OData Link Write Operations

Hi all,

Section 7.1.6.9, Custom Exits for OData Write Requests, of the HANA Developer Guide describes how SQLScript procedures can be registered for non-trivial write requests towards an OData service. Besides Entity Write Operations the documentation also describes the possibility of Link Write Operations. I want to apply the latter type of operations in order to create new sub-items of an items EntitySet. For this my service definition looks like this:

service namespace "namespace" {
 "namespace::v_complete_item" as "Items" keys ("DB_ID") navigates ("Item_SubItems" as "SubItems" from principal);                            
 association "Item_SubItems" principal "Items" ("DB_ID") multiplicity "1"  dependent "Items" ("DB_ID") multiplicity "*"  over "namespace::t_item_goes_into" principal ("FROM_ITEM_ID") dependent ("TO_ITEM_ID")  create using "namespace::p_item_create";
}

In line 7 I reference the procedure "namespace::p_item_create" which shall be called for Link Write Operations. For completeness, here is the procedure:

PROCEDURE "_SYS_BIC"."namespace::p_item_create" (
 IN it_principal_item NAMESPACE."namespace::ts_complete_item",
 IN it_dependent_items NAMESPACE."namespace::ts_complete_item",
 OUT ot_error NAMESPACE."namespace::ts_odata_error"
 )
 LANGUAGE SQLSCRIPT
 SQL SECURITY INVOKER 
 DEFAULT SCHEMA NAMESPACE
 AS
BEGIN
 ot_error = select 400 as http_status_code, 'invalid ID' as error_message, 'value must be >= 1000' as detail from dummy;     
END;

For now, the procedure does not do anything. It just provides the necessary parameters for a Link Write Operation (in accordance to the documentation) and produces an error message, so that I can see whether the procedure was called or not. There is no problem during the activation of this code.

I tried to trigger the execution of "namespace::p_item_create" by a POST request on the Navigation Property, which uses the association:

POST http://<system>:8000/<path>/service.xsodata/Items(1)/SubItems

However, every time I try this I get the following error message from the service:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>  <error       xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">      <code/>      <message xml:lang="en-US">The URI is not valid for POST operation. The URI must point to an entity set for POST operations.</message>  </error>  

Is there something wrong with the request? Is it not possible to trigger the Link Write Operation by using the Navigation Property? If yes, how can the operation be triggered by a client request? Which resource of the service has to be used?

I hope you can help me with that. Unfortunately, the documentation does not provide any details about that.

Thanks a million!

Best regards,

René

PS: I've already posted a similar question as response to an already solved question, but got no response so far. That's why I wanted to make my question a little bit more prominent and provide additional information.