DynamoDB iOS:AWSDynamoDBScanExpression为scanFilter属性提供多个参数

Question

首先，我试图用DynamoDB实现的目标：

->(我试图在登录系统的扫描过滤器中包括用户名和密码。因此，如果对于电子邮件/用户和密码组合，AWSDynamoDBObjectMapper的scan方法返回一个对象，则登录成功，否则为否。(

怎么了？

我一直在尝试阅读Github上的文档和示例代码，但似乎没有一个正确使用它的例子。从文档中我只发现scanFilter属于NSDictionary类型。所以我尝试包含多个用于过滤的参数(UserName/UserEmail and Password(，但它无法扫描结果。

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

然而，如果我只传递一个参数，它就会工作并返回一个对象，或者说一行数据库。

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

完整的代码供参考(当我提到同事的代码时，类似的代码适用于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 = @"[e-mail]";//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;
}];

任何建议/想法/意见都将不胜感激。

谢谢，罗翰。

Answer 1

您是否考虑过使用AWSDynamoDBScanInput和NSMutableDictionary？我在Swift中有以下例子，应该很容易翻译成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 = "[e-mail]"
    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

在处理类似问题时，我在这个线程上使用了存根。以下是我解决问题的方法：

    let objectMapper = AWSDynamoDBObjectMapper.default()
    let scanExpression = AWSDynamoDBScanExpression()
    scanExpression.filterExpression = "#UserNameOrUserEmail = :UserNameOrUserEmail AND #password = :follows"
    scanExpression.expressionAttributeNames = ["#UserNameOrUserEmail": "UserNameOrUserEmail" , "#password": "password" ,]
    scanExpression.expressionAttributeValues = [":UserNameOrUserEmail": "[e-mail]", ":password": password ,]
    objectMapper.scan(User.self, expression: scanExpression) { (response: AWSDynamoDBPaginatedOutput?, error: Error?) in
        // handle data or error here...
    }

只是以防万一它能帮助别人。