使用哈希值数组的AWS DynamoDB Scan和FilterExpression

Question

我很难找到一个在DynamoDB表上使用FilterExpression进行扫描的有用示例.我在浏览器中使用javascript SDK.

我想扫描我的表并返回那些在传递给Scan的数组中具有HASH字段"UID"值的记录

让我说我有一个唯一的ID数组,我的表的哈希字段我想从我的DynamoDB表中查询这些记录.

像下面的东西

var idsToSearch=['123','456','789'] //array of the HASH values I would like to retrieve
var tableToSearch = new AWS.DynamoDB();
var scanParams = {
  "TableName":"myAwsTable",  
  "AttributesToGet":['ID','COMMENTS','DATE'],  
  "FilterExpression":"'ID' in "+idsToSearch+"" 

}
tableToSearch.scan(scanParams), function(err,data){
    if (err) console.log(err, err.stack); //error handler
    else console.log(data); //success response
})

Answer 1

你应该使用IN运营商.对于属性名称和属性值,使用占位符也更容易.但是,我建议不要Scan在这种情况下使用a.听起来您已经拥有了要查找的哈希键属性值,因此使用它会更有意义BatchGetItem.

无论如何,这是你在Java中如何做到这一点:

ScanSpec scanSpec = new ScanSpec()
    .withFilterExpression("#idname in (:val1, :val2, :val3)")
    .withNameMap(ImmutableMap.of("#idname", "ID"))
    .withValueMap(ImmutableMap.of(":val1", "123", ":val2", "456", ":val23", "789"));
ItemCollection<ScanOutcome> = table.scan(scanSpec);

我会想象使用Javascript SDK会是这样的:

var scanParams = {
  "TableName":"myAwsTable",
  "AttributesToGet": ['ID','COMMENTS','DATE'],
  "FilterExpression": '#idname in (:val1, :val2, :val3)',
  "ExpressionAttributeNames": {
    '#idname': 'ID'
  },
  "ExpressionAttributeValues": {
    ':val1': '123',
    ':val2': '456',
    ':val3': '789'
  }
}

Answer 2

我有这个问题并通过使用contains参数找出它

// Object stored in the DB looks like this: 
// [
//     'name' => 'myName',
//     'age' => '24',
//     'gender' => 'Male',
//     'visited' => [
//          'countries': ['Canada', 'USA', 'Japan', 'Australia'],
//          'last_trip': '2015/12/13',
//          'reviews_written': 20
//     ]
// 
// ];

$countries = ['Canada', 'USA', 'Japan', 'Australia'];

$paramToMatch = '24';

$client->query([
        'TableName'     => 'MyDyanmoDB',
        'KeyConditions' => [
            'age' => [
                'AttributeValueList' => [
                    $marshaler->marshalValue($paramToMatch)
                ],
                'ComparisonOperator' => 'EQ'
            ]
        ],
        'ExpressionAttributeNames' => [
            '#visited'   => 'visited',
            '#countries' => 'countries'
        ],
        'ExpressionAttributeValues' => [
            ':countries' => $marshaler->marshalValue($countries)
        ],
        'FilterExpression' => 'contains(:countries, #visited.#countries)',
]);

Answer 3

以下是我如何使用“扫描”来获取具有特定 ID（“ContentID”）的项目，如下例所示：

var params = {
    TableName: environment.ddbContentTableName,
    ProjectionExpression: "Title, ContentId, Link",
    FilterExpression: "ContentId in (:contentId1, :contentId2, :contentId3, :contentId4)",
    ExpressionAttributeValues: {":contentId1":102,":contentId2":104,":contentId3":103,":contentId4":101}
};

var docClient = new AWS.DynamoDB.DocumentClient();
docClient.scan(params, onQuery); 

然后，我可以根据已知值以编程方式构造 FilterExpression 和 ExpressionAttributeValues，例如

    // Create the FilterExpression and ExpressionAttributeValues
    var filterExpression =  "ContentId in ("; 

    var expressionAttributeValues = {};

    for (var i = 0; i < currentFavorites.length; i++) { 
        var contentIdName = ":contentId"+(i+1);
        
        if (i==0) {
            filterExpression = filterExpression + contentIdName;
        } else {
            filterExpression = filterExpression + ", " + contentIdName;
        }

        expressionAttributeValues[contentIdName] = currentFavorites[i];
    }

    filterExpression = filterExpression + ")";

    var params = {
        TableName: environment.ddbContentTableName,
        ProjectionExpression: "Title, ContentId, Link",
        FilterExpression: filterExpression,
        ExpressionAttributeValues: expressionAttributeValues
    };

    var docClient = new AWS.DynamoDB.DocumentClient();
    docClient.scan(params, onQuery);