如何从 dynamodb 列表中删除项目

Question

• listofvalues to remove = [1,2,3]
• myList from dynamodb = [1,2,3,4,5,6,7]
• Do i need to loop every single item find the index and remove
• Is there any better approach
• Gone through link Add or remove an entry from a List type attribute in a DynamoDB table item

import boto3
dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('myowntable')
response = []
response_table = table.get_item(Key={'id': '19'})
        if 'Item' in response_table and response_table['Item']:
            response.append(response_table['Item'])

listofvalues = [1,2,3]
for i in listofvalues:
    id_index_delete = str(response[0]['myList'].index(i))
    query = "REMOVE myList[" + id_index_delete + "]"
    table.update_item(
                    Key={
                        'id': '19'
                    },
                    UpdateExpression=query
                )

Answer 1

You can remove multiple items from a list in a signle operation with an update expression like REMOVE myList[0], myList[2] . Here's one way to do it using boto3:

id = 'a1'
response_table = table.get_item(Key={'id': id})
response = response_table.get('Item', {}).get('myList', [])
listofvalues = [1,2,3] # remove these items from myList

items_to_remove = [f'myList[{response.index(x)}]' for x in listofvalues if x in response ]
query = "REMOVE " +  ", ".join(items_to_remove)

if len(items_to_remove):
  table.update_item(Key={'id': id}, UpdateExpression=query)

Answer 2

If you turn your list into a map, you can then delete items based on the map key and do all deletes in one operation.

Old: [1,2,3]

New: {“1”:1,”2”:2,”3”:3}