how to query or search with one Primary Key and One Attribute in DynamoDb

Question

i have database like this :

Symbol are primaryKey and priceId is SortKey and others are attributes priceId as sortkey always unique

i have information only symbol and savetime

for example is

String Symbols = "EURUSD"; String time = "2020-06-10 09:12:07";

i have try use scan but my code stack

Table table = dynamoDB.getTable(tableName);
        System.out.println("runFirstTime For Search Data");
        String Symbols = "EURUSD";
        String time = "2020-06-10 09:12:07";
        try{
            Map<String, AttributeValue> expressionAttributeValues = new HashMap<String, AttributeValue>(); 
            expressionAttributeValues.put(":savetime", new AttributeValue().withS(time));
            expressionAttributeValues.put(":symbol", new AttributeValue().withS(Symbols));
            ScanRequest scanRequest = new ScanRequest().withTableName(tableName).withFilterExpression("savetime = :savetime AND symbol = :symbol")
                    .withProjectionExpression("symbol, priceId, savetime, Price").withExpressionAttributeValues(expressionAttributeValues);
            ScanResult result = client.scan(scanRequest);
            for (Map<String, AttributeValue> item : result.getItems()) {
                System.out.println(item);
            }
        }catch (Exception e) {
             System.err.println("Cannot retrieve items.");
             System.err.println(e.getMessage());
          }
    }

my code stack in log4j:WARN No appenders could be found for logger

(com.amazonaws.AmazonWebServiceClient).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
runFirstTime For Search Data

i also have try use query and change my database structure like this

and i have try to code use this

Table table = dynamoDB.getTable(tableName);
        System.out.println("runFirstTime For Search Data");
        String Symbols = "EURUSD";
        String time = "2020-06-10 11:43:31";
        String Prefix = "Onezero";
          ItemCollection<QueryOutcome> items = null;
            Iterator<Item> iterator = null;
            Item item = null;
        try{
            QuerySpec spec = new QuerySpec().withProjectionExpression("symbol, priceId, Price, savetime")
                    .withKeyConditionExpression("symbol = :v_symbol and begin_with(priceId, :begin)")
                    .withFilterExpression("savetime = :v_savetime")
                    .withValueMap(new ValueMap()
                            .withString(":v_symbol", Symbols)
                            .withString("begin", Prefix)
                            .withString(":v_savetime", time));
            items = table.query(spec);
            iterator = items.iterator();
            while (iterator.hasNext()) {
                item = iterator.next();
                System.out.println(item.getString("symbol") + ": " + item.getString("savetime") + ": "+ item.getString("Price"));
            }

        }catch (Exception e) {
             System.err.println("Cannot retrieve items.");
             System.err.println(e.getMessage());
          }
    }

but i still got an error like this one

ExpressionAttributeValues contains invalid key: Syntax error; key: "begin" (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException; Request ID: 5TTRE1Q7FBT5TLNL0MTTPV05K7VV4KQNSO5AEMVJF66Q9ASUAAJG; Proxy: null)

why like that ? maybe error in scan. so what is best to use to search from 1 key and 1 attribute use dynamoDb ? any example for that ?

i have try use getitem or scan but still have problem

score 1 · Answer 1 · answered Jun 11 '20 at 07:19

this problem done when i use this code

Table table = dynamoDB.getTable(tableName);
        System.out.println("runFirstTime For Search Data");
        String Symbols = "EURUSD";
        String time = "2020-06-11 03:20:52";
        String Prefix = "Onezero";
          ItemCollection<QueryOutcome> items = null;
            Iterator<Item> iterator = null;
            Item item = null;
        try{
            QuerySpec spec = new QuerySpec().withProjectionExpression("symbol, priceId, Price, savetime")
                    .withKeyConditionExpression("symbol = :v_symbol and begins_with(priceId, :begin)")
                    .withFilterExpression("begins_with(savetime, :v_savetime)")
                    .withValueMap(new ValueMap()
                            .withString(":v_symbol", Symbols)
                            .withString(":begin", Prefix)
                            .withString(":v_savetime", time));
            items = table.query(spec);
            iterator = items.iterator();
            while (iterator.hasNext()) {
                item = iterator.next();
                System.out.println(item.getString("symbol") + ": " + item.getString("savetime") + ": "+ item.getString("Price"));
            }

        }catch (Exception e) {
             System.err.println("Cannot retrieve items.");
             System.err.println(e.getMessage());
          }

thanks for everyone help here.

score 0 · Accepted Answer · answered Jun 10 '20 at 11:27

0

You seem to be mixing multiple issues here...

For your DynamoDB query: I think, you should probably use a KeyConditionExpression to filter for symbol (because that is your partition key) combined with a FilterExpression for savetime. The docs provide some examples: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/QueryingJavaDocumentAPI.html

Be aware: DynamoDB will load all entries which match the KeyConditionExpression (i.e. this is the load you will pay for) and apply the FilterExpression afterwards. But that is the expected behaviour, you can restrict the query only by your keys.

For your log4j warning, please check the answers to the questions here:

answered Jun 10 '20 at 11:27

Iris Hunkeler

208
1
10

what is different use scan and query ? – yuyu kungkung Jun 10 '20 at 11:39
scan always scans the whole table (so they are not very efficient). with query you can use filters on your partition and search key. Check this page in the AWS docs: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/bp-query-scan.html – Iris Hunkeler Jun 10 '20 at 12:00
okay i have update my question i have try use query can you give me what wrong in my code ? – yuyu kungkung Jun 10 '20 at 12:11
not sure if it is the only issue, but you seem to have a typo: ```begin_with``` should be ```begins_with``` . See also https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.OperatorsAndFunctions.html – Iris Hunkeler Jun 10 '20 at 12:31

how to query or search with one Primary Key and One Attribute in DynamoDb

2 Answers2