Filtering requests

[anschl]

I'm trying to use the filter feature present in some EDC calls, e.g.:

• /v2/catalog/request
• /v2/transferprocesses/request

Even though I didn't find documentation about the filter feature I derived its structure from creating Contract Definitions:

{
  ...
  "filterExpression": [
    {
      "@type": "Criterion",
      "operandLeft": "id",
      "operator": "=",
      "operandRight": "1"
    }
  ]
}

While I got it working for some calls, I have two questions regarding them:

1. Is it possible to filter a deep property? Something like odrl:hasPolicy.id = "MQ...."
2. Is there documentation about which filter operations are available?
3. How can I find out which properties I can filter by? I'm interested in filtering by assetId in /v2/transferprocesses/request, but it says Error validating schema: Field assetId not found on type class org.eclipse.edc.connector.transfer.spi.types.TransferProcess, even though the source mentions it.