Merge pull request #5655 from asturcon/string-cast-jpa

BAEL-2239 - JPA error "java.lang.String cannot be cast to [Ljava.lang.String;"

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/stringcast/DummyEntity.java

@@ -0,0 +1,44 @@
+package com.baeldung.jpa.stringcast;
+
+import javax.persistence.*;
+
+@SqlResultSetMapping(name = "textQueryMapping", classes = {
+  @ConstructorResult(targetClass = DummyEntity.class, columns = {
+    @ColumnResult(name = "text")
+  })
+})
+@Entity
+@Table(name = "dummy")
+public class DummyEntity {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String text;
+
+    public DummyEntity() {
+
+    }
+
+    public DummyEntity(String text) {
+        this.text = text;
+    }
+
+    public String getText() {
+        return text;
+    }
+
+    public void setText(String text) {
+        this.text = text;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/stringcast/QueryExecutor.java

@@ -0,0 +1,41 @@
+package com.baeldung.jpa.stringcast;
+
+import com.sun.istack.internal.Nullable;
+
+import javax.persistence.EntityManager;
+import javax.persistence.Query;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class QueryExecutor {
+
+    public static List<String[]> executeNativeQueryNoCastCheck(String statement, EntityManager em) {
+        Query query = em.createNativeQuery(statement);
+        return query.getResultList();
+    }
+
+    public static List<String[]> executeNativeQueryWithCastCheck(String statement, EntityManager em) {
+        Query query = em.createNativeQuery(statement);
+        List results = query.getResultList();
+
+        if (results.isEmpty()) {
+            return new ArrayList<>();
+        }
+
+        if (results.get(0) instanceof String) {
+            return ((List<String>) results)
+              .stream()
+              .map(s -> new String[] { s })
+              .collect(Collectors.toList());
+        } else {
+            return (List<String[]>) results;
+        }
+    }
+
+    public static <T> List<T> executeNativeQueryGeneric(String statement, String mapping, EntityManager em) {
+        Query query = em.createNativeQuery(statement, mapping);
+        return query.getResultList();
+    }
+
+}

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

@@ -20,6 +20,21 @@
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
         </properties>
     </persistence-unit>
+
+    <persistence-unit name="jpa-h2">
+        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+        <class>com.baeldung.jpa.stringcast.DummyEntity</class>
+        <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"/>
+        </properties>
+    </persistence-unit>
     
     <persistence-unit name="jpa-db">
         <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>

persistence-modules/java-jpa/src/test/java/com/baeldung/jpa/stringcast/SpringCastUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.jpa.stringcast;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.EntityTransaction;
+import javax.persistence.Persistence;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class SpringCastUnitTest {
+
+    private static EntityManager em;
+    private static EntityManagerFactory emFactory;
+
+    @BeforeClass
+    public static void setup() {
+        emFactory = Persistence.createEntityManagerFactory("jpa-h2");
+        em = emFactory.createEntityManager();
+
+        // insert an object into the db
+        DummyEntity dummyEntity = new DummyEntity();
+        dummyEntity.setText("text");
+
+        EntityTransaction tr = em.getTransaction();
+        tr.begin();
+        em.persist(dummyEntity);
+        tr.commit();
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenExecutorNoCastCheck_whenQueryReturnsOneColumn_thenClassCastThrown() {
+        List<String[]> results = QueryExecutor.executeNativeQueryNoCastCheck("select text from dummy", em);
+
+        // fails
+        for (String[] row : results) {
+            // do nothing
+        }
+    }
+
+    @Test
+    public void givenExecutorWithCastCheck_whenQueryReturnsOneColumn_thenNoClassCastThrown() {
+        List<String[]> results = QueryExecutor.executeNativeQueryWithCastCheck("select text from dummy", em);
+        assertEquals("text", results.get(0)[0]);
+    }
+
+    @Test
+    public void givenExecutorGeneric_whenQueryReturnsOneColumn_thenNoClassCastThrown() {
+        List<DummyEntity> results = QueryExecutor.executeNativeQueryGeneric("select text from dummy", "textQueryMapping", em);
+        assertEquals("text", results.get(0).getText());
+    }
+
+}

persistence-modules/java-jpa/src/test/resources/persistence.xml

@@ -17,5 +17,21 @@
 			<property name="hibernate.show_sql" value="true" />
 		</properties>
 	</persistence-unit>
+
+	<persistence-unit name="jpa-h2">
+		<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+		<class>com.baeldung.jpa.stringcast.DummyEntity</class>
+		<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"/>
+		</properties>
+	</persistence-unit>
+
 </persistence>