Gradle GraphQL Scalar Mapping

To generate client DSL from our GraphQL schema, we have to provide mapping of scalars, defined in the schema, to Kotlin data types.

Default mapping

Kobby provides default mapping for some scalars:

GraphQL Scalar	Kotlin Type
ID	kotlin.Long
Int	kotlin.Int
Long	kotlin.Long
Float	kotlin.Double
Double	kotlin.Double
String	kotlin.String
Boolean	kotlin.Boolean

Custom mapping

You can configure your own mapping or override default mapping by means of kobby.kotlin.scalars property:

kobby {
    kotlin {
        scalars = mapOf(
            "ID" to typeOf("java.util", "UUID"),
            "Date" to typeOf("java.time", "LocalDate")
        )
    }
}

The scalars property is of type Map<String, KotlinType>, where key of the map is name of GraphQL scalar and value of the map is Kobby KotlinType:

package io.github.ermadmi78.kobby.generator.kotlin

class KotlinType(
    /** A fully-qualified package name. For example: kotlin.collections */
    val packageName: String,

    /** A fully-qualified class name. For example: Map.Entry */
    val className: String,

    val allowNull: Boolean = false,

    /** List of generics */
    val generics: List<KotlinType> = listOf()
) {
    fun nullable(): KotlinType =
        if (allowNull) this else KotlinType(packageName, className, true, generics)

    fun parameterize(vararg arguments: KotlinType): KotlinType =
        if (arguments.isEmpty()) this else KotlinType(packageName, className, allowNull, generics + arguments)

    fun nested(nestedClassName: String): KotlinType =
        KotlinType(packageName, "$className.$nestedClassName", allowNull, generics)
}

To simplify KotlinType creation, Kobby extension provides builder functions:

package io.github.ermadmi78.kobby

fun typeOf(packageName: String, className: String, vararg arguments: KotlinType) =
    KotlinType(packageName, className, false, arguments.toList())

fun typeOf(packageName: String, className: String, nullable: Boolean, vararg arguments: KotlinType) =
    KotlinType(packageName, className, nullable, arguments.toList())

For example, let configure Map<String, Any?> type for JSON scalar:

import io.github.ermadmi78.kobby.kobby

kobby {
    kotlin {
        scalars = mapOf(
            "JSON" to typeOf(
                "kotlin.collections", "Map",
                typeOf("kotlin", "String"),
                typeOf("kotlin", "Any", nullable = true)
            )
        )
    }
}

Let simplify our example by means of parameterize and nullable functions:

import io.github.ermadmi78.kobby.kobby

kobby {
    kotlin {
        scalars = mapOf(
            "JSON" to typeOf("kotlin.collections", "Map").parameterize(
                typeOf("kotlin", "String"),
                typeOf("kotlin", "Any").nullable()
            )
        )
    }
}

Kotlin standard type constants

The Kobby extension provides a set of predefined constants for standard Kotlin types. With the help of constants, we can rewrite our example like this:

import io.github.ermadmi78.kobby.kobby

kobby {
    kotlin {
        scalars = mapOf(
            "JSON" to typeMap.parameterize(typeString, typeAny.nullable())
        )
    }
}

All available constants:

Constant	Kotlin Type
typeAny	kotlin.Any
typeNumber	kotlin.Number
typeByte	kotlin.Byte
typeShort	kotlin.Short
typeInt	kotlin.Int
typeLong	kotlin.Long
typeFloat	kotlin.Float
typeDouble	kotlin.Double
typeChar	kotlin.Char
typeString	kotlin.String
typeCharSequence	kotlin.CharSequence
typeBoolean	kotlin.Boolean
typeEnum	kotlin.Enum
typeThrowable	kotlin.Throwable
typeComparable	kotlin.Comparable
typeIterable	kotlin.collections.Iterable
typeCollection	kotlin.collections.Collection
typeList	kotlin.collections.List
typeSet	kotlin.collections.Set
typeMap	kotlin.collections.Map
typeMutableIterable	kotlin.collections.MutableIterable
typeMutableCollection	kotlin.collections.MutableCollection
typeMutableList	kotlin.collections.MutableList
typeMutableSet	kotlin.collections.MutableSet
typeMutableMap	kotlin.collections.MutableMap
typeArray	kotlin.Array
typeBooleanArray	kotlin.BooleanArray
typeByteArray	kotlin.ByteArray
typeCharArray	kotlin.CharArray
typeShortArray	kotlin.ShortArray
typeIntArray	kotlin.IntArray
typeLongArray	kotlin.LongArray
typeFloatArray	kotlin.FloatArray
typeDoubleArray	kotlin.DoubleArray

Custom Kotlinx Serializers

You can configure a custom serializer to any type associated with a scalar (see Kotlinx Serialization support):

kobby {
    kotlin {
        scalars = mapOf(
            "Date" to typeOf("java.time", "LocalDate")
                .serializer(
                    "io.github.ermadmi78.kobby.cinema.api.kobby.kotlin.dto", // package name
                    "LocalDateSerializer" // class name
                )
        )
    }
}