I'm developing with MongoDB and I'm creating a com...

# getting-started

[frank]

I'm developing with MongoDB and I'm creating a common class for the connection to DB.

I was having trouble implementing getCollection() generic method but I succeeded.
I'm looking for advice or alternatives to my approach.

GetCollection() Method:

inline fun <reified T> getCollection(collection: String): MongoCollection<T> {
  return database.getCollection(collection, T::class.java)
}

Full Code:

open class Connection<T> {
  constructor(){
    startMongoDB()
  }

  val client by lazy { KMongo.createClient()  }
  val database by lazy { getDB() }

  fun getDB(): MongoDatabase {
    return client.getDatabase(DB_NAME)
  }

  inline fun <reified T> getCollection(collection: String): MongoCollection<T> {
    return database.getCollection(collection, T::class.java)
  }

  private fun startMongoDB() {
    client
    database
  }
}

[Klitos Kyriacou]

Maybe there's something I don't quite understand, but what is the point of those two lazily constructed properties which you construct in the class's constructor (and therefore are not really lazy at all)?

[Stephan Schroeder]

I don't even think Connection needs to be generic or open 🤔
How about:

class Connection {
  private val client = KMongo.createClient()
  val database = client.getDatabase(DB_NAME)
}

inline fun <reified T> Connection.getCollection(collection: String): MongoCollection<T> =
    this.database.getCollection(collection, T::class.java)

and there is a point to be made that maybe the function should be called directly on Database instead of on Connection , so maybe even

inline fun <reified T> Database.getCollection(collection: String): MongoCollection<T> =
    this.getCollection(collection, T::class.java)

[frank]

but what is the point of those two lazily constructed properties which you construct in the class's constructor (and therefore are not really lazy at all)?

I don't even think Connection needs to be generic or open

Thx, for the tips.

Yes, I already had some corrected in my second revision of the code.

[frank]

My last change implementing Coroutines:

class Connection {
  private val client = KMongo.createClient().coroutine
  val database = client.getDatabase(DB_NAME)
  val session = GlobalScope.async(start = CoroutineStart.LAZY) { client.startSession() }
  
  inline fun <reified T : Any> getCollection(collection: String): CoroutineCollection<T> {
    return database.getCollection(collection)
  }
}