How to update a nested item in AWS DynamoDB with CLI

Question

In one of my AWS DynamoDB tables I have several items that require an update within in a pipeline. The following json shows an item in the AWS DynamoDB table:

{
  "DeploymentConfigs": {
    "L": [
      {
        "M": {
          "Config": {
            "M": {
              "Name": {
                "S": "batch-komo"
              },
              "Replicas": {
                "N": "3"
              }
            }
          }
        }
      },
      {
        "M": {
          "Config": {
            "M": {
              "Name": {
                "S": "online-komo"
              },
              "Replicas": {
                "N": "3"
              }
            }
          }
        }
      }
    ]
  },
  "environment": {
    "S": "komo-claimcenter"
  }
}

How can update an object in DeploymentConfigs? Primary partition key is environment.

E.g. the object

{
        "M": {
          "Config": {
            "M": {
              "Name": {
                "S": "batch-komo"
              },
              "Replicas": {
                "N": "3"
              }
            }
          }
        }
}

shall be updated to

   {
        "M": {
          "Config": {
            "M": {
              "Name": {
                "S": "batch-komo"
              },
              "Replicas": {
                "N": "5"
              }
            }
          }
        }
 }

I do not know to achieve in the AWS CLI.

Answer 1

To update a nested part inside an item, you use an UpdateExpression with an attribute path. For example, SET DeploymentConfigs[0].Config.Replicas = :val.

The problem, however, is that your top-level attribute DeploymentConfigs is a list, so to modify one of its items, you need to know in index (in this example 0). If you don't know the index you have a problem - there is no way to "modify the list item which has name='batch-komo'" or something like that... If you need to do something like this, you have to read the entire top-level attribute, modify it in the client, and write it (or just the small change, now that you know the index) back.