Spring Data JPA projections

JPA entity:

@Entity
data class Person(

    @NotBlank
    @Column(nullable = false)
    val firstName: String = "",

    @NotBlank
    @Column(nullable = false)
    val lastName: String = "",

    // other fields...
)

Projection Views (interfaces and classes are possible to use):

interface PersonFirstNameInterfaceView {
    val firstName: String
}

data class PersonFirstNameClassView(val firstName: String)

JPA Repository (not By suffix in the end of method names):

interface PersonRepository : JpaRepository<Person, Long> {
    fun getAllFirstNamesBy(): List<PersonFirstNameInterfaceView>
    fun findOloloTrololoBy(): List<PersonFirstNameClassView>
    fun findAllBy(): List<PersonFirstNameInterfaceView>
    fun findBy(): List<PersonFirstNameInterfaceView>
    fun getBy(): List<PersonFirstNameClassView>
}

Run tests:

./mvnw clean test