I need a bit of help with data modeling. I have an object with a few properties that represent the task:

class Task(
    val id: Int,
    val name: String,
    val dueDate: String,
    val priority: Int,
    ...
)

Now user can modify each of the task properties. I would like to store an activity/change log containing all of the modifications e.g: - task name changed from "oldValue" to "newValue" - task priority changed from "oldValue" to "newValue" - ... What would be the best data model to represent this data model assuming that: - every Task property has a different type - list of activities will be stored in a database - list of activities will to be serialised to JSON format (and should be easily deserialised by the API client)

But the tasks don't have access to the database (and they shouldn't) and are themselves probably stored in a Collection. I don't think you can store Delegates (in this case observable) in a Collection, can you?? 🤔 So maybe you have to implement the Observer pattern in the classic way yourself. Another thing: I'd make

Task

a data class and use less basic Types (Int, String), at least not in the domain class, the entity class (which is persisted in a database) on the other hand mustn't be a data class (since the automatically generated equals method doesn't have entity class semantics) and can use basic types. So how about

data class Task (
    val id: UUID,
    val name: String,
    val dueDate: Date,
    val priority: Priority,
    ...
)

with

Priority

either being an Enum

enum class Priority(val value: Int) {
    HIGH(1),
    MEDIUM(2),
    LOW(3)
}

or an inline class with additional validation that the int value is within valid bounds!?

@JvmInline
value class Priority(val value: Int) {
    init {
        require(value in 1..3) {"value $value out of range 1..3"}
    }
}