The Kotlin counterpart to the TypeScript Omit utility type

Question

The Kotlin counterpart to the TypeScript Omit utility type

Two data classes in Kotlin are very similar, with the only difference being that one contains an ID field while the other does not (the ID is generated only if the model is stored in the database).

data class RouteWithId(
    val id: String,
    val name: String,
    val description: String,
    val comments: List<Comment>,
    val media: List<Media>,
    val points: List<RoutePoint>,
    val userId: String,
    val status: RouteState,
    val tracks: List<TrackInfo>,
) {
    enum class RouteState(val value: String){
        IN_REVIEW("in-review"),
        PUBLISHED("published");
    }
}

data class Route(
    val name: String,
    val description: String,
    val comments: List<Comment>,
    val media: List<Media>,
    val points: List<RoutePoint>,
    val userId: String,
    val status: RouteState,
    val tracks: List<TrackInfo>,
) {
    enum class RouteState(val value: String){
        IN_REVIEW("in-review"),
        PUBLISHED("published");
    }
}

An attempt was made to combine them with a nullable ID field, which resulted in unnecessary complexity since the ID is expected to exist in many instances (such as post-processing after database retrieval).

In TypeScript, there is a utility type called Omit that can derive a type from another type by excluding certain fields.

This approach would be ideal for this scenario, as it is known that the field will exist after database retrieval and will not exist before that.

Is there a way to achieve the same functionality in Kotlin?

typescript kotlin data-class

Answer 1

Answer №1

Summary: Achieving the desired outcome "properly" in an Object-Oriented Language like Kotlin may pose challenges.

Solution:

To delve into the core of Object-Oriented Languages, let's explore the concept of Inheritance. (Click here for a detailed explanation)

Inheritance allows objects to establish relationships and subclasses, facilitating reuse of common logic while retaining a distinct hierarchy. By adhering to this principle, developers conduct comprehensive data analysis, streamline development processes, and enhance precision.

According to the essence of Inheritance, a subclass is obligated to inherit all properties of its parent class without discretion. It cannot selectively choose which properties to inherit.

For instance, if the parent class features a property such as Lung Cancer, then the child class must also incorporate the same Lung Cancer property. The child class cannot simply decline inheriting certain properties based on personal preferences.

Furthermore, let's examine the definition of Data class in Kotlin. (Explore the Data Class definition here) Kotlin imposes strict guidelines on Data class, specifying that it cannot have both a parent and child class relationship. Therefore, using Inheritance with Data Class is not feasible. Instead, traditional classes should be employed.

If absolutely necessary, one can resort to creatively utilizing abstract and interface classes in Kotlin to work around this limitation. However, this practice contradicts fundamental OOP principles and warrants reconsideration of modeling systems. (Have you pondered leveraging Optional in Kotlin instead?)

Here's a sample illustration:

//Define an interface enforcing an ID
interface HasID {
    val id: Int
}

//Data Class ensuring presence of ID
data class RouteWithId(val length: Int, override val id: Int) : HasID

//Data Class lacking an ID
data class RouteWithoutId(val name: String)

If you require further clarification, feel free to inquire. Appreciate your attention.

Answer 2

Summary: Achieving the desired outcome "properly" in an Object-Oriented Language like Kotlin may pose challenges.

Solution:

To delve into the core of Object-Oriented Languages, let's explore the concept of Inheritance. (Click here for a detailed explanation)

Inheritance allows objects to establish relationships and subclasses, facilitating reuse of common logic while retaining a distinct hierarchy. By adhering to this principle, developers conduct comprehensive data analysis, streamline development processes, and enhance precision.

According to the essence of Inheritance, a subclass is obligated to inherit all properties of its parent class without discretion. It cannot selectively choose which properties to inherit.

For instance, if the parent class features a property such as Lung Cancer, then the child class must also incorporate the same Lung Cancer property. The child class cannot simply decline inheriting certain properties based on personal preferences.

Furthermore, let's examine the definition of Data class in Kotlin. (Explore the Data Class definition here) Kotlin imposes strict guidelines on Data class, specifying that it cannot have both a parent and child class relationship. Therefore, using Inheritance with Data Class is not feasible. Instead, traditional classes should be employed.

If absolutely necessary, one can resort to creatively utilizing abstract and interface classes in Kotlin to work around this limitation. However, this practice contradicts fundamental OOP principles and warrants reconsideration of modeling systems. (Have you pondered leveraging Optional in Kotlin instead?)

Here's a sample illustration:

//Define an interface enforcing an ID
interface HasID {
    val id: Int
}

//Data Class ensuring presence of ID
data class RouteWithId(val length: Int, override val id: Int) : HasID

//Data Class lacking an ID
data class RouteWithoutId(val name: String)

If you require further clarification, feel free to inquire. Appreciate your attention.

Answer 3

Answer №2

In Kotlin, there isn't direct support for union types, but you can utilize inheritance to simulate this functionality:

class Route(val name: String, val description: String, /* ... */) {
    enum class RouteState(val value: String){
        IN_REVIEW("in-review"),
        PUBLISHED("published");
    }
    
    fun withId(id: Int): DBRoute = DBRoute(id, name, description, /* ... */)
}

class DBRoute(val id: Int, name: String, description: String, /* ... */) : Route(name, description) {    
    fun asRoute(): Route = Route(name, description, /* ... */)
}

This approach allows you to easily convert a Route instance to a DBRoute and vice versa. One downside is that you need to list all fields from Route in the constructor of DBRoute.

If creating a new class seems excessive, you may consider using a Map<Int, Route> instead. However, if you require specific operations involving the ID, a dedicated class would be more suitable.

Answer 4

In Kotlin, there isn't direct support for union types, but you can utilize inheritance to simulate this functionality:

class Route(val name: String, val description: String, /* ... */) {
    enum class RouteState(val value: String){
        IN_REVIEW("in-review"),
        PUBLISHED("published");
    }
    
    fun withId(id: Int): DBRoute = DBRoute(id, name, description, /* ... */)
}

class DBRoute(val id: Int, name: String, description: String, /* ... */) : Route(name, description) {    
    fun asRoute(): Route = Route(name, description, /* ... */)
}

This approach allows you to easily convert a Route instance to a DBRoute and vice versa. One downside is that you need to list all fields from Route in the constructor of DBRoute.

If creating a new class seems excessive, you may consider using a Map<Int, Route> instead. However, if you require specific operations involving the ID, a dedicated class would be more suitable.

Answer 5

Answer №3

I have been longing for something like this for quite some time. Unfortunately, I am unable to find a satisfactory solution. One approach that comes to mind is creating a custom annotation library using tools like KAPT or KotlinPoet to automatically generate the required classes. Perhaps an API similar to the following could be implemented:

// generates SimplePerson class with name and age fields
@Pick("SimplePerson", fields=["name", "age"])
// creates AgelessPerson class without the age field
@Omit("AgelessPerson", fields=["age"])
data class Person(val name: String, val age: Int, val heightCm: Int, val weight: Int)

Answer 6

I have been longing for something like this for quite some time. Unfortunately, I am unable to find a satisfactory solution. One approach that comes to mind is creating a custom annotation library using tools like KAPT or KotlinPoet to automatically generate the required classes. Perhaps an API similar to the following could be implemented:

// generates SimplePerson class with name and age fields
@Pick("SimplePerson", fields=["name", "age"])
// creates AgelessPerson class without the age field
@Omit("AgelessPerson", fields=["age"])
data class Person(val name: String, val age: Int, val heightCm: Int, val weight: Int)

The Kotlin counterpart to the TypeScript Omit utility type

Answer №1

Solution:

Answer №2

Answer №3

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