Kotlin Interface projections nullabillity issues

[iPave]

Hi, I'm writing an interface projection and instead of getting some readable error while initializing the result I'm getting a runtime NullPointerException on non-nullable type.

@Entity
class Customer(
    @Id
    val id: Long? = null,

    var name: String? = null,

    val age: Int
)

interface CustomerRepository : CrudRepository<Customer, Int> {


    @Query("select c.name from Customer c")
    fun customProjectionQuery(): List<NameWithAgeOnly>

}

interface NameWithAgeOnly {
    val name: String
    val age: Int
}

@Service
class Service(
    private val customerRepository: CustomerRepository
) {

    @PostConstruct
    fun test() {
        val customerWithName = Customer(id = 1, name = "John", age = 25)
        val customerWithoutName = Customer(id = 2, name = null, age = 33)
        customerRepository.save(customerWithName)
        customerRepository.save(customerWithoutName)
        val customers = customerRepository.customProjectionQuery()
        for (customer in customers) {
            println(customer.name)
        }
    }
}

Caused by: java.lang.NullPointerException: Cannot invoke "org.dev.NameWithAgeOnly.getName()" because "customer" is null

Can you please clarify what am I doing wrong. And maybe give some workaround. Isn't it a bug?
I've also tried to use kotlin dto class instead of interface, but then I'm getting

Caused by: org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [org.dev.NameWithAgeOnly]

Here is reproducible example: https://github.com/iPave/jpa-projections-issue/tree/main

[quaff]

It's caused by missing column aliases from tuple metadata, not sure Spring Data JPA could handle it, you can fix it by adding alias in your query like c.name as name.

IIRC, data class will be supported since 4.0.

BTW, you forgot c.age in your query.

[iPave]

It's caused by missing column aliases from tuple metadata, not sure Spring Data JPA could handle it, you can fix it by adding alias in your query like c.name as name.

IIRC, data class will be supported since 4.0.

BTW, you forgot c.age in your query.

@quaff Thanks for you reply, even if I add aliases jpa just puts null to notNullable property and this code

    fun test() {
        val customerWithName = Customer(id = 1, name = "John", age = 25)
        val customerWithoutName = Customer(id = 2, name = null, age = 33)
        customerRepository.save(customerWithName)
        customerRepository.save(customerWithoutName)
        val customers = customerRepository.customProjectionQuery()
        for (customer in customers) {
            println(customer.name + " " + customer.age)
        }
    }

just prints:

John 25
null 33

But it should in my opinion give some error and not initialize not nullable type with null. I've made change and pushed to the repo fix of alias, so you can reproduce it. Thanks.

[quaff]

But it should in my opinion give some error and not initialize not nullable type with null.

I'm trying to fix it by #3244.

[christophstrobl]

Thank you @iPave for reaching out.
The projecting proxy should react to the nullability constraints. Thanks @quaff for already submitting a PR.
We'll take care of it.

Regarding the DTO projection error, that will see an update with the data-jpa:3.5.0 release.

[iPave]

@quaff @christophstrobl thank you.