Question

I just started using the Android SDK for AWS SDB, and am encountering an unexpected result doing writes and reads. This is surely a simple problem, so I would appreciate any explanations!

Here’s the problem.

First, I write a record to SDB like this:

sdb.createDomain(new CreateDomainRequest("myDomain"));

List<ReplaceableAttribute> attributes = new ArrayList<ReplaceableAttribute>(1);
attributes.add(new ReplaceableAttribute().withName("myField").withValue(myField));

sdb.putAttributes(new PutAttributesRequest("myDomain", itemName, attributes));

I can see the value of myField is correctly written to SDB using the Chrome SdbNavigator.

Now I change the record using the same code, but with a different value for the myField attribute. Again, I can see that the record is written correctly with the new value using SdbNavigator.

Finally, I uninstall the app from the device (i.e., wipe it clean), reinstall the app, and run it again to execute the following code:

String s = "select * from `myDomain`";
SelectRequest selectRequest = new SelectRequest(s).withConsistentRead(true);
List items = sdb.select(selectRequest).getItems();

int count = items.size();

for (int i=0; i<count; i++) {
    Item item = (Item)(items.get(i));
    String itemName = item.getName();

    myField = getStringValueForAttributeFromList("myField", item.getAttributes());
}

where getStringValueForAttributeFromList() is defined as

protected String getStringValueForAttributeFromList( String attributeName, List<Attribute> attributes ) {
    for ( Attribute attribute : attributes ) {
        if ( attribute.getName().equals( attributeName ) ) {
            return attribute.getValue();
        }
    }
    return "";      
}

The unexpected part is that the getStringValueForAttributeFromList() function returns the first (now incorrect) value of the myField attribute – even though the sdbNavigator shows the record has the second (correct) value.

Any idea what is happening, and how to fix?? Thanks.

Answer 1

SOLVED: The issue I was facing is that SDB allows multiple attributes with the same name in the same record (item), so it was picking up the first value I set for the attribute myField.

If you want to guarantee uniqueness, you have to set a flag on the replaceable attribute as follows:

ReplaceableAttribute ra = new ReplaceableAttribute().withName("myField").withValue(myField);
ra.setReplace(true); attributes.add(ra);

and then call putAttributesRequest(), as above. Thanks.