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Look up the class discriminator value by its name in the PolymorphismDecoder #28

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Look up the class discriminator value by its name in the PolymorphismDecoder #28

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95 changes: 53 additions & 42 deletions src/main/kotlin/com/github/jershell/kbson/BsonFlexibleDecoder.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,9 @@ package com.github.jershell.kbson
import kotlinx.serialization.DeserializationStrategy
import kotlinx.serialization.InternalSerializationApi
import kotlinx.serialization.SerializationException
import kotlinx.serialization.descriptors.*
import kotlinx.serialization.descriptors.PolymorphicKind
import kotlinx.serialization.descriptors.SerialDescriptor
import kotlinx.serialization.descriptors.StructureKind
import kotlinx.serialization.encoding.AbstractDecoder
import kotlinx.serialization.encoding.CompositeDecoder
import kotlinx.serialization.encoding.CompositeDecoder.Companion.UNKNOWN_NAME
Expand All @@ -18,26 +20,14 @@ abstract class FlexibleDecoder(
override val serializersModule: SerializersModule,
val configuration: Configuration
) : AbstractDecoder() {

/**
* _id field comes always first in MongoDb.
* Sometimes you may need to check if this id is not already read by the [reader]
* - and then you may need to set the [alreadyReadId] to null in order to specify that is has been taken into account.
*/
open var alreadyReadId: Any?
get() = null
set(_) {
//do nothing
}

override fun beginStructure(descriptor: SerialDescriptor): CompositeDecoder {
return when (descriptor.kind) {
StructureKind.CLASS -> {
val current = reader.currentBsonType
if (current == null || current == BsonType.DOCUMENT) {
reader.readStartDocument()
}
BsonFlexibleDecoder(reader, serializersModule, configuration, alreadyReadId)
BsonFlexibleDecoder(reader, serializersModule, configuration)
}
StructureKind.MAP -> {
reader.readStartDocument()
Expand All @@ -49,7 +39,7 @@ abstract class FlexibleDecoder(
}
is PolymorphicKind -> {
reader.readStartDocument()
PolymorphismDecoder(reader, serializersModule, configuration, alreadyReadId)
PolymorphismDecoder(reader, serializersModule, configuration)
}
else -> this
}
Expand Down Expand Up @@ -136,7 +126,6 @@ class BsonFlexibleDecoder(
reader: AbstractBsonReader,
context: SerializersModule,
configuration: Configuration,
override var alreadyReadId: Any? = null
) : FlexibleDecoder(reader, context, configuration) {

//to handle not optional nullable properties
Expand Down Expand Up @@ -191,14 +180,6 @@ class BsonFlexibleDecoder(

override fun decodeElementIndex(descriptor: SerialDescriptor): Int {
initNotOptionalProperties(descriptor)
if (alreadyReadId != null) {
val idIndex = descriptor.getElementIndex("_id")
if (idIndex != UNKNOWN_NAME) {
return idIndex
} else {
alreadyReadId = null
}
}

if (reader.state == State.TYPE) {
reader.readBsonType()
Expand Down Expand Up @@ -233,43 +214,54 @@ class BsonFlexibleDecoder(
}
return null
}

override fun decodeString(): String =
if (alreadyReadId != null) {
val result = alreadyReadId
alreadyReadId = null
result as? String ?: (result as ObjectId).toString()
} else {
super.decodeString()
}
}

private class PolymorphismDecoder(
reader: AbstractBsonReader,
val context: SerializersModule,
configuration: Configuration,
override var alreadyReadId: Any? = null
) : FlexibleDecoder(reader, context, configuration) {
private var decodeCount = 0
private var discriminatorValue: String? = null

@InternalSerializationApi
override fun <T> decodeSerializableValue(deserializer: DeserializationStrategy<T>): T =
deserializer.deserialize(BsonFlexibleDecoder(reader, context, configuration, alreadyReadId))
deserializer.deserialize(BsonFlexibleDecoder(reader, context, configuration))

override fun decodeElementIndex(descriptor: SerialDescriptor): Int {
val classDiscriminator = descriptor.classDiscriminator()
return when (decodeCount) {
0 -> {
if (reader.state == State.TYPE) {
reader.readBsonType()
}
val fieldName = reader.readName()
if (fieldName == "_id") {
alreadyReadId = when (reader.currentBsonType) {
BsonType.OBJECT_ID -> reader.readObjectId()
BsonType.STRING -> reader.readString()
else -> error("only ObjectId or string are supported as _id for polymorphism decoder ")

val mark = reader.mark

while (discriminatorValue == null) {
when(reader.state) {
State.TYPE -> {
reader.readBsonType()
}
State.NAME -> {
val fieldName = reader.readName()
if (fieldName == classDiscriminator) {
discriminatorValue = reader.readString()
break
} else {
reader.skipValue()
}
}
else -> {
return CompositeDecoder.DECODE_DONE
}
}
}
if (discriminatorValue == null) {
error("Class discriminator field '$classDiscriminator' not found")
}

mark.reset()
decodeCount++
}
1 -> {
Expand All @@ -278,6 +270,25 @@ private class PolymorphismDecoder(
else -> CompositeDecoder.DECODE_DONE
}
}

override fun decodeString(): String {
val currentDiscriminatorValue = discriminatorValue
return if (currentDiscriminatorValue != null) {
discriminatorValue = null
currentDiscriminatorValue
} else {
super.decodeString()
}
}

private fun SerialDescriptor.classDiscriminator(): String {
for (annotation in this.annotations) {
if (annotation is BsonClassDiscriminator) {
return annotation.discriminator
}
}
return configuration.classDiscriminator
}
}

private class MapDecoder(
Expand Down Expand Up @@ -391,4 +402,4 @@ private class ListDecoder(
val nextType = reader.readBsonType()
return if (nextType == BsonType.END_OF_DOCUMENT) CompositeDecoder.DECODE_DONE else index++
}
}
}
22 changes: 22 additions & 0 deletions src/test/kotlin/com/github/jershell/kbson/KBsonTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -1306,6 +1306,18 @@ class KBsonTest {
})
}

// class discriminator at a non-standard location
val doc6 = BsonDocument().apply {
append("payload", BsonDocument().apply {
append("_id", BsonObjectId(ObjectId("5d1777814e8c7b408a6ada73")))
append("someData", BsonString("something"))
append(
conf.classDiscriminator,
BsonString("com.github.jershell.kbson.models.polymorph.SMessage.DataWithObjectId")
)
})
}

val polyBson = KBson(serializersModule = DefaultModule + pModule)

val res1 = polyBson.parse(SealedWrapper.serializer(), doc1)
Expand All @@ -1318,6 +1330,8 @@ class KBsonTest {

val res5 = polyBson.parse(SealedWrapper.serializer(), doc5)

val res6 = polyBson.parse(SealedWrapper.serializer(), doc6)

assertTrue(res1.payload is SMessage.Error)
assertTrue(res2.payload is SMessage.Loading)
assertEquals(SealedWrapper(SMessage.Data(someData = "something")), res3)
Expand All @@ -1330,6 +1344,14 @@ class KBsonTest {
)
), res5
)
assertEquals(
SealedWrapper(
SMessage.DataWithObjectId(
someData = "something",
_id = ObjectId("5d1777814e8c7b408a6ada73")
)
), res6
)
}

@Test
Expand Down