Improvement: Redundant ExpressionAttribute/Values

[simlu]

We noticed that this library doesn't deduplicate ExpressionAttributeNames or ExpressionAttributeValues

Example request

{
      "TableName": "...............",
      "Key": {
        "id": {
          "S": "ecf9e8ee-8518-4b7c-b3c0-4e308e9bbeaa"
        }
      },
      "UpdateExpression": "SET #slug = :slug, #inputString = :inputString, #target = :target, #type = :type, #timestamp = :timestamp",
      "ExpressionAttributeNames": {
        "#slug": "slug",
        "#inputString": "inputString",
        "#target": "target",
        "#type": "type",
        "#timestamp": "timestamp",
        "#attr1": "target",
        "#attr2": "target"
      },
      "ExpressionAttributeValues": {
        ":slug": {
          "S": "50-percent-off"
        },
        ":inputString": {
          "S": "50% off"
        },
        ":target": {
          "S": "620fa000-e1d8-4da0-9407-42814024cedb"
        },
        ":type": {
          "S": "offer"
        },
        ":timestamp": {
          "S": "2018-12-21T21:11:19.000Z"
        },
        ":attr2": {
          "S": "620fa000-e1d8-4da0-9407-42814024cedb"
        }
      },
      "ConditionExpression": "attribute_not_exists(#attr1) OR #attr2 = :attr2",
      "ReturnValues": "ALL_OLD"
    }

You can see that target exists twice. In this case, since there is not a lot of data, this is ok.

Is this something that this library should handle?

[jeremydaly]

Thanks for pointing this out, @simlu. I'm not sure this would be much of an optimization, but I will add it as an enhancement to consider.