OData Gateway Part 6: GET_ENTITY and Key Handling

📌 KEY POINTS
✅ GET_ENTITY answers /EntitySet(key) — one record. Keys arrive in it_key_tab as name/value pairs (strings) and via io_tech_request_context->get_converted_keys.
✅ SAP keys often have leading zeros (VBELN, KUNNR, MATNR); convert with CONVERSION_EXIT_ALPHA_INPUT before selecting, or the record is "not found".
✅ If the entity does not exist, raise /IWBEP/CX_MGW_BUSI_EXCEPTION with textid resource_not_found — the client receives HTTP 404, not an empty 200.
⚠️ Fiori object pages call GET_ENTITY after navigation from the list. A key that works in the list but not in GET_ENTITY is the most common "object page empty" bug.

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▶ WHERE WE ARE
Part 5 made the service reachable. Now the single read that every object page uses.

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▶ 1. KEY INPUT

• URL: /SalesOrderSet('0000004711') — single key.
• Composite: /SalesOrderItemSet(SalesOrder='0000004711',SalesOrderItem='000010').
• it_key_tab: table of name/value (external property names, values as strings).
• io_tech_request_context->get_converted_keys( IMPORTING es_key_values = ls_entity ): values already converted into the entity structure's types.

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▶ 2. CONVERSIONS

• Leading zeros: CONVERSION_EXIT_ALPHA_INPUT for VBELN, KUNNR, LIFNR; material has its own exit (MATN1).
• Dates in keys: Edm.DateTime format in the URL (datetime'2026-01-31T00:00:00'); converted keys give the ABAP date.
• Special characters: keys are URL-encoded by the client.

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▶ 3. READ AND MAP

• SELECT SINGLE with the full key.
• Map to er_entity (type from MPC).
• Same mapping logic as GET_ENTITYSET — put it into one private method to avoid differences.

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▶ 4. NOT FOUND AND ERRORS

• Not found → RAISE EXCEPTION TYPE /iwbep/cx_mgw_busi_exception with textid resource_not_found and entity_type → HTTP 404.
• Missing key → business error with a clear message (400).

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▶ 5. AUTHORIZATION

• Check the record's authorization (e.g. V_VBAK_VKO with sales org, channel, division) — GET_ENTITY must not reveal records the list would hide.

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▶ 6. KEY TROUBLESHOOTING

• Compare $metadata key properties, list response keys and GET_ENTITY URL.
• Check that the list returns keys with the same format (leading zeros) that GET_ENTITY expects.

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▶ STEP BY STEP

1. Redefine SALESORDERSET_GET_ENTITY.
2. Read the key, apply ALPHA conversion, SELECT SINGLE.
3. Raise resource_not_found when sy-subrc <> 0.
4. Add AUTHORITY-CHECK on V_VBAK_VKO.
5. Test with '4711' and '0000004711' and a non-existing number.

✅ CHECKPOINT: GET_ENTITY returns the right record for any key format, 404 when missing, and respects authorizations.

A Fiori list showed sales orders correctly, but the object page stayed empty for every order. The list returned keys without leading zeros because a CONVERSION_EXIT_ALPHA_OUTPUT had been applied during mapping; GET_ENTITY then selected VBELN = '4711', which never exists in VBAK.
The fix removed the output conversion from the key property (display formatting was left to the UI) and added ALPHA input conversion in GET_ENTITY for robustness. The team moved mapping into one shared private method used by both GET_ENTITY and GET_ENTITYSET.

• Selecting without ALPHA conversion — "not found" for valid numbers.
• Returning an empty entity with HTTP 200 instead of 404.
• Different mapping logic in GET_ENTITY and GET_ENTITYSET.
• Missing authorization check on single reads.
• Reading key names in the wrong case ('SALESORDER' vs 'SalesOrder').

• Convert keys with the proper conversion exit.
• Raise resource_not_found for missing records.
• Share mapping between list and single reads.
• Check authorization per record.
• Test with padded, unpadded and invalid keys.

Questions: "How do you read keys in GET_ENTITY?", "Object page is empty but list works — why?", "How do you return 404?"
Strong answer: it_key_tab name/value pairs or get_converted_keys; ALPHA conversion for numeric-character keys; composite keys as multiple entries. Empty object page usually means key format mismatch (leading zeros, conversion exits) between list and GET_ENTITY. 404 via /iwbep/cx_mgw_busi_exception with textid resource_not_found; plus per-record authorization checks.