I'm attempting to use Kotlinx Serialization with K...

# kmongo

[Mark Vogel]

I'm attempting to use Kotlinx Serialization with KMongo and I can't seem to get the serialization to work properly; It does insert the data, but completely ignores all of the Kotlinx annotations.
I see that, on the KMongo Website I'm supposed to create a custom Json configuration, but I can't seem to find any mention of where to use that Json configuration.

The closest I see is the reference to registerModule and registerSerializer, but I can't find those functions anywhere either.
I've included a screenshot of all the dependencies I have. Note these are all from:

implementation("org.litote.kmongo:kmongo-id-serialization:$kMongoVersion")
implementation("org.litote.kmongo:kmongo-coroutine-serialization:$kMongoVersion")

If someone could point me in the right direction I would appreciate it very much! 🙂

[CLOVIS]

Hi! You don't need to create a custom Json configuration. If you're happy with the defaults (and I have not had an issue with them so far), you don't have to do anything.

[CLOVIS]

Do you apply the serialization plugin to your module?

[CLOVIS]

Here's an example of the working setup for KMongo with Coroutines and Serialization: https://gitlab.com/opensavvy/formulaide/-/blob/main/mongo/build.gradle.kts

[CLOVIS]

The essential parts are:

plugins {
    kotlin("jvm")

    // Enable the serialization plugin (generates the serializers from @Serializable)
    kotlin("plugin.serialization")
}

dependencies {
    // Coroutines
   
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:<insert version here>")

    // KMongo with coroutines + serialization support
    implementation("org.litote.kmongo:kmongo-coroutine-serialization:<version here>")
}

This is all you need

[Mark Vogel]

@CLOVIS looks like I didn't have the kotlinx-coroutines-core which is essential, but doesn't throw errors. Thank you very much!

I have a couple other random questions that you may know the answers to:
1. Do you know how to use a custom Json configuration if I have the need?
2. Is it correct to do a val id: UUID directly as _id or should it be val id: Id<UUID>?

[CLOVIS]

1. I do not, but I've been using KMongo for the past 2 years in production and have not needed it, so I believe it's only useful in very rare cases. I believe the likelihood that you're doing something wrong is higher than the likelihood to need it.
2. Id<UUID> is a MongoDB ID (e.g. 580f18a2c47a16a1d0b94a80), the type parameter does nothing in MongoDB (it's just here to help you remember what corresponds to what, see my example below); UUID stores the UUID directly in the database. Which one you want depends on what you want to do. For primary keys, it's recommended to use Id<YourType> (that's what MongoDB is built for). Don't forget to add @SerialName to your primary key!

@Serializable
class Foo {
    @SerialName("_id") val id: Id<Foo>, // ID to itself
    val name: String,
    val bar: Id<Bar>, // ID to the other class
}

The type parameter in bar does nothing, it's just here to help you remember which is which, you could write Id<Nothing> everywhere and it would change nothing (though I don't recommend doing that, it's good to clarify)

[Mark Vogel]

I see that makes sense. Thanks for the info!

[Mark Vogel]

So I tested this out a bit and turns out you do need to do @Contextual @SerialName("_id") val id: UUID directly rather than using Id<UUID>. If you use Id<UUID> then it generates an ObjectId instead. I think this is like you said that it completely ignores the type parameter.

I'm not sure if I did something wrong and that I am supposed to still use Id<..>, but it seems to work with the direct UUID type.