在嵌套的 DynamoDB 字典上动态和有条件地 update_item

Question

I have a DynamoDB table with items in the following format:

{
  "attributes": {
    "cities": {
      "oakland": {
        "data": "Some stuff."
      }
    },
    "people": {
      "Joe": {
        "data": "Some stuff."
      }
    }
}

I have a JSON file (dynamodbupdate.json) that contains the new data I would like to add. The structure looks like this:

{
  "attributes": {
    "cities": {
      "oakland": {
        "data_point_1": "warm"
      }
    },
    "people": {
      "Joe": {
        "data_point_1": "tall",
        "data_point_1": "smart"
      }
    }
}

I would like to update the table using the update_item action from the boto3 library to add new data to my table without overwriting the existing data. I can perform this with a single table item, but I'm trying to find a way to dynamically add new data to several items so that my new table will look like this:

{
  "attributes": {
    "cities": {
      "oakland": {
        "data": "Some stuff.",
        "data_point_1": "warm"
      }
    },
    "people": {
      "Joe": {
        "data": "Some stuff."
        "data_point_1": "tall",
        "data_point_2": "smart"
      }
    }
}

The UpdateExpression for doing this to a single item would look something like this:

UpdateExpression = 'SET people.Joe.data_point_1 = if_not_exists(people.Joe.data_point_1, tall)'

However, I would love to find a way to iterate through the entire contents of the dynamodbupdate.json file and issue an an update_item command for all data.

This post comes pretty close to what I need, but I can't wrap my head around the proper way to do it in my example. Thanks for your help!

Answer 1

I was able to (mostly) figure this out by doing the following:

def lambda_handler(event, context):
    configPath = os.environ['LAMBDA_TASK_ROOT'] + "/dynamodbupdate.json"
    configContents = open(configPath).read()
    configJson = json.loads(configContents)
    ld = configJson.get('attributes').get('cities')
    cities_dict = (list(ld))
    for x in cities_dict:
        all_dp = list(ld.get(x))
        for dp in all_dp:
            update_query = 'SET #a.#c.#x.#dp = if_not_exists(#a.#c.#x.#dp, :val)'
            perform_update = table.update_item(
                Key={'primarykey': whateveryourkeyis},
                ExpressionAttributeValues={
                    ':val': ld.get(x).get(dp)
                },
                ExpressionAttributeNames={
                    '#a': 'attributes',
                    '#c': 'cities',
                    '#x': x,
                    '#dp': dp
                },
                UpdateExpression=update_query)

I can just loop through the cities/people level and pull that data in, as well. Hope this helps someone!