CODEWITHSUNDEEP
javaamazon-dynamodb
Denis Li
Denis Li

Reputation: 366

How to put a new key-value pair into a map in DynamoDB? (java)

I have a DynamoDB attribute whose value is a map from a Number to a String. I am trying to put in a new key-value pair. From what I've read, this seems to be possible, but I don't know how.

I assume the solution is similar to the one in the link below:

How to update a Map or a List on AWS DynamoDB document API?

But I do not believe the example is on putting in a new item to a map. Could someone show me how to put in an item to a map?

Thanks.

EDIT:

I do not want to get the item, locally make the changes, and put it back. I am working with multiple clients who might interact concurrently (and I assume the update by dynamo ensures there will be no race conditions).

Upvotes: 25

Views: 37791

Answers (2)

Surajit Kundu
Surajit Kundu

Reputation: 495

Visit http://www.tryyourskill.com/aws/insert-or-append-key-values-map-in-dynamodb-using-java may help you with the code snippet to add or append values in map column

public boolean insertKeyValue(String tableName, String primaryKey, String 
    primaryKeyValue, String updateColumn, String newKey, String newValue) {

    //Configuration to connect to DynamoDB
    Table table = dynamoDB.getTable(tableName);
    boolean insertAppendStatus = false;
    try {
        //Updates when map is already exist in the table
        UpdateItemSpec updateItemSpec = new UpdateItemSpec()
            .withPrimaryKey(primaryKey, primaryKeyValue)
            .withReturnValues(ReturnValue.ALL_NEW)
            .withUpdateExpression("set #columnName." + newKey + " = :columnValue")
            .withNameMap(new NameMap().with("#columnName", updateColumn))
            .withValueMap(new ValueMap().with(":columnValue", newValue))
            .withConditionExpression("attribute_exists("+ updateColumn +")");

        table.updateItem(updateItemSpec);
        insertAppendStatus = true;
    //Add map column when it's not exist in the table
    } catch (ConditionalCheckFailedException e) {
        HashMap<String, String> map =  new HashMap<>();
        map.put(newKey, newValue);
        UpdateItemSpec updateItemSpec = new UpdateItemSpec()
            .withPrimaryKey(primaryKey,primaryKeyValue)
            .withReturnValues(ReturnValue.ALL_NEW)
            .withUpdateExpression("set #columnName = :m")
            .withNameMap(new NameMap().with("#columnName", updateColumn))
            .withValueMap(new ValueMap().withMap(":m", map));

        table.updateItem(updateItemSpec);
        insertAppendStatus = true;
    } catch(Exception e) {
        e.printStackTrace();
    }
    return insertAppendStatus;
}

Upvotes: 6

Alexander Patrikalakis
Alexander Patrikalakis

Reputation: 5205

With the following arguments to UpdateItem, you can condition adding a map entry at #number when map.#number does not exist in the map already:

UpdateExpression = "SET map.#number = :string"
ExpressionAttributeNames = { "#number" : "1" }
ExpressionAttributeValues = { ":string" : "the string to store in the map at key value 1" }
ConditionExpression = "attribute_not_exists(map.#number)"

Upvotes: 47

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