Loopback-Filter parsing function needed

I'm looking for a method (or set of methods) which parse the Filter-Objects into an actual SQL query string.

Examples:

{"where": {"NEKDNR": {"inq": [93006]}}}
  => WHERE NEKDNR IN (93006)

{"where": {"or": [{"NEARTNR": {"inq": [140000]}},{"NEKDNR": 93006} ]}} 
  => WHERE NEARTNR IN (140000) OR NEKDNR = 93006

{"where":{"or":[{"and":[{"NEARTNR":{"inq":[140000]}},{"NEKDNR":93006}]},{"NEARTNR":{"inq":[20000]}}]}}
  => WHERE (NEARTNR IN 140000 AND NEKDNR = 93006) OR NEARTNR IN 20000

We have the problem, that we have requests providing Filter objects like above, but the repository has to be refactored using a specialized SQL instead of the built in find-method. But now we are unable to easily add the WHERE-part to the SQL because, it's really complicated to parse the filter object.

So, is there such a method providing the SQL from a filter object which can be required in our sourcecode?

No source file, test, or entry point is identified in the issue. Start by locating the existing Filter-object handling and determine how the shown nested where, or, and and examples should map to SQL; done means a reusable method is available for callers that need to add a filter-derived WHERE clause.