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POHow to persist initial data with JpaRepository
 

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  1. POHow to persist initial data with JpaRepository
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    <p>In order to initially fill the database with data, I created entity instances and wrote a service class that should save them in the database.</p> <p>In a very simplified way, my model consists of three classes A, B and C. The instances of the classes A and B both reference (the same) instances of C (annotated with <code>@ManyToOne</code>):</p> <pre><code>a1 -&gt; c1 a2 -&gt; c2 a3 -&gt; c1 b1 -&gt; c1 b2 -&gt; c2 </code></pre> <p>For A and B I use <code>JpaRepositories</code> for persistence.</p> <p>Then I try to save the instances I created programmatically:</p> <pre><code>@Transactional public void save(A a1, A a2, A a3, B b1, B b2) { aRepo.save(a1); aRepo.save(a2); aRepo.save(a3); bRepo.save(b1); bRepo.save(b2); } </code></pre> <p>I get an exception ("detached entity passed to persist: C") in the third line, because the instance c1 got saved already in the first line. </p> <p>How can I avoid that? I thought that marking my save method in my service with <code>@Transactional</code> would be sufficient already, but obviously it's not.</p> <p>Of course I could just write </p> <pre><code>aRepo.save(Arrays.asList(a1, a2, a3)); bRepo.save(Arrays.asList(b1, b2)); </code></pre> <p>but that only shifts my problem as the exception then occurs in the second line when the b1 that references the already saved c1 should get saved.</p> <p>How can I save the data structures I created in one method without getting that exception?</p> <p>Here's the rest of the code:</p> <pre><code>@Entity public class A { @Id @GeneratedValue @Access(AccessType.FIELD) private Long id; @ManyToOne(cascade = CascadeType.ALL) @Access(AccessType.FIELD) private C c; public A(C c) { this.c = c; } public C getC() { return c; } } </code></pre> <p>Class B looks exactly the same, class C only contains the ID parameter.</p> <p>The instances are created within a test case:</p> <pre><code>public class DBTest extends AbstractH2TestCase { @Test public void testDataStorage() { final AbstractApplicationContext context = new AnnotationConfigApplicationContext(DBTest.class); try { final PersistService persistService = context.getBean(PersistService.class); C c1 = new C(); C c2 = new C(); A a1 = new A(c1); A a2 = new A(c2); A a3 = new A(c1); B b1 = new B(c1); B b2 = new B(c2); persistService.save(b1, b2, a1, a2, a3); } finally { context.close(); } } } </code></pre> <p>The superclass for the test I found somewhere on the web and modified it a bit:</p> <pre><code>@Configuration @ComponentScan(basePackageClasses = A.class) @EnableJpaRepositories public class AbstractH2TestCase { public AbstractH2TestCase() { super(); } @Bean public DataSource dataSource() { return new EmbeddedDatabaseBuilder().setType(H2).build(); } @Bean public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) { final LocalContainerEntityManagerFactoryBean lef = new LocalContainerEntityManagerFactoryBean(); lef.setDataSource(dataSource); lef.setJpaVendorAdapter(jpaVendorAdapter); final String thisPackageAndSubpackages = this.getClass().getPackage().getName(); lef.setPackagesToScan(thisPackageAndSubpackages); return lef; } @Bean public JpaVendorAdapter jpaVendorAdapter() { final HibernateJpaVendorAdapter hibernateJpaVendorAdapter = new HibernateJpaVendorAdapter(); hibernateJpaVendorAdapter.setShowSql(false); hibernateJpaVendorAdapter.setGenerateDdl(true); hibernateJpaVendorAdapter.setDatabase(Database.H2); return hibernateJpaVendorAdapter; } @Bean public PlatformTransactionManager transactionManager() { return new JpaTransactionManager(); } } </code></pre> <p>If you want a running version of the code - I checked it in here:</p> <p><a href="https://github.com/BernhardBln/stackexchange" rel="nofollow">https://github.com/BernhardBln/stackexchange</a></p> <p>It's a maven project.</p>
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    1. COCould you show the code that initializes the instances of a1-3 and c1, c2?
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    2. COI added it, plus a link to github where I put a running example
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