Type-safe Kotlin query extension like mongo template

[jurogrammer]

I would like to perform type-safe queries using R2dbcTemplate. My goal is to achieve functionality similar to MongoDB's template, as you suggested—reference test code.

However, there’s an issue with handling column names, as described in this issue. I’m considering a default strategy for resolving column names, though this might limit the flexibility of custom column name strategies, similar to MongoDB’s template, which only considers property names.

Are there any considerations I should keep in mind?

extension

import org.springframework.data.relational.core.query.Criteria
import org.springframework.data.relational.core.query.Criteria.CriteriaStep
import org.springframework.data.util.ParsingUtils
import kotlin.reflect.KProperty


fun where(key: KProperty<*>): CriteriaStep = Criteria.where(key.toColumn())
internal fun KProperty<*>.toColumn(): String = ParsingUtils.reconcatenateCamelCase(this.name, "_")

test

Since CriteriaBuilder doesn't override equals, I'm using toString for comparison.

import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.data.relational.core.query.Criteria

class CriteriaExtensionsKtTest {

    @Test
    fun `where(KProperty) should equal Criteria where()`() {
        val typedCriteria = where(Customer::firstName).`is`("John").toString()
        val classicCriteria = Criteria.where("first_name").`is`("John").toString()

        assertThat(typedCriteria).isEqualTo(classicCriteria)
    }


    class Customer(val firstName: String, val lastName: String)
}

[mp911de]

This is a duplicate of #1491. The comment about column names is misleading. Spring's API works primarily with property names (KProperty maps to property names as well). Having a Criteria object that is being mapped against the domain model removes the need in a Kotlin extension to resolve column names.

I suggest that you file a Pull Request and use MongoDB's implementation as inspiration for the Relational implementation.

Therefore, I'm closing this ticket as a duplicate. Happy to continue the discussion over an actual PR.

[jurogrammer]

thank you for your help!👍