kandra-koin

kandra-koin bridges Kandra's KandraRepository<T>/KandraSuspendRepository<T> into a Koin container. It has exactly one public entry point, Application.kandraKoin(), which auto-wires one repository pair per entity already registered with kandra-core's SchemaRegistry.

Why this exists as a separate module

Wiring Kandra repositories into Koin is entirely optional — kandra-runtime's KandraRuntime.repository<T>()/suspendRepository<T>() work without any DI framework at all, and plenty of Kandra apps call those directly. kandra-koin exists so that a Koin-based app doesn't have to hand-write single { KandraRepository(session, schema, User::class, batchEngine) } boilerplate for every entity, with the qualifier-naming convention decided once, in this module, instead of reinvented per project. It depends on kandra-core, kandra-runtime, and kandra-ktor (implementation, not api — a consumer of kandra-koin doesn't automatically get kandra-ktor's symbols visible without also declaring it) plus Koin itself (implementation(libs.koin.ktor)/implementation(libs.koin.core)) — nothing else in Kandra depends on Koin, so choosing kandra-koin over kandra-kodein (or neither) never pulls Koin's classes into an app that doesn't want them.

Application.kandraKoin()

@Suppress("OPT_IN_USAGE")
fun Application.kandraKoin()

Iterates SchemaRegistry.all() and, for each entity, binds two single bindings with named qualifiers (not generic-type-only lookups — Koin can't distinguish KandraRepository<User> from KandraRepository<Wallet> at runtime due to type erasure, so the qualifier is mandatory, not optional):

For an entity User, the qualifiers are exactly "UserRepo" and "UserSuspendRepo". Both bindings construct the repository with the plugin's own CqlSession and — critically — the same BatchEngine instance as the installed Kandra plugin, so Koin-resolved repositories share the plugin's shutdown-drain guard and in-flight query counter, not an independent lifecycle.

import io.kandra.ktor.Kandra
import io.kandra.koin.kandraKoin
import org.koin.core.qualifier.named
import org.koin.ktor.ext.inject
import org.koin.ktor.plugin.Koin
 
fun Application.module() {
    install(Koin) { /* your own app-level modules, if any */ }
 
    install(Kandra) {
        contactPoints = "localhost:9042"
        keyspace = "coinx"
        localDatacenter = "datacenter1"
        register(User::class, Wallet::class)
    }
 
    kandraKoin()   // after both install(Koin) and install(Kandra) —
                   // binds "UserRepo", "WalletRepo", "UserSuspendRepo", "WalletSuspendRepo"
 
    routing {
        get("/users/{id}") {
            val repo: KandraSuspendRepository<*> by inject(qualifier = named("UserSuspendRepo"))
            @Suppress("UNCHECKED_CAST")
            val userRepo = repo as KandraSuspendRepository<User>
            val user = userRepo.findById(call.parameters["id"]!!)
            call.respond(user ?: HttpStatusCode.NotFound)
        }
    }
}

Outside an Application receiver — a plain service class — the same lookup works via KoinComponent:

class UserService : KoinComponent {
    private val userRepo: KandraSuspendRepository<*> by inject(named("UserSuspendRepo"))
 
    suspend fun getUser(id: String): User? {
        @Suppress("UNCHECKED_CAST")
        return (userRepo as KandraSuspendRepository<User>).findById(id)
    }
}

If an entity class has no simpleName (an anonymous class — not a realistic scenario for a @ScyllaTable entity, but checked anyway), kandraKoin() throws KandraException.

Full API reference

Where this shows up elsewhere on this site

• /getting-started and /tutorial/04-plugin-install — kandraKoin() in a working app.
• /modules/kandra-kodein — the same pattern for Kodein, including the standalone binder Koin doesn't have.