OData Gateway Part 5: Service Registration, $metadata and Gateway Client Testing

📌 KEY POINTS
✅ Generating runtime objects registers the service in the backend; it must also be activated on the frontend in /IWFND/MAINT_SERVICE (Add Service → system alias → package).
✅ $metadata shows what clients will see: entity types, keys, properties, navigation. Read it before coding any consumer.
✅ /IWFND/GW_CLIENT tests GET, POST, PUT, PATCH/MERGE, DELETE and $batch inside SAP, with CSRF tokens and payload templates.
⚠️ After model changes, stale metadata caches cause "property not found" errors — clean caches with /IWFND/CACHE_CLEANUP and /IWBEP/CACHE_CLEANUP.

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▶ WHERE WE ARE
Part 4 explained frontend and backend. Now we make the service reachable and test it.

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▶ 1. ACTIVATION

• /IWFND/MAINT_SERVICE → Add Service → system alias (LOCAL in embedded) → filter by technical service name (ZSALES_SRV) → Add Selected Services → package (transportable).
• This creates the frontend registration and the ICF node /sap/opu/odata/sap/ZSALES_SRV.
• Check SICF: node must be active.

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▶ 2. $METADATA

• URL: /sap/opu/odata/sap/ZSALES_SRV/$metadata
• Verify: entity sets, key properties, EDM types, lengths, navigation properties, sap:creatable/updatable flags.
• Service document (root URL) lists entity sets.

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▶ 3. GATEWAY CLIENT (/IWFND/GW_CLIENT)

• Enter request URI, choose HTTP method, execute.
• GET with $format=json for readable output.
• For POST/PUT/DELETE: first GET with header x-csrf-token: Fetch, then send the token (the client handles this automatically in most releases); "Use as Request" copies a response into the request body.
• Save test cases in the Gateway client for regression.

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▶ 4. CACHES

• Frontend and backend cache the metadata.
• After regenerating MPC: /IWBEP/CACHE_CLEANUP (backend), /IWFND/CACHE_CLEANUP (frontend), or "Cleanup Cache" in MAINT_SERVICE.

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▶ 5. AUTHORIZATION

• S_SERVICE authorization for the service on the frontend (added via PFCG with the service's TADIR entry).
• Business authorizations inside your DPC code (AUTHORITY-CHECK) or via CDS DCL.

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▶ 6. TRANSPORT

• Backend: SEGW project, MPC/DPC classes, model and service registration.
• Frontend: service registration (/IWFND/ objects) and ICF node — in the package chosen during activation. In a hub, activate or transport separately on each FES.

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▶ STEP BY STEP

1. Activate ZSALES_SRV in /IWFND/MAINT_SERVICE with the correct alias.
2. Open $metadata and verify keys and types.
3. In /IWFND/GW_CLIENT run GET SalesOrderSet?$format=json.
4. Change a property length in SEGW, regenerate, observe stale metadata, then clean caches.
5. Save the GET as a test case.

✅ CHECKPOINT: you can register, verify, test and transport a Gateway service without guesswork.

After adding a field DeliveryDate to an entity, the Fiori app failed with "Property DeliveryDate not found". The developer re-checked MPC_EXT and DPC_EXT for a day.
$metadata in the browser still showed the old model — the frontend was serving a cached version. Running /IWBEP/CACHE_CLEANUP and /IWFND/CACHE_CLEANUP (and later in each tier after transport) made the new property appear. The team added cache cleanup to the post-transport checklist and saved Gateway client test cases for every entity set.

• Generating runtime objects but never activating the service in /IWFND/MAINT_SERVICE.
• Local package ($TMP) during activation, so the registration is not transported.
• Forgetting cache cleanup after model changes.
• Testing only GET, never POST/PUT/DELETE with CSRF tokens.
• Missing S_SERVICE in the users' roles.

• Verify $metadata first after every model change.
• Activate in a transportable package; check the ICF node.
• Keep saved Gateway client test cases per entity set.
• Include cache cleanup in the transport checklist.
• Grant S_SERVICE via PFCG roles, not SAP_ALL-like shortcuts.

Questions: "How do you register an OData service?", "Service works in DEV but not in QA — what do you check?", "What is x-csrf-token?"
Strong answer: activate in /IWFND/MAINT_SERVICE with system alias and transportable package, check ICF node, verify $metadata, test in /IWFND/GW_CLIENT. In QA check registration, alias, ICF node, caches, S_SERVICE, error logs. CSRF token is fetched with GET (x-csrf-token: Fetch) and sent with modifying requests to prevent cross-site request forgery.