I have the following List example:

{
  "favorites": [
    {
      "createdAt": 1448998673852,
      "entityId": "558da3de395b1aee2d6b7d2b",
      "type": "media"
    },
    {
      "createdAt": 1448998789252,
      "entityId": "558da3de395b1aee2d6b7d83",
      "type": "media"
    },
    {
      "createdAt": 1448998793729,
      "entityId": "558da3de395b1aee2d6b7d99",
      "type": "media"
    },
    {
      "createdAt": 1448998813023,
      "entityId": "558da3de395b1aee2d6b7daf",
      "type": "media"
    }
  ],
  "userId": "2"
}

And I want to remove the Map with: "entityId": "558da3de395b1aee2d6b7d2b".

I am thinking an UpdateItem query, I have looked at REMOVE expression documentation (.Modifying.html), but I can't seem to see any examples, beyond removing items from a List by index value....

I have the following List example:

{
  "favorites": [
    {
      "createdAt": 1448998673852,
      "entityId": "558da3de395b1aee2d6b7d2b",
      "type": "media"
    },
    {
      "createdAt": 1448998789252,
      "entityId": "558da3de395b1aee2d6b7d83",
      "type": "media"
    },
    {
      "createdAt": 1448998793729,
      "entityId": "558da3de395b1aee2d6b7d99",
      "type": "media"
    },
    {
      "createdAt": 1448998813023,
      "entityId": "558da3de395b1aee2d6b7daf",
      "type": "media"
    }
  ],
  "userId": "2"
}

And I want to remove the Map with: "entityId": "558da3de395b1aee2d6b7d2b".

I am thinking an UpdateItem query, I have looked at REMOVE expression documentation (http://docs.aws.amazon./amazondynamodb/latest/developerguide/Expressions.Modifying.html), but I can't seem to see any examples, beyond removing items from a List by index value....

• javascript
• node.js
• amazon-web-services
• amazon-dynamodb

• I am facing similar issue. Did you figure out a solution for this? – ferrari16 Commented Apr 5, 2017 at 19:12
• Ditto. I'm having trouble as well. – ephemeralCoder Commented Apr 11, 2017 at 17:39

3 Answers 3

I've run into this issue a few times now, and unfortunately there's no straightforward solution. The two most mon workarounds I've e across are:

A. use a map instead of a list, you can reference the favorite directly in your update expression now using #favorites.#entityId. If order is important, add an order attribute to each map. In your data access layer is where you would need to do your conversions to/from the desired array type.

{
  "userId": "2",
  "favorites": {
    "558da3de395b1aee2d6b7d2b": {
      "createdAt": 1448998673852,
      "entityId": "558da3de395b1aee2d6b7d2b",
      "type": "media",
    },
    // ... more entities here
  }
}

B. use one-to-many tables instead, see http://docs.aws.amazon./amazondynamodb/latest/developerguide/GuidelinesForItems.html

I have done this before in Python using the Boto3 library but not in Javascript. I have a link to the Javascript delete item function. What I did in Python was that I queried my table for the item(s) and make a list of the primary keys of the objects I wanted deleted and called the delete function.

You should be de serializing the object into something you can work with, modifying it to remove that entry, then using update-item to save the changes.

I'm not a node.js user, but how did you create the object in the first place? Are you hand crafting the json string? If so you shouldn't be. There are libraries to handle json, and making it easy for you to modify them, and then get the resulting json string with the changes.

How to parse JSON using Node.js?