How to update a nested item in AWS DynamoDB with CLI - amazon-web-services

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.