BAEL-2814 Added files for article (#6968)

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/projections/Product.java

@@ -0,0 +1,50 @@
+package com.baeldung.jpa.projections;
+
+import java.math.BigDecimal;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class Product {
+    @Id
+    private long id;
+    private String name;
+    private String description;
+    private String category;
+    private BigDecimal unitPrice;
+    
+    public long getId() {
+        return id;
+    }
+    public void setId(long id) {
+        this.id = id;
+    }
+    public String getName() {
+        return name;
+    }
+    public void setName(String name) {
+        this.name = name;
+    }
+    public String getDescription() {
+        return description;
+    }
+    public void setDescription(String description) {
+        this.description = description;
+    }
+    public String getCategory() {
+        return category;
+    }
+    public void setCategory(String category) {
+        this.category = category;
+    }
+    public BigDecimal getUnitPrice() {
+        return unitPrice;
+    }
+    public void setUnitPrice(BigDecimal unitPrice) {
+        this.unitPrice = unitPrice;
+    }
+    
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/projections/ProductRepository.java

@@ -0,0 +1,93 @@
+package com.baeldung.jpa.projections;
+
+import java.util.List;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+import javax.persistence.Query;
+import javax.persistence.Tuple;
+import javax.persistence.criteria.CriteriaBuilder;
+import javax.persistence.criteria.CriteriaQuery;
+import javax.persistence.criteria.Root;
+
+public class ProductRepository {
+    private EntityManager entityManager;
+
+    public ProductRepository() {
+        EntityManagerFactory factory = Persistence.createEntityManagerFactory("jpa-projections");
+        entityManager = factory.createEntityManager();
+    }
+    
+    @SuppressWarnings("unchecked")
+    public List<Object> findAllNamesUsingJPQL() {
+        Query query = entityManager.createQuery("select name from Product");
+        List<Object> resultList = query.getResultList();
+        return resultList;
+    }
+    
+    @SuppressWarnings("unchecked")
+    public List<Object> findAllIdsUsingJPQL() {
+        Query query = entityManager.createQuery("select id from Product");
+        List<Object> resultList = query.getResultList();
+        return resultList;
+    }
+    
+    public List<String> findAllNamesUsingCriteriaBuilder() {
+        CriteriaBuilder builder = entityManager.getCriteriaBuilder();
+        CriteriaQuery<String> query = builder.createQuery(String.class);
+        Root<Product> product = query.from(Product.class);
+        query.select(product.get("name"));
+        List<String> resultList = entityManager.createQuery(query).getResultList();
+        return resultList;
+    }
+    
+    @SuppressWarnings("unchecked")
+    public List<Object[]> findAllIdAndNamesUsingJPQL() {
+        Query query = entityManager.createQuery("select id, name from Product");
+        List<Object[]> resultList = query.getResultList();
+        return resultList;
+    }
+    
+    public List<Object[]> findAllIdAndNamesUsingCriteriaBuilderArray() {
+        CriteriaBuilder builder = entityManager.getCriteriaBuilder();
+        CriteriaQuery<Object[]> query = builder.createQuery(Object[].class);
+        Root<Product> product = query.from(Product.class);
+        query.select(builder.array(product.get("id"), product.get("name")));
+        List<Object[]> resultList = entityManager.createQuery(query).getResultList();
+        return resultList;
+    }
+    
+    public List<Object[]> findAllIdNameUnitPriceUsingCriteriaQueryMultiselect() {
+        CriteriaBuilder builder = entityManager.getCriteriaBuilder();
+        CriteriaQuery<Object[]> query = builder.createQuery(Object[].class);
+        Root<Product> product = query.from(Product.class);
+        query.multiselect(product.get("id"), product.get("name"), product.get("unitPrice"));
+        List<Object[]> resultList = entityManager.createQuery(query).getResultList();
+        return resultList;
+    }
+    
+    public List<Tuple> findAllIdAndNamesUsingCriteriaBuilderTuple() {
+        CriteriaBuilder builder = entityManager.getCriteriaBuilder();
+        CriteriaQuery<Tuple> query = builder.createQuery(Tuple.class);
+        Root<Product> product = query.from(Product.class);
+        query.select(builder.tuple(product.get("id"), product.get("name")));
+        List<Tuple> resultList = entityManager.createQuery(query).getResultList();
+        return resultList;
+    }
+    
+    public List<Object[]> findCountByCategoryUsingJPQL() {
+        Query query = entityManager.createQuery("select p.category, count(p) from Product p group by p.category");
+        return query.getResultList();
+    }
+    
+    public List<Object[]> findCountByCategoryUsingCriteriaBuilder() {
+        CriteriaBuilder builder = entityManager.getCriteriaBuilder();
+        CriteriaQuery<Object[]> query = builder.createQuery(Object[].class);
+        Root<Product> product = query.from(Product.class);
+        query.multiselect(product.get("category"), builder.count(product));
+        query.groupBy(product.get("category"));
+        List<Object[]> resultList = entityManager.createQuery(query).getResultList();
+        return resultList;
+    }
+}

persistence-modules/java-jpa/src/main/resources/META-INF/persistence.xml

@@ -147,7 +147,7 @@
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false" />
         </properties>
     </persistence-unit>
-    
+  
     <persistence-unit name="jpa-entity-definition">
         <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
         <class>com.baeldung.jpa.entity.Student</class>
@@ -163,4 +163,21 @@
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false" />
         </properties>
     </persistence-unit>
+
+    <persistence-unit name="jpa-projections">
+        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+        <class>com.baeldung.jpa.projections.Product</class>
+        <exclude-unlisted-classes>true</exclude-unlisted-classes>
+        <properties>
+            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
+            <property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:test"/>
+            <property name="javax.persistence.jdbc.user" value="sa"/>
+            <property name="javax.persistence.jdbc.password" value=""/>
+            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
+            <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
+            <property name="show_sql" value="true"/>
+            <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
+            <property name="javax.persistence.sql-load-script-source" value="products_jpa.sql"/>
+        </properties>
+    </persistence-unit>
 </persistence>

persistence-modules/java-jpa/src/main/resources/products_jpa.sql

@@ -0,0 +1,4 @@
+insert into product(id, name, description, category) values (1,'Product Name 1','This is Product 1', 'category1');
+insert into product(id, name, description, category) values (2,'Product Name 2','This is Product 2', 'category1');
+insert into product(id, name, description, category) values (3,'Product Name 3','This is Product 3', 'category2');
+insert into product(id, name, description, category) values (4,'Product Name 4','This is Product 4', 'category3');