Fix mapping of property values into a collection.

When reading from Elasticsearch into a property of type Collection<T> (List<T> or Set<T>) the MappingElasticsearchConverter now can read both from the returned JSON:

    an array of T objects - will put the objects in a corresponding collection
    a single T object will put the single object into a corrsponding colletcion

This is implemented and tested for both: entities where the properties have setters and immutable classes that only provide an all-args constructor.

Original Pull Request #2282
Closes #2280

src/main/java/org/springframework/data/elasticsearch/core/convert/MappingElasticsearchConverter.java

@@ -201,7 +201,7 @@ public class MappingElasticsearchConverter
 	}
 
 	/**
-	 * Class to do the actual writing. The methods originally were in the MappingElasticsearchConverter class, but are
+	 * Class to do the actual reading. The methods originally were in the MappingElasticsearchConverter class, but are
 	 * refactored to allow for keeping state during the conversion of an object.
 	 */
 	private static class Reader extends Base {
@@ -220,10 +220,17 @@ public class MappingElasticsearchConverter
 		}
 
 		@SuppressWarnings("unchecked")
+		/**
+		 * Reads the given source into the given type.
+		 *
+		 * @param type they type to convert the given source to.
+		 * @param source the source to create an object of the given type from.
+		 * @return the object that was read
+		 */
 		<R> R read(Class<R> type, Document source) {
 
-			TypeInformation<R> typeHint = TypeInformation.of((Class<R>) ClassUtils.getUserClass(type));
-			R r = read(typeHint, source);
+			TypeInformation<R> typeInformation = TypeInformation.of((Class<R>) ClassUtils.getUserClass(type));
+			R r = read(typeInformation, source);
 
 			if (r == null) {
 				throw new ConversionException("could not convert into object of class " + type);
@@ -234,11 +241,11 @@ public class MappingElasticsearchConverter
 
 		@Nullable
 		@SuppressWarnings("unchecked")
-		private <R> R read(TypeInformation<R> type, Map<String, Object> source) {
+		private <R> R read(TypeInformation<R> typeInformation, Map<String, Object> source) {
 
 			Assert.notNull(source, "Source must not be null!");
 
-			TypeInformation<? extends R> typeToUse = typeMapper.readType(source, type);
+			TypeInformation<? extends R> typeToUse = typeMapper.readType(source, typeInformation);
 			Class<? extends R> rawType = typeToUse.getType();
 
 			if (conversions.hasCustomReadTarget(source.getClass(), rawType)) {
@@ -256,8 +263,8 @@ public class MappingElasticsearchConverter
 			if (typeToUse.equals(TypeInformation.OBJECT)) {
 				return (R) source;
 			}
-			// Retrieve persistent entity info
 
+			// Retrieve persistent entity info
 			ElasticsearchPersistentEntity<?> entity = mappingContext.getPersistentEntity(typeToUse);
 
 			if (entity == null) {
@@ -372,7 +379,6 @@ public class MappingElasticsearchConverter
 			}
 
 			return result;
-
 		}
 
 		private ParameterValueProvider<ElasticsearchPersistentProperty> getParameterProvider(
@@ -462,12 +468,44 @@ public class MappingElasticsearchConverter
 			} else if (value.getClass().isArray()) {
 				return (T) readCollectionOrArray(type, Arrays.asList((Object[]) value));
 			} else if (value instanceof Map) {
+
+				TypeInformation<?> collectionComponentType = getCollectionComponentType(type);
+				if (collectionComponentType != null) {
+					Object o = read(collectionComponentType, (Map<String, Object>) value);
+					return getCollectionWithSingleElement(type, collectionComponentType, o);
+				}
 				return (T) read(type, (Map<String, Object>) value);
 			} else {
+
+				TypeInformation<?> collectionComponentType = getCollectionComponentType(type);
+				if (collectionComponentType != null
+						&& collectionComponentType.isAssignableFrom(TypeInformation.of(value.getClass()))) {
+					Object o = getPotentiallyConvertedSimpleRead(value, collectionComponentType);
+					return getCollectionWithSingleElement(type, collectionComponentType, o);
+				}
+
 				return (T) getPotentiallyConvertedSimpleRead(value, rawType);
 			}
 		}
 
+		@SuppressWarnings("unchecked")
+		private static <T> T getCollectionWithSingleElement(TypeInformation<?> collectionType,
+				TypeInformation<?> componentType, Object element) {
+			Collection<Object> collection = CollectionFactory.createCollection(collectionType.getType(),
+					componentType.getType(), 1);
+			collection.add(element);
+			return (T) collection;
+		}
+
+		/**
+		 * @param type the type to check
+		 * @return true if type is a collectoin, null otherwise,
+		 */
+		@Nullable
+		TypeInformation<?> getCollectionComponentType(TypeInformation<?> type) {
+			return type.isCollectionLike() ? type.getComponentType() : null;
+		}
+
 		private Object propertyConverterRead(ElasticsearchPersistentProperty property, Object source) {
 			PropertyValueConverter propertyValueConverter = Objects.requireNonNull(property.getPropertyValueConverter());
 
@@ -1148,17 +1186,18 @@ public class MappingElasticsearchConverter
 
 		Assert.notNull(query, "query must not be null");
 
-		if (domainClass != null) {
+		if (domainClass == null) {
+			return;
+		}
 
-			updateFieldsAndSourceFilter(query, domainClass);
+		updatePropertiesInFieldsAndSourceFilter(query, domainClass);
 
-			if (query instanceof CriteriaQuery) {
-				updateCriteriaQuery((CriteriaQuery) query, domainClass);
-			}
+		if (query instanceof CriteriaQuery) {
+			updatePropertiesInCriteriaQuery((CriteriaQuery) query, domainClass);
 		}
 	}
 
-	private void updateFieldsAndSourceFilter(Query query, Class<?> domainClass) {
+	private void updatePropertiesInFieldsAndSourceFilter(Query query, Class<?> domainClass) {
 
 		ElasticsearchPersistentEntity<?> persistentEntity = mappingContext.getPersistentEntity(domainClass);
 
@@ -1196,14 +1235,22 @@ public class MappingElasticsearchConverter
 		}
 	}
 
-	private List<String> updateFieldNames(List<String> fields, ElasticsearchPersistentEntity<?> persistentEntity) {
-		return fields.stream().map(fieldName -> {
+	/**
+	 * relaces the fieldName with the property name of a property of the persistentEntity with the corresponding
+	 * fieldname. If no such property exists, the original fieldName is kept.
+	 *
+	 * @param fieldNames list of fieldnames
+	 * @param persistentEntity the persistent entity to check
+	 * @return an updated list of field names
+	 */
+	private List<String> updateFieldNames(List<String> fieldNames, ElasticsearchPersistentEntity<?> persistentEntity) {
+		return fieldNames.stream().map(fieldName -> {
 			ElasticsearchPersistentProperty persistentProperty = persistentEntity.getPersistentProperty(fieldName);
 			return persistentProperty != null ? persistentProperty.getFieldName() : fieldName;
 		}).collect(Collectors.toList());
 	}
 
-	private void updateCriteriaQuery(CriteriaQuery criteriaQuery, Class<?> domainClass) {
+	private void updatePropertiesInCriteriaQuery(CriteriaQuery criteriaQuery, Class<?> domainClass) {
 
 		Assert.notNull(criteriaQuery, "criteriaQuery must not be null");
 		Assert.notNull(domainClass, "domainClass must not be null");
@@ -1212,17 +1259,17 @@ public class MappingElasticsearchConverter
 
 		if (persistentEntity != null) {
 			for (Criteria chainedCriteria : criteriaQuery.getCriteria().getCriteriaChain()) {
-				updateCriteria(chainedCriteria, persistentEntity);
+				updatePropertiesInCriteria(chainedCriteria, persistentEntity);
 			}
 			for (Criteria subCriteria : criteriaQuery.getCriteria().getSubCriteria()) {
 				for (Criteria chainedCriteria : subCriteria.getCriteriaChain()) {
-					updateCriteria(chainedCriteria, persistentEntity);
+					updatePropertiesInCriteria(chainedCriteria, persistentEntity);
 				}
 			}
 		}
 	}
 
-	private void updateCriteria(Criteria criteria, ElasticsearchPersistentEntity<?> persistentEntity) {
+	private void updatePropertiesInCriteria(Criteria criteria, ElasticsearchPersistentEntity<?> persistentEntity) {
 
 		Field field = criteria.getField();
 

src/test/java/org/springframework/data/elasticsearch/core/convert/MappingElasticsearchConverterUnitTests.java

@@ -34,7 +34,10 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Collectors;
 
+import org.intellij.lang.annotations.Language;
 import org.json.JSONException;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
@@ -1531,6 +1534,336 @@ public class MappingElasticsearchConverterUnitTests {
 		mappingElasticsearchConverter.updateQuery(query, EntityWithCustomValueConverters.class);
 	}
 
+	@Test // #2280
+	@DisplayName("should read a single String into a List property")
+	void shouldReadASingleStringIntoAListProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringList": "foo"
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getStringList()).containsExactly("foo");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a String array into a List property")
+	void shouldReadAStringArrayIntoAListProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringList": ["foo", "bar"]
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getStringList()).containsExactly("foo", "bar");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a single String into a Set property")
+	void shouldReadASingleStringIntoASetProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringSet": "foo"
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getStringSet()).containsExactly("foo");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a String array into a Set property")
+	void shouldReadAStringArrayIntoASetProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringSet": ["foo", "bar"]
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getStringSet()).containsExactly("foo", "bar");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a single object into a List property")
+	void shouldReadASingleObjectIntoAListProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenList": {
+						"name": "child"
+					}
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenList()).hasSize(1);
+		// noinspection ConstantConditions
+		assertThat(entity.getChildrenList().get(0).getName()).isEqualTo("child");
+	}
+
+	@Test // #2280
+	@DisplayName("should read an object array into a List property")
+	void shouldReadAnObjectArrayIntoAListProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenList": [
+						{
+							"name": "child1"
+						},
+						{
+							"name": "child2"
+						}
+					]
+				}
+								""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenList()).hasSize(2);
+		// noinspection ConstantConditions
+		assertThat(entity.getChildrenList().get(0).getName()).isEqualTo("child1");
+		assertThat(entity.getChildrenList().get(1).getName()).isEqualTo("child2");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a single object into a Set property")
+	void shouldReadASingleObjectIntoASetProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenSet": {
+						"name": "child"
+					}
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenSet()).hasSize(1);
+		// noinspection ConstantConditions
+		assertThat(entity.getChildrenSet().iterator().next().getName()).isEqualTo("child");
+	}
+
+	@Test // #2280
+	@DisplayName("should read an object array into a Set property")
+	void shouldReadAnObjectArrayIntoASetProperty() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenSet": [
+						{
+							"name": "child1"
+						},
+						{
+							"name": "child2"
+						}
+					]
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(EntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenSet()).hasSize(2);
+		// noinspection ConstantConditions
+		List<String> names = entity.getChildrenSet().stream().map(EntityWithCollections.Child::getName)
+				.collect(Collectors.toList());
+		assertThat(names).containsExactlyInAnyOrder("child1", "child2");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a single String into a List property immutable")
+	void shouldReadASingleStringIntoAListPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringList": "foo"
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getStringList()).containsExactly("foo");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a String array into a List property immutable")
+	void shouldReadAStringArrayIntoAListPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringList": ["foo", "bar"]
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getStringList()).containsExactly("foo", "bar");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a single String into a Set property immutable")
+	void shouldReadASingleStringIntoASetPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringSet": "foo"
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getStringSet()).containsExactly("foo");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a String array into a Set property immutable")
+	void shouldReadAStringArrayIntoASetPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"stringSet": ["foo", "bar"]
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getStringSet()).containsExactly("foo", "bar");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a single object into a List property immutable")
+	void shouldReadASingleObjectIntoAListPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenList": {
+						"name": "child"
+					}
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenList()).hasSize(1);
+		// noinspection ConstantConditions
+		assertThat(entity.getChildrenList().get(0).getName()).isEqualTo("child");
+	}
+
+	@Test // #2280
+	@DisplayName("should read an object array into a List property immutable")
+	void shouldReadAnObjectArrayIntoAListPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenList": [
+						{
+							"name": "child1"
+						},
+						{
+							"name": "child2"
+						}
+					]
+				}
+								""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenList()).hasSize(2);
+		// noinspection ConstantConditions
+		assertThat(entity.getChildrenList().get(0).getName()).isEqualTo("child1");
+		assertThat(entity.getChildrenList().get(1).getName()).isEqualTo("child2");
+	}
+
+	@Test // #2280
+	@DisplayName("should read a single object into a Set property immutable")
+	void shouldReadASingleObjectIntoASetPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenSet": {
+						"name": "child"
+					}
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenSet()).hasSize(1);
+		// noinspection ConstantConditions
+		assertThat(entity.getChildrenSet().iterator().next().getName()).isEqualTo("child");
+	}
+
+	@Test // #2280
+	@DisplayName("should read an object array into a Set property immutable")
+	void shouldReadAnObjectArrayIntoASetPropertyImmutable() {
+
+		@Language("JSON")
+		var json = """
+				{
+					"childrenSet": [
+						{
+							"name": "child1"
+						},
+						{
+							"name": "child2"
+						}
+					]
+				}
+				""";
+		Document source = Document.parse(json);
+
+		var entity = mappingElasticsearchConverter.read(ImmutableEntityWithCollections.class, source);
+
+		assertThat(entity.getChildrenSet()).hasSize(2);
+		// noinspection ConstantConditions
+		List<String> names = entity.getChildrenSet().stream().map(ImmutableEntityWithCollections.Child::getName)
+				.collect(Collectors.toList());
+		assertThat(names).containsExactlyInAnyOrder("child1", "child2");
+	}
+
 	private Map<String, Object> writeToMap(Object source) {
 
 		Document sink = Document.create();
@@ -2472,6 +2805,128 @@ public class MappingElasticsearchConverterUnitTests {
 			return reverse(value);
 		}
 	}
+
+	private static class EntityWithCollections {
+		@Field(type = FieldType.Keyword)
+		@Nullable private List<String> stringList;
+
+		@Field(type = FieldType.Keyword)
+		@Nullable private Set<String> stringSet;
+
+		@Field(type = FieldType.Object)
+		@Nullable private List<Child> childrenList;
+
+		@Field(type = FieldType.Object)
+		@Nullable private Set<Child> childrenSet;
+
+		@Nullable
+		public List<String> getStringList() {
+			return stringList;
+		}
+
+		public void setStringList(@Nullable List<String> stringList) {
+			this.stringList = stringList;
+		}
+
+		@Nullable
+		public Set<String> getStringSet() {
+			return stringSet;
+		}
+
+		public void setStringSet(@Nullable Set<String> stringSet) {
+			this.stringSet = stringSet;
+		}
+
+		@Nullable
+		public List<Child> getChildrenList() {
+			return childrenList;
+		}
+
+		public void setChildrenList(@Nullable List<Child> childrenList) {
+			this.childrenList = childrenList;
+		}
+
+		@Nullable
+		public Set<Child> getChildrenSet() {
+			return childrenSet;
+		}
+
+		public void setChildrenSet(@Nullable Set<Child> childrenSet) {
+			this.childrenSet = childrenSet;
+		}
+
+		public static class Child {
+
+			@Field(type = FieldType.Keyword)
+			@Nullable private String name;
+
+			@Nullable
+			public String getName() {
+				return name;
+			}
+
+			public void setName(String name) {
+				this.name = name;
+			}
+		}
+	}
+
+	private static final class ImmutableEntityWithCollections {
+		@Field(type = FieldType.Keyword)
+		@Nullable private List<String> stringList;
+
+		@Field(type = FieldType.Keyword)
+		@Nullable private Set<String> stringSet;
+
+		@Field(type = FieldType.Object)
+		@Nullable private List<Child> childrenList;
+
+		@Field(type = FieldType.Object)
+		@Nullable private Set<Child> childrenSet;
+
+		public ImmutableEntityWithCollections(@Nullable List<String> stringList, @Nullable Set<String> stringSet,
+																					@Nullable List<Child> childrenList, @Nullable Set<Child> childrenSet) {
+			this.stringList = stringList;
+			this.stringSet = stringSet;
+			this.childrenList = childrenList;
+			this.childrenSet = childrenSet;
+		}
+
+		@Nullable
+		public List<String> getStringList() {
+			return stringList;
+		}
+
+		@Nullable
+		public Set<String> getStringSet() {
+			return stringSet;
+		}
+
+		@Nullable
+		public List<Child> getChildrenList() {
+			return childrenList;
+		}
+
+		@Nullable
+		public Set<Child> getChildrenSet() {
+			return childrenSet;
+		}
+
+		public static class Child {
+
+			@Field(type = FieldType.Keyword)
+			@Nullable private String name;
+
+			public Child(@Nullable String name) {
+				this.name = name;
+			}
+
+			@Nullable
+			public String getName() {
+				return name;
+			}
+		}
+	}
 	// endregion
 
 	private static String reverse(Object o) {