Persisting recursive relationships with Hibernate

README.md

Persist Recursive relationships with Hibernate

Example on how to persist recursive relationships with Hibernate, using in this case a UUIDGenerator.

DatabaseTestModule.java

package org.hibernate.test;

import com.google.inject.AbstractModule;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import com.google.inject.persist.PersistService;
import com.google.inject.persist.jpa.JpaPersistModule;

public class DatabaseTestModule extends AbstractModule {

    @Override
    protected void configure() {
        install(new JpaPersistModule("default"));
        bind(JPAInitializer.class).asEagerSingleton();
    }

    @Singleton
    public static class JPAInitializer {

        @Inject
        public JPAInitializer(final PersistService service) {
            service.start();
        }

    }

}

Node.java

package org.hibernate.test;

import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.ToString;
import org.hibernate.annotations.GenericGenerator;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import java.util.List;

@Data
@Entity
@Table(name = "node")
@ToString(exclude = {"parent"})
@EqualsAndHashCode(of = {"uuid"})
public class Node {

    @Id
    @GeneratedValue(generator = "uuid")
    @GenericGenerator(name = "uuid", strategy = "org.hibernate.id.UUIDGenerator")
    @Column(name = "uuid")
    private String uuid;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "parent", referencedColumnName = "uuid")
    private Node parent;

    @OneToMany(mappedBy = "parent", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private List<Node> children;

}

persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
   http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
             version="2.0">

  <persistence-unit name="default" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <properties>
      <property name="hibernate.archive.autodetection" value="class" />
      <property name="hibernate.hbm2ddl.auto" value="create"/>
      <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
      <property name="hibernate.connection.driver_class" value="org.h2.Driver"/>
      <property name="hibernate.connection.url" value="jdbc:h2:./recursion-test" />
      <property name="hibernate.connection.user" value="admin" />
    </properties>
  </persistence-unit>

</persistence>

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>hibernate.test</groupId>
  <artifactId>test-recursion</artifactId>
  <version>1.0-SNAPSHOT</version>

  <description>Example to show how to persist recursive relationships with Hibernate.</description>

  <developers>
    <developer>
      <name>Jan-Willem Gmelig Meyling</name>
      <email>jan-willem@youngmediaexperts.nl</email>
    </developer>
  </developers>

  <properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <hibernate.version>5.1.0.Final</hibernate.version>
    <guice.version>4.0</guice.version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-core</artifactId>
      <version>${hibernate.version}</version>
    </dependency>
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-entitymanager</artifactId>
      <version>${hibernate.version}</version>
    </dependency>
    <dependency>
      <groupId>com.h2database</groupId>
      <artifactId>h2</artifactId>
      <version>1.4.191</version>
    </dependency>
    <dependency>
      <groupId>com.google.inject</groupId>
      <artifactId>guice</artifactId>
      <version>${guice.version}</version>
    </dependency>
    <dependency>
      <groupId>com.google.inject.extensions</groupId>
      <artifactId>guice-persist</artifactId>
      <version>${guice.version}</version>
    </dependency>
    <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <version>1.16.6</version>
      <scope>provided</scope>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.hamcrest</groupId>
      <artifactId>hamcrest-library</artifactId>
      <version>1.3</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.jukito</groupId>
      <artifactId>jukito</artifactId>
      <version>1.4.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>


</project>

RecursiveDependencyTest.java

package org.hibernate.test;

import com.google.inject.persist.Transactional;
import org.jukito.JukitoRunner;
import org.jukito.UseModules;
import org.junit.Test;
import org.junit.runner.RunWith;

import javax.inject.Inject;
import javax.persistence.EntityManager;
import java.util.ArrayList;
import java.util.List;

import static org.junit.Assert.assertThat;
import static org.hamcrest.Matchers.iterableWithSize;

@RunWith(JukitoRunner.class)
@UseModules(DatabaseTestModule.class)
public class RecursiveDependencyTest {

    @Inject EntityManager entityManager;

    @Test
    @Transactional
    public void testBiDirectionalPersistenceWithUUIDGenerator() throws Exception {
        Node parent = new Node();
        Node child = new Node();

        // Add child to parents children
        List<Node> parentsChildren = new ArrayList<>();
        parentsChildren.add(child);
        parent.setChildren(parentsChildren);
        // Set back reference as well
        child.setParent(parent);

        entityManager.persist(parent);

        assertThat(parent.getChildren(), iterableWithSize(1));
    }

}