DynamoDB iOS : AWSDynamoDBScanExpression Provide multiple parameters for scanFilter property

Question

Firstly, what I am trying to achieve with DynamoDB:

-> (I am trying to include username and password in scan filter for login system. So if for email/user and password combination, scan method of AWSDynamoDBObjectMapper returns an object, login is successful otherwise no.)

What's going wrong?

I have been trying to read documentation and sample code on Github for this but none seems to have example of proper use of it. From documentation I only found that scanFilter is of type NSDictionary. So I tried to include multiple parameters for filtering (UserName/UserEmail and Password) and it is failing to scan results.

 scanExpression.scanFilter = @{@"Password": passwordCondition, UserNameOrUserEmail : usernameOrEmailCondition};

However if I pass only one parameter it works and returns an object, or lets say a row of a database.

scanExpression.scanFilter = @{@"Password": passwordCondition};

Full code for reference (Similar code for Android works fine, when I referred to colleague's, who is doing Android.):

// Check if email or username and decide DynamoDB Attribute accordingly.
NSString *UserNameOrUserEmail;   
if ([usernameOrEmail rangeOfString:@"@"].location == NSNotFound) 
    UserNameOrUserEmail = @"UserName";
else
    UserNameOrUserEmail = @"UserEmail";

AWSDynamoDBScanExpression *scanExpression = [AWSDynamoDBScanExpression new];

AWSDynamoDBCondition *passwordCondition = [AWSDynamoDBCondition new];
AWSDynamoDBAttributeValue *passwordAttribute = [AWSDynamoDBAttributeValue new];
passwordAttribute.S = password;
passwordCondition.attributeValueList = @[passwordAttribute];
passwordCondition.comparisonOperator = AWSDynamoDBComparisonOperatorEQ;

AWSDynamoDBCondition *usernameOrEmailCondition = [AWSDynamoDBCondition new];
AWSDynamoDBAttributeValue *usernameOrEmailAttribute = [AWSDynamoDBAttributeValue new];
usernameOrEmailAttribute.S = @"[email protected]";//usernameOrEmail;
usernameOrEmailCondition.attributeValueList = @[usernameOrEmailAttribute];
usernameOrEmailCondition.comparisonOperator = AWSDynamoDBComparisonOperatorEQ;

//Apply filter condtions: http://stackoverflow.com/a/27856299/818506
scanExpression.scanFilter = @{@"Password": passwordCondition, UserNameOrUserEmail : usernameOrEmailCondition}; //@{@"UserEmail": usernameOrEmailCondition};//

 //^^^^^^^^^^^^^^^^^^^^^^^^^^^Is this correct?^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^    

//Perform a scan:
[[dynamoDBObjectMapper scan:[User class] expression:scanExpression]continueWithBlock: ^id (AWSTask *task){

    if (task.error) {
        NSLog(@"The request failed. Error: [%@]", task.error);
    }
    if (task.exception) {
        NSLog(@"The request failed. Exception: [%@]", task.exception);
    }
    if (task.result) {
        AWSDynamoDBPaginatedOutput *paginatedOutput = task.result;
        for (User *user in paginatedOutput.items) {
            isLoginSuccessful = YES;
         }
        completionHandler(isLoginSuccessful);
    }
    return nil;
}];

Any suggestion/idea/comment would be appreciate.

Thanks, Rohan.

Answer 1

Have you considered using AWSDynamoDBScanInput and a NSMutableDictionary? I have the following example in Swift that should be fairly easy to translate to Objective-C:

    // create password condition
    let passwordCondition = AWSDynamoDBCondition()
    let v1    = AWSDynamoDBAttributeValue(); v1.S = password
    passwordCondition.comparisonOperator = AWSDynamoDBComparisonOperator.EQ
    passwordCondition.attributeValueList = [ v1 ]

    // create username condition        
    let usernameCondition = AWSDynamoDBCondition()
    let v2    = AWSDynamoDBAttributeValue(); v2.S = "[email protected]"
    usernameCondition.comparisonOperator = AWSDynamoDBComparisonOperator.EQ
    usernameCondition.attributeValueList = [ v2 ]

    // add these conditions to a NSMutableDictionary
    var scanFilterDict : NSMutableDictionary! = NSMutableDictionary()
    scanFilterDict.addEntriesFromDictionary(["password": passwordCondition])
    scanFilterDict.addEntriesFromDictionary(["UserNameOrUserEmail": usernameCondition])

    // use the mutable dictionary as scan filter
    scanInput.scanFilter = scanFilterDict as Dictionary<NSObject, AnyObject>
    scanInput.exclusiveStartKey = self.lastEvaluatedKey
    scanInput.limit = 20
    scanInput.tableName = "yourDynamoDBTable"

    // apply AND operator on both conditions
    scanInput.conditionalOperator = AWSDynamoDBConditionalOperator.And

    AWSDynamoDB.defaultDynamoDB().scan(input)

Answer 2

I stubbled on this thread while working on a similar problem. Here is how I solved it:

    let objectMapper = AWSDynamoDBObjectMapper.default()
    let scanExpression = AWSDynamoDBScanExpression()

    scanExpression.filterExpression = "#UserNameOrUserEmail = :UserNameOrUserEmail AND #password = :follows"
    scanExpression.expressionAttributeNames = ["#UserNameOrUserEmail": "UserNameOrUserEmail" , "#password": "password" ,]
    scanExpression.expressionAttributeValues = [":UserNameOrUserEmail": "[email protected]", ":password": password ,]

    objectMapper.scan(User.self, expression: scanExpression) { (response: AWSDynamoDBPaginatedOutput?, error: Error?) in
        // handle data or error here...
    }

Just it case it helps someone else.