Adding JSON array to DynamoDB Item

Question

I understand that I can create "Lists" only from primitive data types, so look at my (Node.js using AWS Document Client) code as pseudo code. My objective is to attach a JSON array to an item so that I can later retrieve/update/delete the device (and corresponding data) from the customer's record. I understand I may be able to use Maps to do this, but I'm a beginner and the documentation regarding how to do that using document client is unclear to me.

This is what I am trying to do:

var deviceData = {
    'deviceID': deviceID,
    'attributes': [
        {'firmwareVersion': firmwareVersion},
        {'productID': productID},
        {'knickName': 'New Device'},
        {'dateAdded': (new Date()).getTime()}
    ]
};

var newCustomerData = {
    TableName: process.env.customerMasterFile,
    Key: {
        'email': email
    },
    ReturnValues: 'UPDATED_NEW',
    UpdateExpression: 'ADD #device :device SET #customerEmailDomain = :customerEmailDomain, #friendlyName = :friendlyName, #created = :created, #updated = :updated',
    ExpressionAttributeNames: {
        '#device': 'deviceList',
        '#customerEmailDomain': 'customerEmaiDomain',
        '#friendlyName': 'friendlyName',
        '#created': 'createAccountTime',
        '#updated': 'updateAccountTime',
    },
    ExpressionAttributeValues: {
        ':device': docClient.createSet([deviceData]),  // I know this is incorrect...
        ':customerEmailDomain': customerEmailDomain,
        ':friendlyName': friendlyName,
        ':created': (new Date()).getTime(),
        ':updated': (new Date()).getTime()
    }
};

docClient.update(newCustomerData, function(err, data) {
    if (err) console.log(err);
    else console.log(data);
});

notionquest · Accepted Answer · 2017-04-01 14:58:47Z

2

Normally, JSON data will be persisted as Map on DynamoDB. If you store JSON array on DynamoDB, it will be stored as "List of Map" data type on DynamoDB which will make it difficult to update, delete, retrieve without knowing the index of the List data type (i.e. device). It is not recommended to use "List of Map" if you need to accomplish update/delete without knowing the index of list (i.e. index of an array).

1) Changed to SET for all attributes including device

To store single JSON object as Map which will allow to update/delete without knowing the index of an array:-

var params = {
    TableName: process.env.customerMasterFile,
    Key: {
        'email': email
    },
    ReturnValues: 'UPDATED_NEW',
    UpdateExpression: 'SET #device = :device, #customerEmailDomain = :customerEmailDomain ,#friendlyName = :friendlyName, #created = :created, #updated = :updated',
    ExpressionAttributeNames: {
        '#device': 'deviceList',
        '#customerEmailDomain': 'customerEmaiDomain',
        '#friendlyName': 'friendlyName',
        '#created': 'createAccountTime',
        '#updated': 'updateAccountTime',
    },
    ExpressionAttributeValues: {
        ':device': deviceData,
        ':customerEmailDomain': customerEmailDomain,
        ':friendlyName': friendlyName,
        ':created': (new Date()).getTime(),
        ':updated': (new Date()).getTime()
    }
};

Sample device as Map:-

Alternate Approach:-

Add device id as sort key of the table
The attributes email and device id forms the unique combination for an item on DynamoDB
You can accomplish the update/delete easily with this data model

answered Apr 1, 2017 at 14:58

notionquest

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7 Comments

Jim from Princeton Over a year ago

thanks for your thoughtful response. As I understand it, Sort Key added to my table with a Primary Key creates a sort of composite identifier. It is possible in our database not to have a device (ergo no deviceID) assigned to an account. Would I then try to store a 'null' object in deviceID in the case, for example, where user 1) creates account where no device is attached or 2) modifies/updates/deletes such that all attached devices are removed fro user's account?

notionquest Over a year ago

No, that is not possible. Sort key is must for an item.

Jim from Princeton Over a year ago

Sort Key value may be non-unique vis-à-vis the rest of the table (unique within the Item), I take it. I think I may then write in a dummy object that would allow me to easily/rapidly get the item with a {'email':email, 'deviceID': 'dummy'} pair. Or, is there a simpler/better/easier way that I am overlooking?

notionquest Over a year ago

Yes, this should be fine. But you can't update the sort key value once the item is created. An user will have a item with dummy device object item when account is created without device. When the device is attached, you may need to create a new item for the email and device id. Hope that is fine.

notionquest Over a year ago

No, you can create. The combination of Partition key and Sort key should be unique. You can have multiple items with same email id having different device ids (including dummy id).

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