Gate: RelationOutputDto Missing `createdAt` Field

[nicoprow]

Summary

The output DTO for business partner relations (RelationOutputDto) is missing the createdAt timestamp. The standard data model defines Created At as an attribute of a Business Partner Relation. The input-stage DTO (RelationDto) already carries this field correctly; the output stage does not.

Standard Reference

CX-0074 §1.5.2.5 BUSINESS PARTNER RELATION

Attribute	Description	Type
Created At	The date and time when the business partner relation data record has been created.	Date / Time
Updated At	The date and time when the business partner relation data record has been last updated.	Date / Time

Current State

RelationOutputDto (bpdm-gate-api/.../model/RelationOutputDto.kt) only exposes updatedAt:

data class RelationOutputDto(
    val externalId: String,
    val relationType: SharableRelationType,
    val sourceBpn: String,
    val targetBpn: String,
    val validityPeriods: Collection<RelationValidityPeriodDto>,
    val reasonCode: String?,
    val updatedAt: Instant          // ← present
    // createdAt is absent          // ← missing
)

The input-stage counterpart RelationDto correctly includes both:

data class RelationDto(
    ...
    val updatedAt: Instant,
    val createdAt: Instant          // ← present on input
)

Impact

Consumers reading the output stage to reconcile or audit relation data cannot determine when a relation was originally created. This breaks symmetry with the input stage response and deviates from the standard's data model.

Proposed Fix

Add createdAt: Instant to RelationOutputDto:

data class RelationOutputDto(
    val externalId: String,
    val relationType: SharableRelationType,
    val sourceBpn: String,
    val targetBpn: String,
    val validityPeriods: Collection<RelationValidityPeriodDto>,
    val reasonCode: String?,
    val updatedAt: Instant,
    val createdAt: Instant           // ← add this
)

The underlying database entity already persists a creation timestamp (used to populate RelationDto.createdAt), so no schema migration is needed — only the mapping layer and the DTO class require updating.