Match string to object property - kotlin

Question

I have a set of policies that I want to match a request. If the policy exists, I want to match the request and see if the value matches.
The policies are List<Policies> -> (key: String, value: String) and the request can contain different keys.
Example:
The policies are a set of rules that the request should match.
class Policy {
val key: String,
val value: String
}
The request is a data class that contains different values (all optional), for example surname, firstName, address, ++++
data class Request (
id: Long = 12,
firstName: String = "test",
surname: String = "test",
address: String = "somewhere"
...// more fields
)
The list of policies can look like this (List):
List<Policy> => [
{
key: "surname",
value: "test"
},
{
key: "firstName",
value: "test"
}
]
I don't know how I can match the policies with the request. The Policy.key is a String and the Request can contain all different variations of properties.
How do I match the List of policies with my data class Request?

Answer 1

For your puroposes you need use reflection (you want to find field by name and get value), or change something in your model.
Solution with reflection can be like following:
data class Policy(
val key: String,
val value: String?
)
data class Request(
val id: Int,
val firstName: String? = null,
val surname: String? = null,
val address: String? = null
)
class PolicyException : Exception()
fun checkPolicies(request: Request, policies: List<Policy>) {
policies.forEach { policy ->
val member = request::class.members.find { member -> member.name == policy.key }
val requestMemberValue = member?.call(request)
if (requestMemberValue != policy.value) throw PolicyException()
}
}
fun main(args: Array<String>) {
println("Hello, reflection!")
checkPolicies(Request(id = 0, firstName = "Johnn"), listOf(Policy("firstName", "John")))
}
Also, I changed your policy model to handle nullable values (and still handling properly "null" as string).
But, with this solution you have to be very careful with changing model names. And remeber to do not obfuscate your models.
Also, quite better soltuion is adding Annotation which keeps policy name as annotation property (then problem with changing field name in app will disappear).