code: private boolean isKnownRelation(JSONArray relations, JsonObject newRelation) {
  		// Does it have an OID? Highest priority. Avoids infinite loops
  		// between ReDBox collections pointing at each other, so strict
  		if (newRelation.containsKey("oid")) {
  			for (Object relation : relations) {
  				JsonObject json = (JsonObject) relation;
  				String knownOid = (String) json.get("oid");
  				String newOid = (String) newRelation.get("oid");
  				// Do they match?
  				if (knownOid.equals(newOid)) {
  					log.debug("Known ReDBox linkage '{}'", knownOid);
  					return true;
  				}
  			}
  			return false;
  		}
  
  		// Mint records we are less strict about and happy
  		// to allow multiple links in differing fields.
  		for (Object relation : relations) {
  			JsonObject json = (JsonObject) relation;
  
  			if (json.containsKey("identifier")) {
  				String knownId = (String) json.get("identifier");
  				String knownField = (String) json.get("field");
  				String newId = (String) newRelation.get("identifier");
  				String newField = (String) newRelation.get("field");
  				// And does the ID match?
  				if (knownId.equals(newId) && knownField.equals(newField)) {
  					return true;
  				}
  			}
  		}
  		// No match found
  		return false;
  	}
docs: Test whether the field provided is already a known relationship
  
  @param relations
  The list of current relationships
  @param field
  The cleaned field to provide some context
  @param id
  The ID of the related object
  @returns True is it is a known relationship