Dynamo Delete Item based on ConditionExpression

Question

Hi everyone,

I have been having some issues with deleting an item when pasing ConditionExpressions.
This is my params that is passed into the DeleteCommand. 
I am expecting this to delete the Item below, but everytime, I have been getting **ConditionalCheckFailedException: The conditional request failed** error.

` const input: DeleteCommandInput = {
    TableName: 'TABLE_NAME',
    ConditionExpression: 'PK = :v1 and begins_with(SK, :v2)',
    ExpressionAttributeValues: {
      ':v1': 'USER#0ee34e40-c739-4bbd-b72b-9361a54db2b5#STUDENT#111',
      ':v2': 'TEST#414fbe9f-1675-47a1-9c3d-f40cb7a25c51',
    },
    Key: {
      PK: 'USER#0ee34e40-c739-4bbd-b72b-9361a54db2b5#STUDENT#111',
      SK: 'TEST#414fbe9f-1675-47a1-9c3d-f40cb7a25c51',
    },
  };`

This is a sample of the Item that I would like to delete. As you can see, 
`PK =  "USER#0ee34e40-c739-4bbd-b72b-9361a54db2b5#STUDENT#111"`, which is an exact of PK that I am passing in as :v1 and PK above.
`SK = TEST#414fbe9f-1675-47a1-9c3d-f40cb7a25c51#DATE#1700671174102"`, which starts with what I passed in above too.

`  {
    "PK": "USER#0ee34e40-c739-4bbd-b72b-9361a54db2b5#STUDENT#111",
    "SK": "TEST#414fbe9f-1675-47a1-9c3d-f40cb7a25c51#DATE#1700671174102",
    "GSI1PK": "USER#0ee34e40-c739-4bbd-b72b-9361a54db2b5#FORM#E26",
    "GSI1SK": "TEST#414fbe9f-1675-47a1-9c3d-f40cb7a25c51#DATE#1700671174102",
    "type": "ACT",
    "id": "414fbe9f-1675-47a1-9c3d-f40cb7a25c51",
    "formId": "E26",
    "classId": "123",
    "className": "class1",
    "studentId": "111",
    "studentName": "student1",
    "userId": "0ee34e40-c739-4bbd-b72b-9361a54db2b5",
    "createdAt": "2023-09-09T23:30:50.565Z"
}`

Any one have any ideas why this is failing to match?
Love to get some suggestions.

Thank you!

Accepted Answer

Not answering the question but why use the PK and SK as the conditions? You're already supplying them as part of the DeleteItem call - you don't need to further specify them as conditions. Conditions are there so that you can specify other attributes in the record.

Answer

While it is possible to use `ConditionExpressions` with a `DeleteItem`, I believe your understanding on how it works is wrong. When using a `ConditionExpression` on a Put/Delete/Update you only evaluate the item which you are operating on, DynamoDB does not look at any other items in the table.

This is the reason why `begins_with(SK, :v2)` is giving you issues. You already know the sort key begins with that, so there is no need for the condition.

Dynamo Delete Item based on ConditionExpression

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