DATAES-920 - Add parameter to @Field annotation to store null values.

Original PR: #516

src/main/java/org/springframework/data/elasticsearch/annotations/Field.java

@@ -154,4 +154,11 @@ public @interface Field {
 	 * @since 4.0
 	 */
 	int maxShingleSize() default -1;
+
+	/**
+	 * if true, the field will be stored in Elasticsearch even if it has a null value
+	 * 
+	 * @since 4.1
+	 */
+	boolean storeNullValue() default false;
 }

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

@@ -497,6 +497,11 @@ public class MappingElasticsearchConverter
 			Object value = accessor.getProperty(property);
 
 			if (value == null) {
+
+				if (property.storeNullValue()) {
+					sink.set(property, null);
+				}
+
 				continue;
 			}
 
@@ -797,7 +802,8 @@ public class MappingElasticsearchConverter
 				});
 			}
 
-			org.springframework.data.elasticsearch.annotations.Field fieldAnnotation = property.findAnnotation(org.springframework.data.elasticsearch.annotations.Field.class);
+			org.springframework.data.elasticsearch.annotations.Field fieldAnnotation = property
+					.findAnnotation(org.springframework.data.elasticsearch.annotations.Field.class);
 
 			if (fieldAnnotation != null) {
 				field.setFieldType(fieldAnnotation.type());
@@ -864,14 +870,17 @@ public class MappingElasticsearchConverter
 			return result;
 		}
 
-		public void set(ElasticsearchPersistentProperty property, Object value) {
+		public void set(ElasticsearchPersistentProperty property, @Nullable Object value) {
 
-			if (property.isIdProperty()) {
-				((Document) target).setId(value.toString());
-			}
+			if (value != null) {
 
-			if (property.isVersionProperty()) {
-				((Document) target).setVersion((Long) value);
+				if (property.isIdProperty()) {
+					((Document) target).setId(value.toString());
+				}
+
+				if (property.isVersionProperty()) {
+					((Document) target).setVersion((Long) value);
+				}
 			}
 
 			target.put(property.getFieldName(), value);

src/main/java/org/springframework/data/elasticsearch/core/mapping/ElasticsearchPersistentProperty.java

@@ -96,6 +96,12 @@ public interface ElasticsearchPersistentProperty extends PersistentProperty<Elas
 	 */
 	boolean isReadable();
 
+	/**
+	 * @return {@literal true} if null values should be stored in Elasticsearch
+	 * @since 4.1
+	 */
+	boolean storeNullValue();
+
 	enum PropertyToFieldNameConverter implements Converter<ElasticsearchPersistentProperty, String> {
 
 		INSTANCE;

src/main/java/org/springframework/data/elasticsearch/core/mapping/SimpleElasticsearchPersistentProperty.java

@@ -64,6 +64,7 @@ public class SimpleElasticsearchPersistentProperty extends
 	private final boolean isSeqNoPrimaryTerm;
 	private final @Nullable String annotatedFieldName;
 	@Nullable private ElasticsearchPersistentPropertyConverter propertyConverter;
+	private boolean storeNullValue;
 
 	public SimpleElasticsearchPersistentProperty(Property property,
 			PersistentEntity<?, ElasticsearchPersistentProperty> owner, SimpleTypeHolder simpleTypeHolder) {
@@ -85,6 +86,8 @@ public class SimpleElasticsearchPersistentProperty extends
 		this.isParent = isAnnotationPresent(Parent.class);
 		this.isSeqNoPrimaryTerm = SeqNoPrimaryTerm.class.isAssignableFrom(getRawType());
 
+		boolean isField = isAnnotationPresent(Field.class);
+
 		if (isVersionProperty() && !getType().equals(Long.class)) {
 			throw new MappingException(String.format("Version property %s must be of type Long!", property.getName()));
 		}
@@ -98,11 +101,13 @@ public class SimpleElasticsearchPersistentProperty extends
 			throw new MappingException(String.format("Parent property %s must be of type String!", property.getName()));
 		}
 
-		if (isAnnotationPresent(Field.class) && isAnnotationPresent(MultiField.class)) {
+		if (isField && isAnnotationPresent(MultiField.class)) {
 			throw new MappingException("@Field annotation must not be used on a @MultiField property.");
 		}
 
 		initDateConverter();
+
+		storeNullValue = isField && getRequiredAnnotation(Field.class).storeNullValue();
 	}
 
 	@Override
@@ -126,6 +131,11 @@ public class SimpleElasticsearchPersistentProperty extends
 		return !isTransient() && !isSeqNoPrimaryTermProperty();
 	}
 
+	@Override
+	public boolean storeNullValue() {
+		return storeNullValue;
+	}
+
 	/**
 	 * Initializes an {@link ElasticsearchPersistentPropertyConverter} if this property is annotated as a Field with type
 	 * {@link FieldType#Date}, has a {@link DateFormat} set and if the type of the property is one of the Java8 temporal

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

@@ -39,6 +39,7 @@ import java.util.Map;
 
 import org.json.JSONException;
 import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.converter.Converter;
@@ -616,7 +617,7 @@ public class MappingElasticsearchConverterUnitTests {
 		assertEquals(expected, json, false);
 	}
 
-	@Test
+	@Test // DATAES-716
 	void shouldReadLocalDate() {
 		Document document = Document.create();
 		document.put("id", "4711");
@@ -813,6 +814,25 @@ public class MappingElasticsearchConverterUnitTests {
 		assertEquals(expected, document.toJson(), false);
 	}
 
+	@Test // DATAES-920
+	@DisplayName("should write null value if configured")
+	void shouldWriteNullValueIfConfigured() throws JSONException {
+
+		EntityWithNullField entity = new EntityWithNullField();
+		entity.setId("42");
+
+		String expected = "{\n" + //
+				"  \"id\": \"42\",\n" + //
+				"  \"saved\": null\n" + //
+				"}\n"; //
+
+		Document document = Document.create();
+
+		mappingElasticsearchConverter.write(entity, document);
+
+		assertEquals(expected, document.toJson(), false);
+	}
+
 	private String pointTemplate(String name, Point point) {
 		return String.format(Locale.ENGLISH, "\"%s\":{\"lat\":%.1f,\"lon\":%.1f}", name, point.getX(), point.getY());
 	}
@@ -1046,4 +1066,11 @@ public class MappingElasticsearchConverterUnitTests {
 		@Id private String id;
 		private Object content;
 	}
+
+	@Data
+	static class EntityWithNullField {
+		@Id private String id;
+		@Field(type = FieldType.Text) private String notSaved;
+		@Field(type = FieldType.Text, storeNullValue = true) private String saved;
+	}
 }