我最近为我在 Swift 中开发的 iOS 应用程序实现了 AWS 开发工具包。我已连接到我的数据库实例并且能够获得查询响应，但是，我正在努力将其转换为可用数据。我对 Swift、AWS 和一般编程还比较陌生，所以可能遗漏了一些明显的东西!

我的代码如下:

    let atVal = AWSDynamoDBAttributeValue()
    atVal.S = "123456abc"
    let condition = AWSDynamoDBCondition()
    condition.comparisonOperator = AWSDynamoDBComparisonOperator.EQ
    condition.attributeValueList = [atVal]

    let myDic: [String: AWSDynamoDBCondition] = ["userid": condition]
    let query = AWSDynamoDBQueryInput()
    query.indexName = "userid-index"
    query.tableName = "users"
    query.keyConditions = myDic
    query.limit = 1


    dynamoDB.query(query).continueWithBlock {
        (task: BFTask!) -> AnyObject! in
        let results = task.result as AWSDynamoDBQueryOutput

        let myResults = results.items
        println("object: \(myResults.description)")

        return nil
    }

控制台的输出是:

对象:[{ area = "{\n S =\"西汉普斯特德\";\n}"; name = "{\n S =\"Olly Mayes\";\n}"; userid = "{\n S =\"123456abc\";\n}"; }]

可以理解，使用 AWS 和 Swift 似乎没有太多优先级，因此我们将不胜感激!

最佳答案

您问题的简单答案是:将返回的 JSON 字符串转换为 Dictionary 对象。 像这样:

let data = jsonDataItem.dataUsingEncoding(NSUTF8StringEncoding)

    if data != nil {
        var error : NSError?
        let dict = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.AllowFragments, error: &error) as? NSDictionary

        if let e = error {
            ...
        } else {
            ...
        }

但是，我强烈建议您查看更高级别的 DynamoDB 映射器类 使用 DynamoDB 映射器类时，您定义数据结构，并将其提供给 DynamoDB Mapper .这是一个完整的示例，从表创建到表删除。该示例使用 DynamoDB Mapper 插入、删除、扫描和查询表。

首先需要初始化客户端SDK

    let cp = AWSStaticCredentialsProvider(accessKey: "AK...", secretKey: "xxx")
    let configuration = AWSServiceConfiguration(region: AWSRegionType.USEast1, credentialsProvider: cp)
    AWSServiceManager.defaultServiceManager().setDefaultServiceConfiguration(configuration)

这只是一个示例。在代码中嵌入访问 key 和 secret key 不是一个好习惯。最佳做法是使用 AWSCognitoCredentialsProvider相反(read more about Cognito)。

定义一个映射表中项目的类

class Item : AWSDynamoDBModel, AWSDynamoDBModeling {

    var email  : String = ""
    var date   : String = ""
    var note   : String = ""
    var number : Double = 0.0

    override init!() { super.init() }

    required init!(coder: NSCoder!) {
        fatalError("init(coder:) has not been implemented")
    }

    class func dynamoDBTableName() -> String! {
        return "Demo"
    }
    class func hashKeyAttribute() -> String! {
        return "email"
    }
    class func rangeKeyAttribute() -> String! {
        return "date"
    }

    //required to let DynamoDB Mapper create instances of this class
    override init(dictionary dictionaryValue: [NSObject : AnyObject]!, error: NSErrorPointer) {
        super.init(dictionary: dictionaryValue, error: error)
    }

    //workaround to possible XCode 6.1 Bug : "Type NotificationAck" does not conform to protocol "NSObjectProtocol"
    override func isEqual(anObject: AnyObject?) -> Bool {
        return super.isEqual(anObject)
    } }

创建表

self.createTable().continueWithSuccessBlock {(task: BFTask!) -> BFTask! in
    NSLog("Create table - success")
    return nil
}


func createTable() -> BFTask! {
    let pt = AWSDynamoDBProvisionedThroughput()
    pt.readCapacityUnits  = 10
    pt.writeCapacityUnits = 10

    let emailAttr = AWSDynamoDBAttributeDefinition()
    emailAttr.attributeName = "email"
    emailAttr.attributeType = AWSDynamoDBScalarAttributeType.S

    let dateAttr = AWSDynamoDBAttributeDefinition()
    dateAttr.attributeName = "date"
    dateAttr.attributeType = AWSDynamoDBScalarAttributeType.S

    let emailKey = AWSDynamoDBKeySchemaElement()
    emailKey.attributeName = "email"
    emailKey.keyType = AWSDynamoDBKeyType.Hash

    let dateKey = AWSDynamoDBKeySchemaElement()
    dateKey.attributeName = "date"
    dateKey.keyType = AWSDynamoDBKeyType.Range

    let ct = AWSDynamoDBCreateTableInput()
    ct.tableName = "Demo"
    ct.provisionedThroughput = pt
    ct.attributeDefinitions = [emailAttr, dateAttr]
    ct.keySchema = [ emailKey, dateKey ]

    NSLog("Creating table")

    let client = AWSDynamoDB.defaultDynamoDB()
    return client.createTable(ct)
}

删除表

self.deleteTable().continueWithSuccessBlock({ (task: BFTask!) -> BFTask! in
    NSLog("Delete table - success")
    return nil
})

func deleteTable() -> BFTask! {

    let dt = AWSDynamoDBDeleteTableInput()
    dt.tableName = "Demo"

    NSLog("Deleting table")
    let client = AWSDynamoDB.defaultDynamoDB()
    return client.deleteTable(dt)
}

插入项目

self.insertSomeItems().continueWithBlock({
    (task: BFTask!) -> BFTask! in

    if (task.error != nil) {
        NSLog(task.error.description)
    } else {
        NSLog("DynamoDB save succeeded")
    }

    return nil;
})

func insertSomeItems() -> BFTask! {
    let mapper = AWSDynamoDBObjectMapper.defaultDynamoDBObjectMapper()

    var item = Item()
    item.email  = "stormacq@amazon.com"
    item.date   = "20141101"
    item.note   = "This is item #1"
    item.number = 1.0
    let task1 = mapper.save(item)

    item = Item()
    item.email  = "stormacq@amazon.com"
    item.date   = "20141102"
    item.note   = "This is item #2"
    item.number = 2.0
    let task2 = mapper.save(item)

    item = Item()
    item.email  = "stormacq@amazon.lu"
    item.date   = "20141103"
    item.note   = "This is item #3"
    item.number = 3.0
    let task3 = mapper.save(item)

    return BFTask(forCompletionOfAllTasks: [task1, task2, task3])
}

加载单个项目

self.load("stormacq@amazon.com", range:"20141101").continueWithSuccessBlock({ (task: BFTask!) -> BFTask! in
    NSLog("Load one value - success")
    let item = task.result as Item
    print(item)
    return nil
})


func load(hash: String, range: String) -> BFTask! {
    let mapper = AWSDynamoDBObjectMapper.defaultDynamoDBObjectMapper()
    return mapper.load(Item.self, hashKey: hash, rangeKey: range)

}

查询哈希和范围键

/* 
   keyConditions
   http://docs.aws.amazon.com/AWSiOSSDK/latest/Classes/AWSDynamoDBQueryInput.html#//api/name/keyConditions
*/
let cond = AWSDynamoDBCondition()
let v1    = AWSDynamoDBAttributeValue(); v1.S = "20141101"
cond.comparisonOperator = AWSDynamoDBComparisonOperator.EQ
cond.attributeValueList = [ v1 ]
let c = [ "date" : cond ]
self.query("stormacq@amazon.com", keyConditions:c).continueWithSuccessBlock({ (task: BFTask!) -> BFTask! in
    NSLog("Query multiple values - success")
    let results = task.result as AWSDynamoDBPaginatedOutput
    for r in results.items {
        print(r)
    }
    return nil
})

func query(hash: String, keyConditions:[NSObject:AnyObject]) -> BFTask! {
    let mapper = AWSDynamoDBObjectMapper.defaultDynamoDBObjectMapper()

    let exp = AWSDynamoDBQueryExpression()
    exp.hashKeyValues      = hash
    exp.rangeKeyConditions = keyConditions

    return mapper.query(Item.self, expression: exp)
}

扫描项目(全表扫描)

let cond = AWSDynamoDBCondition()
let v1    = AWSDynamoDBAttributeValue(); v1.S = "20141101"
cond.comparisonOperator = AWSDynamoDBComparisonOperator.GT
cond.attributeValueList = [ v1 ]

let exp = AWSDynamoDBScanExpression()
exp.scanFilter = [ "date" : cond ]

self.scan(exp).continueWithSuccessBlock({ (task: BFTask!) -> BFTask! in
    NSLog("Scan multiple values - success")
    let results = task.result as AWSDynamoDBPaginatedOutput
    for r in results.items {
        print(r)
    }
    return nil
})

func scan(expression : AWSDynamoDBScanExpression) -> BFTask! {

    let mapper = AWSDynamoDBObjectMapper.defaultDynamoDBObjectMapper()
    return mapper.scan(Item.self, expression: expression)
}

如果您在美国东部 1 没有使用 DynamoDB，则运行此示例不会产生任何相关费用，因为它属于 DynamoDB's free tier .

关于amazon-web-services - 使用 Swift 进行 Amazon AWS DynamoDB 查询的最佳方式？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/26958637/