MappingException when calling a modifying query method that returns kotlin.Unit

[ada-waffles]

Modifying queries can be declared as returning Void if the result count information is not needed, as shown here. The equivalent declaration in Kotlin would be to use Unit. Currently, Spring Data R2DBC does not recognize the Unit type and attempts to convert the affected row count to Unit as if it were a projection, resulting in:

org.springframework.data.mapping.MappingException: Couldn't find PersistentEntity for type class java.lang.Integer!

An example repository method that is affected:

/** Deletes the association from [userId] to [associatedUserId], if it exists */
@Modifying
@Query("DELETE FROM user_association WHERE user_id = :userId AND associated_user_id = :associatedUserId")
suspend fun deleteUserAssociation(userId: Int, associatedUserId: Int)

A workaround is to simply use the Java Void type:

/** Deletes the association from [userId] to [associatedUserId], if it exists */
@Modifying
@Query("DELETE FROM user_association WHERE user_id = :userId AND associated_user_id = :associatedUserId")
suspend fun deleteUserAssociation(userId: Int, associatedUserId: Int): Void

I believe I've tracked this down to AbstractR2dbcQuery#getExecutionToWrap and plan to attempt a PR.

[mp911de]

Thanks for reporting the issue. Returning Unit should be no different from Void handling. We probably need some changes in Spring Data Commons to consider Unit also a primitive type.

[mp911de]

I filed DATACMNS-1779 to provide void type detection. Looking at the pull request, we can simplify it by quite a bit.