`createdAt` is updated as `updatedAt` when I do an upsert on my Entity

[clementmarcilhacy]

Describe the bug
I have an Entity with the attributes createdAt and updatedAt as defined in the electrodb playground:

createdAt: {
        type: "number",
        default: () => Date.now(),
        // cannot be modified after created
        readOnly: true
      },
updatedAt: {
        type: "number",
        // watch for changes to any attribute
        watch: "*",
        // set current timestamp when updated
        set: () => Date.now(),
        readOnly: true
      }

and I do an upsert on my Entity: const { data } = MyEntity.upsert(data).go() but both the createdAt and the updatedAt attributes are updated with the same Date.now() value.

It looks like the upsert method is always doing a PutItem, and then rewriting the object entirely in dynamodb.

According to the documentation, "Unlike the put method, however, upsert perform an update if that record already exists.".

ElectroDB Version
I am using version ^2.5.1

ElectroDB Playground Link

Entity/Service Definitions
Include your entity model (or a model that sufficiently recreates your issue) to help troubleshoot.

{
  model: {
    entity: "my_entity",
    service: "my_service",
    version: "my_version",
  },
  attributes: {
    prop1: {
      type: "string",
    },
    prop2: {
      type: "string",
    },
    createdAt: {
      type: "number",
      default: () => Date.now(),
      // cannot be modified after created
      readOnly: true,
    },
    updatedAt: {
      type: "number",
      // watch for changes to any attribute
      watch: "*",
      // set current timestamp when updated
      set: () => Date.now(),
      readOnly: true,
    },
  },
  indexes: {
    record: {
      pk: {
        field: "pk",
        composite: ["prop1"],
      },
      sk: {
        field: "sk",
        composite: ["prop2"],
      },
    },
  },
};

Expected behavior
createdAt not modified when doing an upsert for the second time.

Errors

Additional context

[clementmarcilhacy]

Actually, the problem seems to be with all readOnly attributes when doing an upsert (I did not test the other methods).

When doing an upsert, I expected the UpdateExpression to have a if_not_exists clause on the readOnly attributes.

I had to manually replace it in the the params sent to dynamodb:

const params = await MyEntity.upsert({prop1, prop2}).params();

params['UpdateExpression'] = params[
  'UpdateExpression'
].replace(
  '#createdAt = :createdAt_u0',
  '#createdAt = if_not_exists(#createdAt,:createdAt_u0)',
);

await MyEntity.upsert({prop1, prop2}).go({
  params,
});

[tywalch]

Hi @clementmarcilhacy 👋

This has been added to 2.7.0