How to change the parsing?

Question

I have the following json :

{
"id":"123",
"nbElements":15,
"containers":[
  {
    "id":"cont1",
    "capacity":3
  }
],
"operations":[
  {
    "id":"cont1_01",
    "weight":3,
    "containerId":"cont1"
  },
  {
    "id":"cont1_02",
    "weight": 4, 
    "containerId":"cont1"
  }
]
}

I created the following classes:

data class Instance (
    val id: String,
    val nbElements: Long,
    val containers: List<Container>,
    val operations: List<Operation>
)

data class Container (
    val id: String,
    val capacity: Long
)

data class Operation (
    val id: String,
    val weight: Long,
    val containerId: String
)

And I am parsing it using Moshi

val adapter = Moshi.Builder().addLast(KotlinJsonAdapterFactory()).build().adapter<Instance>(Instance::class.java)`
val instance: Instance? = adapter.fromJson(request)

N.B request here is just the json object sent by an API or a Message-oriented middleware

However, I am not happy with that for several reasons.

First, I want to use a HashMap for containers and operations where the keys are the identifiers. Thus I will be able to access an operation object easily using its key.

Second, I want to store the container as a full object in each operation. Thus I can do thins like operation.container.capacity

Any ideas on improving my code?

Answer 1

My recommendation would be to use different models for different layers of the application. For example:

Remote Model:

data class InstanceRemoteModel (
    val id: String,
    val nbElements: Long,
    val containers: List<Container>,
    val operations: List<Operation>
)

data class ContainerRemoteModel (
    val id: String,
    val capacity: Long
)

data class OperationRemoteModel (
    val id: String,
    val weight: Long,
    val containerId: String
)

DomainModel:

data class Instance (
    val id: String,
    val elementCount: Long,
    val containers: Map<String, Container>,
    val operations: Map<String, Operation>
)

data class Container (
    val id: String,
    val capacity: Long
)

data class Operation (
    val id: String,
    val weight: Long,
    val container: Container
)

You can a have repository layer wherein you can convert remote models to domain models. Something like so:

class InstanceRepository(...) {
    suspend fun getInstance(...) : Instance {
        //Get data from Server
        //Map models using mapper classes/functions

        return instance
    }
}

Now, in your ViewModel you can access data from the repository.

Note that the above example is just for sake of demonstration. You can tailor your code as you like. The example demonstrates that you are not restricted to the form of data you receive from a remote source and that you can design your model as you require for your application. Data from a remote source is designed so as to efficiently transfer data and is not necessarily how the client application requires it.

Here are useful resources for better understanding:

1. DTO
2. Repository pattern
3. Functional data mappers