How to initialize value in data class constructor kotlin

I guess you are trying to have image save the full path of some URL.

An idea to achieve this is to have a backing field into Category class like the following

@Entity(tableName = "categories")
data class Category(
    @PrimaryKey(autoGenerate = false)
    val name: String,
    var image: String,
){
   val imageUrl: String
       get() = "some Url" + image
}

Then when you want to load the image you could have

val item:Category
imgViwew.load(item.imageUrl)

You can solve this with the help of JPA lifecycle events, like this:

@Entity(tableName = "categories")
data class Category(
    @PrimaryKey(autoGenerate = false)
    val name: String,
    var image: String,
){

   @PostLoad // <---
   fun postLoad() {
     image = "someUrl" + image
   } 
}