如何使用 Boto3 在 Dynamodb 上将项目添加到 string_set

Question

I have read the official AWS docs and several forums, still I cant find what I am doing wrong while adding item to string_set using Python/Boto3 and Dynamodb. Here is my code:

table.update_item(
                Key={
                    ATT_USER_USERID: event[ATT_USER_USERID]
                },
                UpdateExpression="add " + key + " :val0" , 
                ExpressionAttributeValues = {":val0" : set(["example_item"]) },
            )

The error I am getting is:

An error occurred (ValidationException) when calling the UpdateItem operation: An operand in the update expression has an incorrect data type\\"

Answer 1

It looks like you figured out a method for yourself, but for others who come here looking for an answer:

1. Your 'Key' syntax needs a data type (like 'S' or 'N')
2. You need to use "SS" as the data type in ExpressionAttributeValues , and
3. You don't need "set" in your ExpressionAttributeValues .

Here's an example I just ran (I had an existing set, test_set, with 4 existing values, and I'm adding a 5th, the string 'five'):

import boto3
db = boto3.client("dynamodb")
db.update_item(TableName=TABLE,
               Key={'id':{'S':'test_id'}},
               UpdateExpression="ADD test_set :element",
               ExpressionAttributeValues={":element":{"SS":['five']}})

So before, the string set looked like ['one','two','three','four'] , and after, it looked like ['one','two','three','four','five']

Answer 2

Building off of @joe_stech's answer, you can now do it without having to define the type.

An example is:

import boto3


class StringSetTable:
    def __init__(self) -> None:
        dynamodb = boto3.resource("dynamodb")
        self.dynamodb_table = dynamodb.Table("NAME_OF_TABLE")

    def get_str_set(self, key: str) -> typing.Optional[typing.Set[str]]:
        response = self.dynamodb_table.get_item(
            Key={KEY_NAME: key}, ConsistentRead=True
        )

        r = response.get("Item")
        if r is None:
            print("No set stored")
            return None
        else:
            s = r["string_set"]
            s.remove("EMPTY_IF_ONLY_THIS")
            return s

    def add_to_set(self, key: str, str_set: typing.Set[str]) -> None:
        new_str_set = str_set.copy()
        new_str_set.add("EMPTY_IF_ONLY_THIS")

        self.dynamodb_table.update_item(
            Key={KEY_NAME: key},
            UpdateExpression="ADD string_set :elements",
            ExpressionAttributeValues={":elements": new_str_set},
        )