Feature: adjust Option[A] codecs. (#138)

* Introduce decodeOptional, to pass into decoder optional attribute values. * Fix build
PlayQ · Aug 7, 2020 · 4e3058c · 4e3058c
1 parent b22296c
commit 4e3058c
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Showing 3 changed files with 25 additions and 11 deletions.
diff --git a/d4s-circe/src/test/scala/d4s/codecs/DynamoCodecTest.scala b/d4s-circe/src/test/scala/d4s/codecs/DynamoCodecTest.scala
@@ -3,8 +3,8 @@ package d4s.codecs
 import d4s.codecs.Fixtures._
 import d4s.codecs.circe.{D4SCirceAttributeCodec, D4SCirceCodec}
 import d4s.models.DynamoException.DecoderException
-import io.circe.{Decoder, Encoder}
 import io.circe.generic.extras.semiauto
+import io.circe.{Decoder, Encoder}
 import org.scalacheck.Prop
 import org.scalatest.wordspec.AnyWordSpec
 import org.scalatestplus.scalacheck.Checkers
@@ -13,6 +13,11 @@ import software.amazon.awssdk.core.SdkBytes
 import scala.jdk.CollectionConverters._
 
 final class DynamoCodecTest extends AnyWordSpec with Checkers {
+  "decode options from missed attribute" in {
+    val decoder = D4SDecoder.optionDecoder[Int]
+    assert(decoder.decodeOptional(None, "").exists(_.isEmpty))
+  }
+
   "encode/decode TestCaseClass" in check {
     Prop.forAllNoShrink {
       testData: TestCaseClass =>

diff --git a/d4s/src/main/scala/d4s/codecs/D4SDecoder.scala b/d4s/src/main/scala/d4s/codecs/D4SDecoder.scala
@@ -23,6 +23,12 @@ import scala.util.control.NonFatal
 trait D4SDecoder[T] {
   def decode(attr: AttributeValue): Either[DecoderException, T]
   def decodeObject(item: Map[String, AttributeValue]): Either[DecoderException, T]
+  def decodeOptional(attr: Option[AttributeValue], label: String): Either[DecoderException, T] = {
+    attr match {
+      case Some(value) => decode(value)
+      case None        => Left(DecoderException(s"Cannot find parameter with name `$label` of type [${this.getClass.getSimpleName}].", None))
+    }
+  }
 
   final def decodeObject(item: java.util.Map[String, AttributeValue]): Either[DecoderException, T] = decodeObject(item.asScala.toMap)
 
@@ -80,10 +86,8 @@ object D4SDecoder extends D4SDecoderScala213 {
     item =>
       ctx.constructMonadic {
         p =>
-          item.get(p.label) match {
-            case Some(value) => p.typeclass.decode(value)
-            case None        => Left(DecoderException(s"Cannot find parameter with name ${p.label}", None))
-          }
+          val label = p.label
+          p.typeclass.decodeOptional(item.get(label), label)
       }
   }
 
@@ -92,7 +96,7 @@ object D4SDecoder extends D4SDecoderScala213 {
       if (item.m().isEmpty) {
         ctx.subtypes
           .find(_.typeName.short == item.s())
-          .toRight(DecoderException(s" Cannot decode item of type ${ctx.typeName.full} from string: ${item.s()}", None))
+          .toRight(DecoderException(s"Cannot decode item of type [${ctx.typeName.full}] from string: ${item.s()}", None))
           .flatMap(_.typeclass.decode(item))
       } else {
         if (item.m().size != 1) {
@@ -101,7 +105,7 @@ object D4SDecoder extends D4SDecoderScala213 {
           val (typeName, attrValue) = item.m().asScala.head
           ctx.subtypes
             .find(_.typeName.short == typeName)
-            .toRight(DecoderException(s"Cannot find a subtype $typeName for a sealed trait ${ctx.typeName.full}", None))
+            .toRight(DecoderException(s"Cannot find a subtype [$typeName] for a sealed trait [${ctx.typeName.full}]", None))
             .flatMap(_.typeclass.decode(attrValue))
         }
       }
@@ -188,9 +192,14 @@ object D4SDecoder extends D4SDecoderScala213 {
         }
     }
 
-  implicit def optionDecoder[A](implicit T: D4SDecoder[A]): D4SDecoder[Option[A]] = attributeDecoder {
-    attr =>
-      if (attr.nul()) Right(None) else T.decode(attr).map(Some(_))
+  implicit def optionDecoder[A](implicit T: D4SDecoder[A]): D4SDecoder[Option[A]] = new D4SDecoder[Option[A]] {
+    override def decode(attr: AttributeValue): Either[DecoderException, Option[A]]                    = decodeOptional(Some(attr), "")
+    override def decodeObject(item: Map[String, AttributeValue]): Either[DecoderException, Option[A]] = decode(AttributeValue.builder().m(item.asJava).build())
+    override def decodeOptional(attr: Option[AttributeValue], label: String): Either[DecoderException, Option[A]] = attr match {
+      case None                     => Right(None)
+      case Some(attr) if attr.nul() => Right(None)
+      case Some(attr)               => T.decode(attr).map(Some(_))
+    }
   }
 
   implicit def eitherDecoder[A: D4SDecoder, B: D4SDecoder]: D4SDecoder[Either[A, B]] = D4SDecoder.derived

diff --git a/d4s/src/main/scala/d4s/models/DynamoException.scala b/d4s/src/main/scala/d4s/models/DynamoException.scala
@@ -32,7 +32,7 @@ object DynamoException {
     }
   }
 
-  final case class DecoderException(override val message: String, maybeCause: Option[Throwable]) extends DynamoException(message, maybeCause.orNull) {
+  final case class DecoderException(override val message: String, maybeCause: Option[Throwable]) extends DynamoException(message, maybeCause.getOrElse(new RuntimeException(message))) {
     def union(that: DecoderException): DecoderException = {
       val errorLog = message + "\n" + that.getMessage
       DecoderException(errorLog, maybeCause.orElse(that.maybeCause))