How do I filter a collection for a null foreign key or object relation in BackAnd?

Question

I'd like to filter a collection for a null foreign key or object relation in BackAnd.

filter = [ 
  {
    "fieldName": "Parent",
    "operator": "empty",    
    "value": ""
  }
]

Here's my table/object definition:

{
  "name": "Tree",
  "fields": {
    "Title": {
      "type": "string"
    },
    "Description": {
      "type": "string"
    },
    "Parent": {
      "object": "Certifications"
    },
    "Children": {
      "collection": "Certifications",
      "via": "Parent"
    }
  }
}

When I try the filter above, I get this error:

The field "FK_Tree_Tree_Parent" is a relation field. 
To filter relation fields please use the operator "in"

This just returns all of the values in the table:

filter = [ 
  {
    "fieldName": "Parent",
    "operator": "in",    
    "value": ""
  }
]

Is it possible to get back the records that don't have a parent assigned to them?

Answer 1

You can use Queries, with the following sql

SELECT * FROM Tree WHERE Parent IS NULL