javascript - How can I use transactions to check if an item exists in one table before updating a second table using AWS.DynamoD

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I am new to DynamoDB. I have a DynamoDB table called 'kids-profiles' that lists child profiles for a user (primary partition key 'userId', primary sort key 'childId'). I have a second table called 'kids-tasks' that lists tasks for a child (primary partition key 'childId', primary sort key 'taskId'). I would like to atomically add an item to the 'kids-tasks' table only if the 'childId' exists in the 'kids-profiles' table.

I am trying to use the transactWrite method of the AWS.DynamoDB.DocumentClient class (.html) to achieve this, but I can't get it to work. First, when I try to add a ConditionCheck to the TransactionItems, it says "TransactItems can only contain one of Check, Put, Update or Delete". So I have changed "ConditionCheck" to "Check" instead, assuming that is correct even though it is not mentioned in the documentation. Second, when I do get it to execute, it adds the task to the 'kids-tasks' table regardless of whether or not the 'childId' exists in the 'kids-profiles' table.

    const params = {
        TransactItems: [ 
            {
                Check: {
                    TableName: "kids-profiles",
                    Key: {
                        userId:   userId,
                        childId:  childId,
                    },
                    ConditionExpression: "attribute_exists(childId)",
                },
                Put: {
                    TableName: "kids-tasks",
                    Item: {
                        childId:  childId,
                        taskId:   uuid.v1(),
                        title:    title,
                    }
                }
            }
        ]
    };

    try 
    {
        await dynamoDb.transactWrite(params).promise();
        console.log("Success!");
    } 
    catch (error) 
    {
        console.log("Error");
    }

I am new to DynamoDB. I have a DynamoDB table called 'kids-profiles' that lists child profiles for a user (primary partition key 'userId', primary sort key 'childId'). I have a second table called 'kids-tasks' that lists tasks for a child (primary partition key 'childId', primary sort key 'taskId'). I would like to atomically add an item to the 'kids-tasks' table only if the 'childId' exists in the 'kids-profiles' table.

I am trying to use the transactWrite method of the AWS.DynamoDB.DocumentClient class (https://docs.aws.amazon./AWSJavaScriptSDK/latest/AWS/DynamoDB/DocumentClient.html) to achieve this, but I can't get it to work. First, when I try to add a ConditionCheck to the TransactionItems, it says "TransactItems can only contain one of Check, Put, Update or Delete". So I have changed "ConditionCheck" to "Check" instead, assuming that is correct even though it is not mentioned in the documentation. Second, when I do get it to execute, it adds the task to the 'kids-tasks' table regardless of whether or not the 'childId' exists in the 'kids-profiles' table.

    const params = {
        TransactItems: [ 
            {
                Check: {
                    TableName: "kids-profiles",
                    Key: {
                        userId:   userId,
                        childId:  childId,
                    },
                    ConditionExpression: "attribute_exists(childId)",
                },
                Put: {
                    TableName: "kids-tasks",
                    Item: {
                        childId:  childId,
                        taskId:   uuid.v1(),
                        title:    title,
                    }
                }
            }
        ]
    };

    try 
    {
        await dynamoDb.transactWrite(params).promise();
        console.log("Success!");
    } 
    catch (error) 
    {
        console.log("Error");
    }

• javascript
• amazon-dynamodb

Share Improve this question Follow asked May 3, 2019 at 21:33 SusanSusan 7111 silver badge33 bronze badges 4

• The Document client does not support transactions yet. – Matthew Pope Commented May 6, 2019 at 2:50
• So the documentation is inaccurate?? docs.aws.amazon./AWSJavaScriptSDK/latest/AWS/DynamoDB/… – Susan Commented May 6, 2019 at 13:29
• Is there another way I can achieve this then? – Susan Commented May 6, 2019 at 13:30
• My apologies. It does appear to be supported. I guess I missed the announcement when that was added to the SDK. – Matthew Pope Commented May 6, 2019 at 15:09

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1 Answer 1

Sorted by: Reset to default 16

Divide objects into individual Operations.

 const params = {
     TransactItems: [ 
         {
            ConditionCheck: {
                ...
            },
+        }, // <------ !!!!!
+        {
             Put: {
                ...
         }
     ]
 };

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