DynamoDb Query and Append item to nested list inside a list, Python Boto3

Question

I have this kind of entity in a dynamodb table:

{
   "fieldAA":152,
   "Big_List":[
      {
         "fieldA":"value",
         "Nested_List":[
            {
               "date":"29/09/2022"
            },
            {
               "date":"06/10/2022"
            },
            {
               "date":"04/11/2022"
            },
            {
               "date":"08/11/2022"
            }
         ]
      }
   ]
}

1. How do I query(by entity id) the table in order to get the first date in the Nested_List? I have to do some comparison with the first date in the list

2.How to append a new date to the Nested_List?

Answer 1

You haven't provided much information, but this should be what you need.

How do I query(by entity id) the table in order to get the first date in the Nested_List? I have to do some comparison with the first date in the list

import boto3

table_name = "test"
dynamodb = boto3.client('dynamodb')
table = dynamodb.Table(table_name)

try:
    response = table.get_item(
        Key={
            'entity_id': '1235'
        },
        ProjectionExpression='#b.#n[0]',
        ExpressionAttributeNames={
            '#b': 'Big_List',
            '#n': 'Nested_List'
        }
    )

except Exception as e:
    print(e)

How to append a new date to the Nested_List?

date = [{"date": "08/09/2023"}]

try:
    table.update_item(
        Key={
            'entity_id': '1235'
        },
        UpdateExpression="SET #b.#n = list_append(#b.#n, :date)",
        ExpressionAttributeValues={":date": date},
        ExpressionAttributeNames={
            '#b': 'Big_List',
            '#n': 'Nested_List'
        }
    )
except Exception as e:
    print(e)