DynamoDB filter if primary key contains value

Question

CURRENTLY

I have a table in DynamoDB with a single attribute - Primary Key - that contains unique values.

PK
------
#A#B#C#
#B#C#
#C#D#E#
#BC#

ISSUE

I am looking to do 2 searches for #B#C# (1) exact match, and (2) containing match, and therefore only want results:

(1) Exact Match:
#B#C#

(2) Containing Match:
#A#B#C#
#B#C#

Are these 2 searches possible against the primary key?
If so, what is the most efficient query to run? e.g. QUERY or SCAN

Note:

For (2) I am using the following code, but it is returning all items in DB:

            params = {
                TableName: 'myTable',
                FilterExpression: "contains(#key, :v)",
                ExpressionAttributeNames: { "#key": "PK" },
                ExpressionAttributeValues: { ":v": #B#C# }
            }

            dynamodb.scan(params,callback)

Seth Geoghegan Seth Geoghegan · Accepted Answer · 2020-10-18T16:10:57

DynamoDB supports two main types of searches: query and scan. The Query operation finds items based on primary key values. The Scan operation returns one or more items and item attributes by accessing every item in a table or a secondary index

If you wanted to find the item with a primary key #B#C, you would use the query API:

ddbClient.query(
  {
    "TableName": "<YOUR TABLE NAME>",
    "KeyConditionExpression": "#pk = :pk",
    "ExpressionAttributeValues": {
      ":pk": {
        "S": "#B#C"
      }
    },
    "ExpressionAttributeNames": {
      "#pk": "PK"
    }
  }
)

For your second access pattern, you'll need to use the scan API because you are searching across the entire table/secondary index.

You can use scan to test if a primary key has a substring using contains. I don't see anything wrong with the format of your scan operation.

Be careful when using scan this way. Because scan will read your entire table to fetch results, you will have a fairly inefficient operation at scale. If this operation is run infrequently, or you are running it against a sparse index, it's probably fine. However, if it's one of your primary access patterns, you may want to reconsider using the scan API for this operation.

DynamoDB filter if primary key contains value

1 Answers