I need to parse the list of `data class` into a `j...

# ktor

[Kalpesh Chandora]

I need to parse the list of data class into a json array while sending the response. I am converting the model’s content to JsonObject and then adding the object to JsonArray. Can someone please suggest a better approach?

@Serializable
data class MyModel(
    val name: String,
    val number: String
)

val list = arrayListOf<MyModel>()
repeat(5) {
    list.add(
        MyModel(
            name = UUID.randomUUID().toString(),
            number = UUID.randomUUID().toString()
        )
    )
}

val jsonArray = buildJsonArray {
    list.forEach {
        val obj = buildJsonObject {
            put("name", it.name)
            put("number", it.number)
        }
        add(obj)
    }
}

call.respond(buildJsonObject {
    put("pageSize", 10)
    put("list", jsonArray)
})

[Aleksei Tirman [JB]]

You can just respond with a list of your objects:

val list = mutableListOf<MyModel>()
repeat(5) {
    list.add(
        MyModel(
            name = UUID.randomUUID().toString(),
            number = UUID.randomUUID().toString()
        )
    )
}

call.respond(list)

[Kalpesh Chandora]

Yes, for sending a JsonArray we can directly use call.respond(list). But can you please help with when we need to send a JsonObject with JsonArray as mentioned in the above snippet

[Aleksei Tirman [JB]]

Sorry, I don't understand your question. Can you please rephrase it?

[Kalpesh Chandora]

I am trying to serve a paginated request which will respond a JsonObject

{
    "key" : "some_key",
    "pageSize" : 10,
    "notifications" : [
        // notifications list
    ]
}

I have a data class NotificationDto. I need to send List<NotificationDto> as notifications array in my response but I couldn’t find any method to directly convert my model list into JsonArray.
To achieve the similar results for another API, I have done this:

val jsonArray = buildJsonArray {
    users.forEach {
        val obj = buildJsonObject {
            put("userId", it.userId)
            put("name", it.name)
            put("photoUrl", it.photoUrl)
            put("username", it.username)
            put("isFollowedBySelf", followings[it.userId].isTrue())
        }
        add(obj)
    }
}
respond(buildJsonObject {
    put("key", nextKey)
    put("pageSize", jsonArray.size)
    put("users", jsonArray)
})

In the above code, I have manually created the fields and adding them to the JsonArray.

How can we send a List of data class without converting each field manually?

This is the code I am trying with:

val notificationsDtoList = mutableListOf<NotificationDto>()
notifications.forEach {
    notificationsDtoList.add(
        NotificationDto(
            userId = it.actionTakenBy,
            type = it.type,
            postId = it.postId,
            postImageUrl = it.postImageUrl,
            timeStamp = it.timeStamp,
            username = usersMap[it.actionTakenBy]?.username,
            photoUrl = usersMap[it.actionTakenBy]?.photoUrl
        )
    )
}
val nextKey = if (notifications.size == pageSize) {
    notifications[pageSize - 1].timeStamp
} else -1

call.respond(buildJsonObject {
    put("key", nextKey)
    put("pageSize", notifications.size)
    putJsonArray("notifications", notificationsDtoList) // Compilation error here because notificationsDtoList is not a JsonArray
})

This is the result I need to achieve:

{
  "key": "some_key",
  "pageSize": 10,
  "notifications": [
    {
      "userId": "abcde",
      "type": "type",
      "postId": "postId",
      "postImageUrl": "postImageUrl",
      "timeStamp": "timeStamp",
      "username": "username",
      "photoUrl": "photoUrl"
    }
  ]
}

[Kalpesh Chandora]

One workaround to this is creating a dedicated data class to send the response:

@Serializable
data class NotificationDtoResponse(
    val key: Long,
    val pageSize: Int,
    val notifications: List<NotificationDto>
)

call.respond(
    NotificationDtoResponse(
        pageSize = 10,
        key = System.currentTimeMillis(),
        notifications = notificationsDtoList
    )
)

Not sure, it’s the correct way to do it

[Aleksei Tirman [JB]]

This is actually not a workaround but the recommended way to do it.

[Kalpesh Chandora]

Okay, thanks a lot for helping 😇