Query condition missed key schema element : Validation Error

In another answer @smcstewart responded to this question. But he provides a link instead of commenting why this error occurs. I want to add a brief comment hoping it will save your time.

AWS docs on Querying a Table states that you can do WHERE condition queries (e.g. SQL query SELECT * FROM Music WHERE Artist='No One You Know') in the DynamoDB way, but with one important caveat:

You MUST specify an EQUALITY condition for the PARTITION key, and you can optionally provide another condition for the SORT key.

Meaning you can only use key attributes with Query. Doing it in any other way would mean that DynamoDB would run a full scan for you which is NOT efficient - less efficient than using Global secondary indexes.

So if you need to query on non-key attributes using Query is usually NOT an option - best option is using Global Secondary Indexes as suggested by @smcstewart.

I found this guide to be useful to create a Global secondary index manually.

If you need to add it using CloudFormation here is a relevant page.

I was getting this error for a different scenario. Here is my scenario. (It's very unlikely that anyone else ends up with this case, but incase)

I had a query working on a Table (say table A). Table A had a partition key m_id and sort key u_id. I had a query to fetch data using m_id. The query was working.

'''

var queryParams = {
        ExpressionAttributeValues: {
          ':m_id': mId
         },
       KeyConditionExpression: 'm_id = :m_id',
       TableName: "A"
      };
    
   let connections = await docClient.query(queryParams).promise();

'''

I created another Table say Table B. I made some errors in naming keys so I simply deleted and created a table with the same name again, Table B. Table B had partition key m_id, and sort key s_id.

I copied pasted the same query which I was using for Table A, I changed Table name only because partition key had the same name.

To my shock, I get this expectation.

"ValidationException: Query condition missed key schema element"

I rechecked all the names, I compared the query with the working query. Everything was fine. I thought maybe because, I was deleting recreating Table B, it could be something with that. So I create a fresh Table with a new Name Table B2 with the same key names as Table B.

In my query that was throwing exceptions, I changed only the Table name from B to B2. And the Exception was gone.

If you are getting this on a fresh table, where no query has worked earlier, creating a new Table with a new name is an option.

If you delete a Table only to change partition key names, it may be safer to use a new name for Table as well (Dynamo could be referring metadata by table names and not by internal identifiers, it is possible that old metadata stays even if you delete a table. Just a guess given I faced this case).

---

EDIT:2022-July-12

This error does not leave me. My own answer was helpful but one more case, there was a trailing space in name of Key in the table. And Dynamo does not even check for spaces in key names.

You're trying to run a query using a condition that does not include the primary key. This is how queries work in DynamoDB. You would need to do a scan for the info in your case, however, I don't think that is the best option.

I think you want to set up a global secondary index and use that to query for the processing status.