DATAJPA-13 - findOne(Specification s) now returns null if there is no result.

I chose not to return the arbitrary first result in case the Specification returns more than one result. First, there's no way to influence the order of the results so that we potentially get different results for the very same call. Beyond that this aligns with the semantics we have for finder methods that are supposed to return a single entity but actually don't.

src/test/java/org/springframework/data/jpa/domain/sample/UserSpecifications.java

@@ -54,6 +54,27 @@ public class UserSpecifications {
     }
 
 
+    /**
+     * A {@link Specification} to do a like-match on a {@link User}'s firstname.
+     * 
+     * @param firstname
+     * @return
+     */
+    public static Specification<User> userHasFirstnameLike(
+            final String expression) {
+
+        return new Specification<User>() {
+
+            public Predicate toPredicate(Root<User> root,
+                    CriteriaQuery<?> query, CriteriaBuilder cb) {
+
+                return cb.like(root.get("firstname").as(String.class),
+                        String.format("%%%s%%", expression));
+            }
+        };
+    }
+
+
     private static <T> Specification<T> simplePropertySpec(
             final String property, final Object value) {
 

src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -37,6 +37,7 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.dao.DataAccessException;
+import org.springframework.dao.IncorrectResultSizeDataAccessException;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageImpl;
 import org.springframework.data.domain.PageRequest;
@@ -469,6 +470,24 @@ public class UserRepositoryTests {
     }
 
 
+    @Test
+    public void returnsNullIfNoEntityFoundForSingleEntitySpecification()
+            throws Exception {
+
+        flushTestUsers();
+        assertThat(repository.findOne(userHasLastname("Beauford")),
+                is(nullValue()));
+    }
+
+
+    @Test(expected = IncorrectResultSizeDataAccessException.class)
+    public void throwsExceptionForUnderSpecifiedSingleEntitySpecification() {
+
+        flushTestUsers();
+        repository.findOne(userHasFirstnameLike("e"));
+    }
+
+
     @Test
     public void executesCombinedSpecificationsCorrectly() {