Support IsEmpty and IsNotEmpty keywords in derived queries

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/MongoQueryCreator.java

@@ -26,6 +26,7 @@
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.bson.BsonRegularExpression;
+import org.bson.Document;
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.data.core.PropertyPath;
@@ -65,6 +66,7 @@
  * @author Thomas Darimont
  * @author Christoph Strobl
  * @author Edward Prentice
+ * @author Junhyeong Choi
  */
 public class MongoQueryCreator extends AbstractQueryCreator<Query, Criteria> {
 
@@ -218,6 +220,10 @@ private Criteria from(Part part, MongoPersistentProperty property, Criteria crit
 				return criteria.is(true);
 			case FALSE:
 				return criteria.is(false);
+			case IS_EMPTY:
+				return createIsEmptyCriteria(property, criteria);
+			case IS_NOT_EMPTY:
+				return createIsNotEmptyCriteria(property, criteria);
 			case NEAR:
 				return createNearCriteria(property, criteria, parameters);
 			case WITHIN:
@@ -254,6 +260,60 @@ protected Criteria exists(Criteria criteria, Object param) {
 		return criteria.exists((Boolean) param);
 	}
 
+	/**
+	 * Creates a criterion for the {@literal IS_EMPTY} keyword. For {@link Collection} properties, checks if the
+	 * collection size is 0. For {@link String} properties, checks if the value equals an empty string. For {@link Map}
+	 * and other types, checks if the value equals an empty document.
+	 *
+	 * @param property the property to check.
+	 * @param criteria the criteria to extend.
+	 * @return the extended criteria.
+	 * @since 5.1
+	 */
+	protected Criteria createIsEmptyCriteria(MongoPersistentProperty property, Criteria criteria) {
+
+		if (property.isCollectionLike()) {
+			return criteria.size(0);
+		}
+
+		if (property.isMap()) {
+			return criteria.is(new Document());
+		}
+
+		if (property.getType() == String.class) {
+			return criteria.is("");
+		}
+
+		return criteria.is(new Document());
+	}
+
+	/**
+	 * Creates a criterion for the {@literal IS_NOT_EMPTY} keyword. For {@link Collection} properties, checks if the
+	 * collection size is not 0. For {@link String} properties, checks if the value is not an empty string. For
+	 * {@link Map} and other types, checks if the value is not an empty document.
+	 *
+	 * @param property the property to check.
+	 * @param criteria the criteria to extend.
+	 * @return the extended criteria.
+	 * @since 5.1
+	 */
+	protected Criteria createIsNotEmptyCriteria(MongoPersistentProperty property, Criteria criteria) {
+
+		if (property.isCollectionLike()) {
+			return criteria.not().size(0);
+		}
+
+		if (property.isMap()) {
+			return criteria.ne(new Document());
+		}
+
+		if (property.getType() == String.class) {
+			return criteria.ne("");
+		}
+
+		return criteria.ne(new Document());
+	}
+
 	private Criteria createNearCriteria(MongoPersistentProperty property, Criteria criteria,
 			Iterator<Object> parameters) {
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/AbstractPersonRepositoryIntegrationTests.java

@@ -26,8 +26,10 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Date;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
 import java.util.regex.Pattern;
@@ -93,6 +95,7 @@
  * @author Mark Paluch
  * @author Fırat KÜÇÜK
  * @author Edward Prentice
+ * @author Junhyeong Choi
  */
 @ExtendWith({ SpringExtension.class, DirtiesStateExtension.class })
 @TestInstance(TestInstance.Lifecycle.PER_CLASS)
@@ -1830,4 +1833,117 @@ void allowsToUseComplexTypesInUpdate() {
 		assertThat(repository.findById(dave.getId()).map(Person::getShippingAddresses))
 				.contains(Collections.singleton(address));
 	}
+
+	@Test // GH-4606
+	@DirtiesState
+	void findsByFirstnameIsEmpty() {
+
+		Person emptyFirstname = new Person("", "EmptyFirstname");
+		repository.save(emptyFirstname);
+
+		List<Person> result = repository.findByFirstnameIsEmpty();
+
+		assertThat(result).hasSize(1).contains(emptyFirstname);
+	}
+
+	@Test // GH-4606
+	void findsByFirstnameIsNotEmpty() {
+
+		List<Person> result = repository.findByFirstnameIsNotEmpty();
+
+		assertThat(result).hasSize(all.size()).containsAll(all);
+	}
+
+	@Test // GH-4606
+	@DirtiesState
+	void blankStringIsNotConsideredEmpty() {
+
+		Person blankFirstname = new Person("   ", "BlankFirstname");
+		repository.save(blankFirstname);
+
+		List<Person> emptyResult = repository.findByFirstnameIsEmpty();
+		List<Person> notEmptyResult = repository.findByFirstnameIsNotEmpty();
+
+		assertThat(emptyResult).doesNotContain(blankFirstname);
+		assertThat(notEmptyResult).contains(blankFirstname);
+	}
+
+	@Test // GH-4606
+	@DirtiesState
+	void findsBySkillsIsEmpty() {
+
+		Person emptySkills = new Person("Empty", "Skills");
+		emptySkills.setSkills(Collections.emptyList());
+		repository.save(emptySkills);
+
+		List<Person> result = repository.findBySkillsIsEmpty();
+
+		assertThat(result).contains(emptySkills).doesNotContain(carter, boyd);
+	}
+
+	@Test // GH-4606
+	void findsBySkillsIsNotEmpty() {
+
+		List<Person> result = repository.findBySkillsIsNotEmpty();
+
+		assertThat(result).contains(carter, boyd);
+	}
+
+	@Test // GH-4606
+	@DirtiesState
+	void findsByAddressIsEmpty() {
+
+		Person emptyAddress = new Person("Empty", "Address");
+		emptyAddress.setAddress(new Address());
+		repository.save(emptyAddress);
+
+		dave.setAddress(new Address("street", "zip", "city"));
+		repository.save(dave);
+
+		List<Person> result = repository.findByAddressIsEmpty();
+
+		assertThat(result).contains(emptyAddress).doesNotContain(dave);
+	}
+
+	@Test // GH-4606
+	@DirtiesState
+	void findsByAddressIsNotEmpty() {
+
+		dave.setAddress(new Address("street", "zip", "city"));
+		repository.save(dave);
+
+		List<Person> result = repository.findByAddressIsNotEmpty();
+
+		assertThat(result).contains(dave);
+	}
+
+	@Test // GH-4606
+	@DirtiesState
+	void findsByMetadataIsEmpty() {
+
+		dave.setMetadata(new HashMap<>());
+		repository.save(dave);
+
+		oliver.setMetadata(Map.of("key", "value"));
+		repository.save(oliver);
+
+		List<Person> result = repository.findByMetadataIsEmpty();
+
+		assertThat(result).contains(dave).doesNotContain(oliver);
+	}
+
+	@Test // GH-4606
+	@DirtiesState
+	void findsByMetadataIsNotEmpty() {
+
+		dave.setMetadata(new HashMap<>());
+		repository.save(dave);
+
+		oliver.setMetadata(Map.of("key", "value"));
+		repository.save(oliver);
+
+		List<Person> result = repository.findByMetadataIsNotEmpty();
+
+		assertThat(result).contains(oliver).doesNotContain(dave);
+	}
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/Person.java

@@ -18,6 +18,7 @@
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
 
@@ -39,6 +40,7 @@
  * @author Thomas Darimont
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Junhyeong Choi
  */
 @Document
 public class Person extends Contact {
@@ -81,6 +83,8 @@ public enum Sex {
 
 	int visits;
 
+	Map<String, String> metadata;
+
 	public Person() {
 
 		this(null, null);
@@ -334,6 +338,14 @@ public void setLazySpiritAnimal(User lazySpiritAnimal) {
 		this.lazySpiritAnimal = lazySpiritAnimal;
 	}
 
+	public Map<String, String> getMetadata() {
+		return metadata;
+	}
+
+	public void setMetadata(Map<String, String> metadata) {
+		this.metadata = metadata;
+	}
+
 	@Override
 	public int hashCode() {
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/PersonRepository.java

@@ -56,6 +56,7 @@
  * @author Christoph Strobl
  * @author Fırat KÜÇÜK
  * @author Mark Paluch
+ * @author Junhyeong Choi
  */
 public interface PersonRepository extends MongoRepository<Person, String>, QuerydslPredicateExecutor<Person> {
 
@@ -510,6 +511,30 @@ Person findPersonByManyArguments(String firstname, String lastname, String email
 
 	List<Person> findBySpiritAnimal(User user);
 
+	// GH-4606
+	List<Person> findByFirstnameIsEmpty();
+
+	// GH-4606
+	List<Person> findByFirstnameIsNotEmpty();
+
+	// GH-4606
+	List<Person> findBySkillsIsEmpty();
+
+	// GH-4606
+	List<Person> findBySkillsIsNotEmpty();
+
+	// GH-4606
+	List<Person> findByAddressIsEmpty();
+
+	// GH-4606
+	List<Person> findByAddressIsNotEmpty();
+
+	// GH-4606
+	List<Person> findByMetadataIsEmpty();
+
+	// GH-4606
+	List<Person> findByMetadataIsNotEmpty();
+
 	class Persons implements Streamable<Person> {
 
 		private final Streamable<Person> streamable;