add default serializer for documentid + test

model/src/commonMain/kotlin/dev/stashy/mongoservices/model/DocumentId.kt

@@ -1,5 +1,6 @@
 package dev.stashy.mongoservices.model
 
+import kotlinx.serialization.Serializable
 import kotlin.jvm.JvmInline
 
 /**
@@ -23,4 +24,5 @@ import kotlin.jvm.JvmInline
  * ```
  */
 @JvmInline
+@Serializable(with = DocumentIdSerializer::class)
 value class DocumentId(val value: String)

model/src/commonTest/kotlin/DocumentIdSerializationTest.kt

@@ -0,0 +1,36 @@
+import dev.stashy.mongoservices.model.DocumentId
+import dev.stashy.mongoservices.model.DocumentIdSerializer
+import kotlinx.serialization.Contextual
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.modules.SerializersModule
+import kotlinx.serialization.modules.contextual
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class DocumentIdSerializationTest {
+    private val customJson = Json { serializersModule = SerializersModule { contextual(DocumentIdSerializer) } }
+
+    @Serializable
+    data class TestObj(@SerialName("_id") @Contextual val id: @Contextual DocumentId, val foo: String)
+
+    @Test
+    fun `documentId serialization`() {
+        val documentId = DocumentId("test")
+        val serializedDefault = Json.encodeToString(documentId)
+        val serializedCustom = customJson.encodeToString(documentId)
+
+        assertEquals("\"test\"", serializedDefault)
+        assertEquals("\"test\"", serializedCustom)
+    }
+
+    @Test
+    fun `contextual documentId inside an object`() {
+        val documentId = DocumentId("test")
+        val testObj = TestObj(documentId, "test")
+
+        assertEquals(customJson.encodeToString(testObj), Json.encodeToString(testObj))
+    }
+}