Production Architectural Blueprint

SAP RAP Concurrency Control, Draft Locking & ETag Guide

Framework: RESTful Application Programming Model (RAP) Standard: Optimistic & Pessimistic Concurrency Clean Core Tier: Tier-1 On-Stack

1. The Concurrency Dilemma in Stateless Web Applications

In classic SAP GUI transactions, when User A entered transaction VA02, the system acquired an exclusive SAP Enqueue lock on the sales order table. Any other user attempting to open the same order received an immediate lock error: "Document is locked by User A".

In modern SAP Fiori and web-based applications, HTTP connections are stateless. Holding database connections or permanent exclusive locks while a user has a browser tab open is architecturally infeasible. However, without concurrency control, the Lost Update Problem emerges: User A and User B open the same record simultaneously; User B saves first, and User A unwittingly overwrites User B's edits.

2. Dual-Layer Concurrency in SAP RAP

SAP RAP resolves this using an innovative two-layer architecture combining Optimistic Concurrency (ETags) and Pessimistic Draft Locking (Enqueue Integration):

Concurrency Layer	Mechanism	When Evaluated	Clean Core Responsibility
1. Master ETag (Local)	HTTP If-Match header with timestamp hash	On every single CUD operation (Active & Draft)	Guarantees atomic row consistency between client and server
2. Total ETag (Root)	Root entity timestamp (lastChangedAt)	During Draft Activate action	Ensures active entity was not modified out-of-band by another user/job
3. Draft Enqueue Lock	SAP Enqueue Server exclusive lock	When user enters Edit mode on Draft	Prevents two users from simultaneously drafting the same active record

3. The Architecture of Total ETag vs Master ETag

4. Behavior Definition (BDEF) Configuration Blueprint

managed implementation in class zbp_r_salesorder unique;
strict ( 2 );
with draft;

define behavior for ZR_SalesOrder alias Order
persistent table zt_order_hdr
draft table zt_order_hdr_d
lock master total etag LastChangedAt
authorization master ( global, instance )
etag master LocalLastChangedAt
{
  create;
  update;
  delete;
  association _Items { create; with draft; }

  draft action Edit;
  draft action Activate optimized;
  draft action Discard;
  draft action Resume;
  draft determine action Prepare;
}

define behavior for ZR_SalesOrderItem alias OrderItem
persistent table zt_order_itm
draft table zt_order_itm_d
lock dependent by _Order
authorization dependent by _Order
etag master LocalLastChangedAt
{
  update;
  delete;
  association _Order { with draft; }
}

5. Resolving HTTP 412 Precondition Failed in Fiori Elements

When an OData V4 client receives 412 Precondition Failed, it indicates the client supplied an outdated ETag in the If-Match header. In SAP Fiori Elements apps:

• Ensure the OData V4 entity set specifies the ETag field in the metadata document (@Core.OptimisticConcurrency).
• Verify that side effects or background actions refresh the client cache using ETag: W/"..." response headers.
• Never modify timestamps manually in custom determination logic; rely exclusively on the RAP managed runtime automatic timestamp update.