查询DynamoDB [英] Querying DynamoDB
问题描述
我有一个DynamoDB表，其中包含一个字母数字字符串作为哈希键（例如 d4ed6962-3ec2-4312-a480-96ecbb48c9da）。我需要根据表中的另一个字段查询表，因此我需要查询以选择所有键，例如我的字段x在日期x和日期y之间。
I've got a DynamoDB table with a an alpha-numeric string as a hash key (e.g. "d4ed6962-3ec2-4312-a480-96ecbb48c9da"). I need to query the table based on another field in the table, hence I need my query to select all the keys such as my field x is between dat x and date y.
我知道我需要一个哈希键条件和一个范围键条件，但是我很难组成一个哈希键条件，该条件不能将查询绑定到特定ID。
I know I need a condition on the hash key and another on a range key, however I struggle to compose a hash key condition that does not bind my query to specific IDs.
我认为我可以根据ID为NOT_NULL来避免出现冗余情况，但是当我使用它时，会出现错误：
I thought I could get away with a redundant condition based on the ID being NOT_NULL, but when I use it I get the error:
不支持查询关键条件
Query key condition not supported
以下是我正在使用的条件，是否知道如何实现此目标？
Below is the conditions I am using, any idea how to achieve this goal?
Condition hashKeyCondition = new Condition()
.withComparisonOperator(ComparisonOperator.NOT_NULL.toString());
Condition rangeCondition = new Condition()
.withComparisonOperator(ComparisonOperator.BETWEEN.toString())
.withAttributeValueList(new AttributeValue().withS(dateFormatter.print(lastScanTime())),
new AttributeValue().withS(dateFormatter.print(currentScanTime)));
Map<String, Condition> keyConditions = new HashMap<String, Condition>();
keyConditions.put("userId", hashKeyCondition);
keyConditions.put("lastAccesTime", rangeCondition);
在此先感谢大家的帮助。
Thanks in advance to everyone helping.
推荐答案
在DynamoDB中，您可以使用3种api获取项目：
In DynamoDB you can get items with 3 api:
。 扫描（灵活但价格昂贵），
. Scan (flexible but expensive),
。 查询（不太灵活：您必须指定哈希，但是便宜些）
. Query (less flexible: you have to specify an hash, but less expensive)
。 GetItem （由哈希表示，如果您的表有一个，则由范围）
. GetItem (by Hash and, if your table has one, by range)
实现您想要的唯一方法是：
The only way to achieve what you want is by either:
-
使用扫描，速度慢或昂贵。
Use Scan, and be slow or expensive.
使用另一个表（B）作为上一个表（A）的索引，例如：
Use another table (B) as an index to the previous one (A) like:
B.HASH ='VALUES'
B.RANGE = userid
B.lastAccesTime = lastAccesTime（带有二级索引）
B.HASH = 'VALUES'
B.RANGE = userid
B.lastAccesTime = lastAccesTime (with a secondary index)
现在您必须在写入时保持该索引，但是可以将其与Query操作一起使用，将
用于获取您的userId。查询B：hash = VALUES，在x和y之间的lastaccessTime，选择用户ID。
Now you have to maintain that index on writes, but you can use it with the Query operation, to get your userIds. Query B: hash='VALUES', lastaccessTime between x and y, select userid.
希望这会有所帮助。
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