Qualifiers an be used parse or transform data returned from the Amazon DynamoDB.

Using the following External Object Qualifier, Sample_Qualifier_Field value will be automatically populated. As per the definition, it is PK + SK which means concatenation of PK and SK field values.

Sample External Object Qualifier:

{
  "tableName": "Test",
  "columns": {
    "Sample_Qualifier_Field": {
      "type": "S",
      "values": [
        {
          "definition": "PK + SK"
        }
      ]
    } 
  }
}

Sample Apex Code:

Test__x objTest = new Test__x();
objTest.PK__c = '7';
objTest.SK__c = 'Test7';
objTest.Name__c = 'Test7';
Database.SaveResult objSR = Database.insertImmediate( 
    objTest 
);
System.debug( 'Created successfully? ' + objSR.isSuccess() );
if ( objSR.isSuccess() ) {
    
    System.debug( 'Record Id is ' + objSR.getId() );
    
}

Output: