amazon-web-services - DynamoDB : Query all data and sorted by date descending

Question

我是 AWS DynamoDB 的新手，需要这里专家的指导。

我正在创建一个应用程序，该应用程序将显示一个事件列表，条件是事件日期必须大于今天日期，并按事件日期降序排列。我的表架构如下:

分区键 = eventid

排序键 = 事件日期

如果我使用关系数据库，我可以使用“SELECT * FROM events where eventdate > todaydate ORDERBY eventdate DESC”，但是我想如何使用 AWS DynamoDB 实现这一点？我希望使用 QUERY 而不是 SCAN。

Answer 1

根据 DynamoDB Query API Documentation :

Query :

A Query operation uses the primary key of a table or a secondary index to directly access items from that table or index.

Use the KeyConditionExpression parameter to provide a specific value for the partition key. The Query operation will return all of the items from the table or index with that partition key value. You can optionally narrow the scope of the Query operation by specifying a sort key value and a comparison operator in KeyConditionExpression. You can use the ScanIndexForward parameter to get results in forward or reverse order, by sort key.

KeyConditionExpression :

The condition that specifies the key value(s) for items to be retrieved by the Query action.

The condition must perform an equality test on a single partition key value. The condition can also perform one of several comparison tests on a single sort key value. Query can use KeyConditionExpression to retrieve one item with a given partition key value and sort key value, or several items that have the same partition key value but different sort key values.

The partition key equality test is required, and must be specified in the following format:

partitionKeyName = :partitionkeyval

If you also want to provide a condition for the sort key, it must be combined using AND with the condition for the sort key. Following is an example, using the = comparison operator for the sort key:

partitionKeyName = :partitionkeyval AND sortKeyName = :sortkeyval

Valid comparisons for the sort key condition are as follows:

• sortKeyName = :sortkeyval - true if the sort key value is equal to :sortkeyval.
• sortKeyName < :sortkeyval - true if the sort key value is less than :sortkeyval.
• sortKeyName <= :sortkeyval - true if the sort key value is less than or equal to :sortkeyval.
• sortKeyName > :sortkeyval - true if the sort key value is greater than :sortkeyval.
• sortKeyName >= :sortkeyval - true if the sort key value is greater than or equal to :sortkeyval.
• sortKeyName BETWEEN :sortkeyval1 AND :sortkeyval2 - true if the sort key value is greater than or equal to :sortkeyval1, and less than or equal to :sortkeyval2.
• begins_with ( sortKeyName, :sortkeyval ) - true if the sort key value begins with a particular operand. (You cannot use this function with a sort key that is of type Number.)

You can optionally use the ExpressionAttributeNames parameter to replace the names of the partition key and sort key with placeholder tokens. This option might be necessary if an attribute name conflicts with a DynamoDB reserved word. For example, the following KeyConditionExpression parameter causes an error because Size is a reserved word:

Size = :myval

To work around this, define a placeholder (such a #S) to represent the attribute name Size. KeyConditionExpression then is as follows:

#S = :myval

For a list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide.

For more information on ExpressionAttributeNames and ExpressionAttributeValues, see Using Placeholders for Attribute Names and Values in the Amazon DynamoDB Developer Guide.

Type: String

Required: No

您的场景可以转换为以下代码:

$tableName = "genericTable";
$response = $dynamodb->query([
    'TableName' => $tableName,
    'IndexName' => 'OrderCreationDateIndex',
    'KeyConditionExpression' => 'partitionKeyName = :partitionkeyval AND sortKeyName = :sortkeyval',
    'ExpressionAttributeValues' =>  [
        ':partitionkeyval' => ['S' => 'pkey'],
        ':sortkeyval' => ['S' => 'sortkey']
    ],
    'Select' => 'ALL_PROJECTED_ATTRIBUTES',
    'ScanIndexForward' => false,
    'ConsistentRead' => true,
    'Limit' => 5,
    'ReturnConsumedCapacity' => 'TOTAL'
]);