CODEWITHSUNDEEP
pythonamazon-web-servicesamazon-dynamodbaws-lambdaboto3
sean
sean

Reputation: 3634

AWS DynamoDB Python - boto3 Key() methods not recognized (Query)

I am using Lambda (Python) to query my DynamoDB database. I am using the boto3 library, and I was able to make an "equivalent" query:

This script works:

import boto3
from boto3.dynamodb.conditions import Key, Attr
import json

def create_list(event, context):
    resource = boto3.resource('dynamodb')
    table = resource.Table('Table_Name')

    response = table.query(
        TableName='Table_Name',
        IndexName='Custom-Index-Name',
        KeyConditionExpression=Key('Number_Attribute').eq(0)
    )
    return response

However, when I change the query expression to this:

KeyConditionExpression=Key('Number_Attribute').gt(0)

I get the error:

"errorType": "ClientError",
  "errorMessage": "An error occurred (ValidationException) when calling the Query operation: Query key condition not supported"

According to this [1] resource, "gt" is a method of Key(). Does anyone know if this library has been updated, or what other methods are available other than "eq"?

[1] http://boto3.readthedocs.io/en/latest/reference/customizations/dynamodb.html#ref-dynamodb-conditions

---------EDIT----------

I also just tried the old method using:

response = client.query(
        TableName = 'Table_Name',
        IndexName='Custom_Index',
        KeyConditions = {
            'Custom_Number_Attribute':{
                'ComparisonOperator':'EQ',
                'AttributeValueList': [{'N': '0'}]
            }
        }
    )

This worked, but when I try:

response = client.query(
            TableName = 'Table_Name',
            IndexName='Custom_Index',
            KeyConditions = {
                'Custom_Number_Attribute':{
                    'ComparisonOperator':'GT',
                    'AttributeValueList': [{'N': '0'}]
                }
            }
        )

...it does not work.

Why would EQ be the only method working in these cases? I'm not sure what I'm missing in the documentation.

Upvotes: 13

Views: 22773

Answers (1)

Guy Daher
Guy Daher

Reputation: 5601

From what I think: Your Partition Key is Number_Attribute, and so you cannot do a gt when doing a query (you can do an eq and that is it.)

You can do a gt or between for your Sort Key when doing a query. It is also called Range key, and because it "smartly" puts the items next to each other, it offers the possibility of doing gt and between efficiently in a query

Now, if you want to do a between to your partition Key, then you will have to use scan like the below:

Key('Number_Attribute').gt(0)
response = table.scan(
    FilterExpression=fe
)

Keep in mind of the following concerning scan:

The scan method reads every item in the entire table, and returns all of the data in the table. You can provide an optional filter_expression, so that only the items matching your criteria are returned. However, note that the filter is only applied after the entire table has been scanned.

So in other words, it's a bit of a costly operation comparing to query. You can see an example in the documentation here.

Hope that helps!

Upvotes: 14

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