Fix PUT merge handling for polymorphic properties.

We now replace the original value of polymorphic properties with the newly deserialized one if the type of the new one is different from the old one. We still copy all JSON ignored properties to the new instance to make sure that non-exposed, server-side state is retained. We apply the same handling for explicitly immutable source and/or target types.

Fixes #2130.

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/DomainObjectReaderUnitTests.java

@@ -55,6 +55,9 @@ import com.fasterxml.jackson.annotation.JsonAutoDetect;
 import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
 import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.DeserializationContext;
@@ -104,6 +107,8 @@ class DomainObjectReaderUnitTests {
 		mappingContext.getPersistentEntity(Note.class);
 		mappingContext.getPersistentEntity(WithNullCollection.class);
 		mappingContext.getPersistentEntity(ArrayHolder.class);
+		mappingContext.getPersistentEntity(Apple.class);
+		mappingContext.getPersistentEntity(Pear.class);
 		mappingContext.afterPropertiesSet();
 
 		this.entities = new PersistentEntities(Collections.singleton(mappingContext));
@@ -587,6 +592,32 @@ class DomainObjectReaderUnitTests {
 		assertThat(updated.array).containsExactly("new");
 	}
 
+	@Test // #2130
+	void writesPolymorphicArrayWithSwitchedItemForPut() throws Exception {
+
+		Apple apple = new Apple();
+		apple.apple = "apple";
+		apple.color = "red";
+		apple.ignored = "ignored";
+
+		Pear pear = new Pear();
+		pear.pear = "pear";
+
+		Fruit result = reader.mergeForPut(pear, apple, new ObjectMapper());
+
+		assertThat(result).isInstanceOfSatisfying(Pear.class, it -> {
+
+			// Exposed property is wiped as expected for PUT
+			assertThat(it.color).isNull();
+
+			// Non-exposed state is transferred
+			assertThat(it.ignored).isEqualTo("ignored");
+
+			// Type specific state applied, too
+			assertThat(it.pear).isEqualTo("pear");
+		});
+	}
+
 	@SuppressWarnings("unchecked")
 	private static <T> T as(Object source, Class<T> type) {
 
@@ -812,4 +843,32 @@ class DomainObjectReaderUnitTests {
 	static class ArrayHolder {
 		String[] array;
 	}
+
+	// DATAREST-1026
+
+	@JsonAutoDetect(fieldVisibility = Visibility.ANY)
+	static class Basket {
+
+		@Id Long id;
+		List<Fruit> fruits;
+	}
+
+	@JsonAutoDetect(fieldVisibility = Visibility.ANY)
+	@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = As.PROPERTY, property = "type")
+	@JsonSubTypes({ @JsonSubTypes.Type(name = "Apple", value = Apple.class),
+			@JsonSubTypes.Type(name = "Pear", value = Pear.class) })
+	static class Fruit {
+		String color;
+		@JsonIgnore String ignored;
+	}
+
+	@JsonAutoDetect(fieldVisibility = Visibility.ANY)
+	static class Apple extends Fruit {
+		String apple;
+	}
+
+	@JsonAutoDetect(fieldVisibility = Visibility.ANY)
+	static class Pear extends Fruit {
+		String pear;
+	}
 }

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/MappedPropertiesUnitTests.java

@@ -115,6 +115,11 @@ class MappedPropertiesUnitTests {
 		assertThat(properties.isWritableProperty("someRandomProperty")).isTrue();
 	}
 
+	@Test // #2130
+	void exposesIgnoredProperties() {
+		assertThat(properties.getIgnoredProperties()).contains("notExposedByJackson");
+	}
+
 	static class Sample {
 
 		public @Transient String notExposedBySpringData;