Bael 4788: Completed Article - Hibernate addScalar() method (#11783)

* BAEL-4788: Added ScalarDemo Class for Hibernate addScalar Method article

* BAEL-4788: Added unit tests in the article

* BAEL-4788: removed redundant code

Co-authored-by: Vikas Ramsingh Rajput <vikas.rajput@crownconsult.com>

persistence-modules/hibernate-queries/src/main/java/com/baeldung/hibernate/scalarmethod/HibernateScalarExample.java

@@ -0,0 +1,47 @@
+package com.baeldung.hibernate.scalarmethod;
+
+import java.util.List;
+
+import org.hibernate.Session;
+import org.hibernate.type.StandardBasicTypes;
+
+public class HibernateScalarExample {
+
+    private Session session;
+
+    public HibernateScalarExample(Session session) {
+        this.session = session;
+    }
+
+    public List<Object[]> fetchColumnWithNativeQuery() {
+        return session.createNativeQuery("SELECT * FROM Student student")
+          .list();
+    }
+
+    public List<Object[]> fetchColumnWithScalar() {
+        return session.createNativeQuery("SELECT * FROM Student student")
+          .addScalar("studentId", StandardBasicTypes.LONG)
+          .addScalar("name", StandardBasicTypes.STRING)
+          .addScalar("age", StandardBasicTypes.INTEGER)
+          .list();
+    }
+
+    public List<String> fetchLimitedColumnWithScalar() {
+        return session.createNativeQuery("SELECT * FROM Student student")
+          .addScalar("name", StandardBasicTypes.STRING)
+          .list();
+    }
+
+    public List<Object[]> fetchColumnWithOverloadedScalar() {
+        return session.createNativeQuery("SELECT * FROM Student student")
+          .addScalar("name", StandardBasicTypes.STRING)
+          .addScalar("age")
+          .list();
+    }
+
+    public Integer fetchAvgAgeWithScalar() {
+        return (Integer) session.createNativeQuery("SELECT AVG(age) as avgAge FROM Student student")
+          .addScalar("avgAge")
+          .uniqueResult();
+    }
+}

persistence-modules/hibernate-queries/src/test/java/com/baeldung/hibernate/scalarmethod/HibernateScalarExampleUnitTest.java

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+package com.baeldung.hibernate.scalarmethod;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Random;
+
+import org.hibernate.Session;
+import org.hibernate.Transaction;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import com.baeldung.hibernate.HibernateUtil;
+import com.baeldung.hibernate.pojo.Student;
+
+public class HibernateScalarExampleUnitTest {
+
+    private static Session session;
+    private static Transaction transaction;
+    private static final int DATA_SIZE = 50000;
+    private static HibernateScalarExample scalarExample;
+
+    @BeforeClass
+    public static void setUp() throws IOException {
+        session = HibernateUtil.getSessionFactory().openSession();
+        transaction = session.beginTransaction();
+        scalarExample = new HibernateScalarExample(session);
+        session.createNativeQuery("delete from Student").executeUpdate();
+        for (int i = 0; i < DATA_SIZE; i++) {
+            Student student = new Student("John-" + i, generateRandomAge(5, 24));
+            session.persist(student);
+        }
+        transaction.commit();
+        transaction = session.beginTransaction();
+    }
+
+    @AfterClass
+    public static void tearDown() {
+        transaction.rollback();
+        session.close();
+    }
+
+    @Test
+    public void givenNativeQuery_whenNoScalarUsed_ThenFetchAll() {
+        List<Object[]> list = scalarExample.fetchColumnWithNativeQuery();
+        assertEquals(DATA_SIZE, list.size());
+    }
+
+    @Test
+    public void givenNativeQuery_whenScalarUsed_ThenFetchAll() {
+        List<Object[]> list = scalarExample.fetchColumnWithScalar();
+        assertEquals(DATA_SIZE, list.size());
+    }
+
+    @Test
+    public void givenNativeQuery_whenScalarUsed_ThenFetchLimitedColumns() {
+        List<String> list = scalarExample.fetchLimitedColumnWithScalar();
+        for (String colValue : list) {
+            assertTrue(colValue.startsWith("John"));
+        }
+    }
+
+    @Test
+    public void givenNativeQuery_whenScalarUsedForSingleResult_ThenSingleValueReturned() {
+        List<Object[]> list = scalarExample.fetchColumnWithOverloadedScalar();
+        for (Object[] colArray : list) {
+            assertEquals(2, colArray.length);
+        }
+    }
+
+    @Test
+    public void whenScalarUsedForAvgAge_ThenSingleValueReturned() {
+        Integer avgAge = scalarExample.fetchAvgAgeWithScalar();
+        assertEquals(true, (avgAge >= 5 && avgAge <= 24));
+    }
+
+    private static int generateRandomAge(int min, int max) {
+        return new Random().nextInt(max - min + 1) + min;
+    }
+}