R2dbcEntityTemplate.upsert() generates invalid SQL for entities with @Embedded.Empty composite primary keys

[czp3009]

Summary

R2dbcEntityTemplate.upsert() generates an invalid DO UPDATE SET clause when the entity uses @Embedded.Empty for a composite primary key. The Kotlin property name of the embedded field (e.g. id) leaks into the SQL as a column name, even though it is not a real database column. PostgreSQL rejects the query with column excluded.id does not exist.

Steps to Reproduce

1. Define an entity with a composite primary key via @Id @Embedded.Empty:

@Table("entity")
data class Entity(
    @Id @Embedded.Empty
    val id: EntityId,
    val name: String,
) {
    data class EntityId(val col1: String, val col2: String)
}

2. Corresponding table:

CREATE TABLE entity (
    col1  VARCHAR(255) NOT NULL,
    col2  VARCHAR(255) NOT NULL,
    name  VARCHAR(255) NOT NULL,
    PRIMARY KEY (col1, col2)
)

3. Call template.upsert(entity)

Expected Behavior

INSERT INTO "entity" ("col1", "col2", "name")
VALUES ($1, $2, $3)
ON CONFLICT ("col1", "col2")
DO UPDATE SET "name" = EXCLUDED."name"

Only non-PK columns appear in DO UPDATE SET.

Actual Behavior

INSERT INTO "entity" ("col1", "col2", "name")
VALUES ($1, $2, $3)
ON CONFLICT ("col1", "col2")
DO UPDATE SET "id" = EXCLUDED."id", "name" = EXCLUDED."name"

PostgreSQL error:

column excluded.id does not exist

The embedded property name id is included in DO UPDATE SET, but id is not a real database column — the actual PK columns are col1 and col2.

Minimal Reproduction

https://github.com/czp3009/r2dbc-upsert-embedded-key-issue-reproduction

[leewoo97]

I opened #2331 with a fix for this issue.

The change derives upsert update columns from the mapped OutboundRow columns and excludes identifier and insert-only columns, so embedded id property names are not rendered in DO UPDATE SET.