DATAMONGO-1726 - Add oneValue() and firstValue() to FluentMongoOperations returning nullable types.

We leave the choice of using Optional open by also providing terminating find operation methods that return null instead of Optional.

Original pull request: #475.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ExecutableFindOperation.java

@@ -73,14 +73,33 @@ public interface ExecutableFindOperation {
 		 * @return {@link Optional#empty()} if no match found.
 		 * @throws org.springframework.dao.IncorrectResultSizeDataAccessException if more than one match found.
 		 */
-		Optional<T> one();
+		default Optional<T> one() {
+			return Optional.ofNullable(oneValue());
+		}
+
+		/**
+		 * Get exactly zero or one result.
+		 *
+		 * @return {@literal null} if no match found.
+		 * @throws org.springframework.dao.IncorrectResultSizeDataAccessException if more than one match found.
+		 */
+		T oneValue();
 
 		/**
 		 * Get the first or no result.
 		 *
 		 * @return {@link Optional#empty()} if no match found.
 		 */
-		Optional<T> first();
+		default Optional<T> first() {
+			return Optional.ofNullable(firstValue());
+		}
+
+		/**
+		 * Get the first or no result.
+		 *
+		 * @return {@literal null} if no match found.
+		 */
+		T firstValue();
 
 		/**
 		 * Get all matching elements.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ExecutableFindOperationSupport.java

@@ -104,27 +104,27 @@ class ExecutableFindOperationSupport implements ExecutableFindOperation {
 		}
 
 		@Override
-		public Optional<T> one() {
+		public T oneValue() {
 
 			List<T> result = doFind(new DelegatingQueryCursorPreparer(getCursorPreparer(query, null)).limit(2));
 
 			if (ObjectUtils.isEmpty(result)) {
-				return Optional.empty();
+				return null;
 			}
 
 			if (result.size() > 1) {
 				throw new IncorrectResultSizeDataAccessException("Query " + asString() + " returned non unique result.", 1);
 			}
 
-			return Optional.of(result.iterator().next());
+			return result.iterator().next();
 		}
 
 		@Override
-		public Optional<T> first() {
+		public T firstValue() {
 
 			List<T> result = doFind(new DelegatingQueryCursorPreparer(getCursorPreparer(query, null)).limit(1));
 
-			return ObjectUtils.isEmpty(result) ? Optional.empty() : Optional.of(result.iterator().next());
+			return ObjectUtils.isEmpty(result) ? null : result.iterator().next();
 		}
 
 		@Override

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ExecutableFindOperationSupportTests.java

@@ -140,6 +140,30 @@ public class ExecutableFindOperationSupportTests {
 		template.query(Person.class).matching(query(where("firstname").in("han", "luke"))).one();
 	}
 
+	@Test // DATAMONGO-1726
+	public void findByReturningOneValue() {
+		assertThat(template.query(Person.class).matching(query(where("firstname").is("luke"))).oneValue()).isEqualTo(luke);
+	}
+
+	@Test(expected = IncorrectResultSizeDataAccessException.class) // DATAMONGO-1726
+	public void findByReturningOneValueButTooManyResults() {
+		template.query(Person.class).matching(query(where("firstname").in("han", "luke"))).oneValue();
+	}
+
+	@Test // DATAMONGO-1726
+	public void findByReturningFirstValue() {
+
+		assertThat(template.query(Person.class).matching(query(where("firstname").is("luke"))).firstValue())
+				.isEqualTo(luke);
+	}
+
+	@Test // DATAMONGO-1726
+	public void findByReturningFirstValueForManyResults() {
+
+		assertThat(template.query(Person.class).matching(query(where("firstname").in("han", "luke"))).firstValue())
+				.isIn(han, luke);
+	}
+
 	@Test // DATAMONGO-1563
 	public void streamAll() {