How to convert map and nested map to string and vise versa in Kotlin?

Question

I have no idea how to convert HashMap and nested Hashmap to string and vise versa:

I use Room to save data in a local database. The "users " hashmap is a parameter of the data class. To save this parameter "users " in the Room database, we must convert it to a primitive such as string, boolen, Integer, etc. Room does not support object references, so type converters are required.

val users = HashMap<String, HashMap<String, Any>>()

    val user1 = HashMap<String, Any>()
    user1["filter"] = 0
    user1["group"] = "groupId"
    user1["labelsVisibility"] = true
    user1["sort"] = 1
    user1["view"] = 3
    users["user1"] = user1

    val user2 = HashMap<String, Any>()
    user2["filter"] = 0
    user2["group"] = "groupId"
    user2["labelsVisibility"] = true
    user2["sort"] = 1
    user2["view"] = 3
    users["user2"] = user2

Answer 1

Solution

There may be a better way to do this, but it works

1. converting a HashMap<String, HashMap<String, Any>> to a string using special symbols * + (a symbols must be unique in string)

    fun fromUsersPreferences(users: HashMap<String, HashMap<String, Any>>): String {
      var usersString = ""
      users.forEach {
        usersString = usersString.plus("${it.key}*${it.value}+")
      }
      usersString = usersString.dropLast(1)
      return usersString
    }
   

output:

"user1*{filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}+user2*{filter=1, view=1, labelsVisibility=false, sort=0, group=groupId}"

2. converting a string to a HashMap<String, HashMap<String, Any>>

   fun toUsersPreferences(users: String): HashMap<String, HashMap<String, Any>> {
    val usersMap = users.split("+").associateTo(HashMap()){
        val list = it.split("*")
        val userKey = list[0]
        val userValue = list[1].removeSurrounding("{", "}").split(", ").associateTo(HashMap()){
            val (key, value) = it.split("=")
            if (key.equals("group")) {
                Pair<String, Any>(key, value)
            } else if (key.equals("labelsVisibility")) {
                Pair<String, Any>(key, value.toBoolean())
            } else {
                Pair<String, Any>(key, value.toInt())
            }
        }
   
        Pair(userKey, userValue)
    }
   
    return usersMap
   }
   

output:

{user1={filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}, user2={filter=1, view=1, labelsVisibility=false, sort=0, group=groupId}}