConditionExpression = 
    "PartitonKey = :v_VALUE1 and SortKey = :v_VALUE2 and OtherKey = :v_VALUE3"

Solution:

Straining a SQL metaphor, as you always query a DynamoDB table not a database, you might consider the KeyConditionExpression analogous with the FROM keyword of a SQL Query which returns zero or more rows as a temporary table. The WHERE keyword used to refine this is FilterExpression in DynamoDB.

For example:

KeyConditionExpression = "PartitonKey = :v_VALUE1",
FilterExpression = "OtherKey = :v_VALUE2"