boto3, python: appending value to DynamoDB String Set

Question

I have an object in DynamoDB:

{ 'UserID' : 'Hank', ConnectionList : {'con1', 'con2'} }

By using boto3 in lambda functions, I would like to add 'con3' to the String Set. So far, I have been trying with the following code without success:

ddbClient = boto3.resource('dynamodb')
table = ddbClient.Table("UserInfo")
table.update_item(
    Key={
        "UserId" : 'Hank'
    },
    UpdateExpression = 
        "SET ConnectionList = list_append(ConnectionList, :i)",
    ExpressionAttributeValues = {
        ":i": { "S": "Something" }
    },
    ReturnValues="ALL_NEW"
)

However, no matter the way I try to put the information inside the String Set, it always runs error.

Incorrect operand type for operator or function; operator or function: list_append, operand type: SS", Thank you, but does not work. Tried several other sources before adding a new post on stackoverflow, so far, none of the solution provided work. — ardito.bryan
– ardito.bryan, Commented Mar 11, 2021 at 12:58
Does this answer your question? DynamoDB: list_append alternative for sets — Maurice
– Maurice, Commented Mar 11, 2021 at 13:21

Maurice · Accepted Answer · 2021-03-11 13:20:34Z

4

Since you're using the resource API, you have to use the Python data type set in your statement:

table.update_item(
    Key={
        "UserId" : 'Hank'
    },
    UpdateExpression = 
        "ADD ConnectionList :i",
    ExpressionAttributeValues = {
        ":i": {"Something"},  # needs to be a set type
    },
    ReturnValues="ALL_NEW"
)

edited Mar 11, 2021 at 13:20

answered Mar 11, 2021 at 13:14

Maurice

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4 Comments

ardito.bryan Over a year ago

It now returns: Incorrect operand type for operator or function; operator or function: list_append, operand type: SS",

Maurice Over a year ago

I suggest you take a closer look at my answer on the question I linked to earlier and try to see again if it does what you want.

Maurice Over a year ago

I've updated the code and now it's basically identical, which makes this a duplicate.

ardito.bryan Over a year ago

table.update_item( Key={ "UserId" : 'Hank' }, UpdateExpression="ADD ConnectionList :set_value", ExpressionAttributeValues={ ":set_value": {'newitem'}, # needs to be a set type } ) with this works!

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