Hibernate Blog: Table per subclass

Table per subclass

By this strategy, you can represent inheritance relationship as a relational foreign key associations. Every class (including abstract class) has its own database table. table contains coulumns only for properties declared by subclass itself and primary key of the sub class table is also a foreign key of the superclass table.

Again, we follow the same example which we referred in my previous post with some modification, we have added the identifier properties to both classes CreditCardDetails and BankAccountDetails and marked superclass as abstract.

public abstract class CreditCardHolder {

private Long creditCardHolderId;

private String owner;

//generate getters and setters method for above properties

}

public class CreditCardDetails extends CreditCardHolder {

private Long creditCardId;

private String number;

private String expMonth;

private String expYear;

//generate getters and setters method for above properties

}

public class BankAccountDetails extends CreditCardHolder {

private Long bankAccountId;

private String account;

private String bankName;

//generate getters and setters method for above properties

}

also we have modified the CreditCardHolder.hbm.xml file. Now, there is no need to mentioned discriminator column in the database table.

<hibernate-mapping package="table.per.subclass">

</id>

<joined-subclass name="CreditCardDetails" table="CREDIT_CARD_DETAILS">

</joined-subclass>

<joined-subclass name="BankAccountDetails" table="BANK_ACCOUNT_DETAILS">

</joined-subclass>

</class>

</hibernate-mapping>

if you run the following code,

public class HibernateTest {

private final static Logger LOGGER = Logger.getLogger(HibernateTest.class);

/**

* @param args

public static void main(String[] args) {

LOGGER.info("starting of main method");

Session session = HibernateUtil.getSessionFactory().openSession();

Transaction txn = session.beginTransaction();

CreditCardDetails creditCard = new CreditCardDetails();

creditCard.setNumber("3423243234342");

creditCard.setOwner("Sachin Sharma");

creditCard.setExpMonth("10/18");

creditCard.setExpYear("2018");

BankAccountDetails bankAccountDetails = new BankAccountDetails();

bankAccountDetails.setAccount("saving");

bankAccountDetails.setBankName("SBI");

bankAccountDetails.setOwner("Sachin Sharma");

session.saveOrUpdate(creditCard);

session.saveOrUpdate(bankAccountDetails);

txn.commit();

session.close();

HibernateUtil.shutDown();

}

Now, value of the superclass properties are saved in the superclass table and value of the subclass properties are saved in the subclass tables. two row are linked together by their shared primary key value.

subclass instances should be retrieve by joining the sublcass table with superclass table.\

The advantage of this strategy is , the schema is normalized.

See the hibernate generated SQL statements as follows :

11:55:05,277 INFO HibernateTest:20 - starting of main method

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Environment <clinit>

INFO: Hibernate 3.0rc1

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Environment <clinit>

INFO: hibernate.properties not found

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Environment <clinit>

INFO: using CGLIB reflection optimizer

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Environment <clinit>

INFO: using JDK 1.4 java.sql.Timestamp handling

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration configure

INFO: configuring from resource: /hibernate.cfg.xml

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration getConfigurationInputStream

INFO: Configuration resource: /hibernate.cfg.xml

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration addResource

INFO: Mapping resource: table/per/subclass/CreditCardHolder.hbm.xml

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.HbmBinder bindRootPersistentClassCommonValues

INFO: Mapping class: table.per.subclass.CreditCardHolder -> CREDITCARDHOLDER

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.HbmBinder bindJoinedSubclass

INFO: Mapping joined-subclass: table.per.subclass.CreditCardDetails -> CE_CREDIT_CARD_DETAILS

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.HbmBinder bindJoinedSubclass

INFO: Mapping joined-subclass: table.per.subclass.BankAccountDetails -> CE_BANK_ACCOUNT_DETAILS

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration doConfigure

INFO: Configured SessionFactory: null

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration secondPassCompile

INFO: processing extends queue

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration secondPassCompile

INFO: processing collection mappings

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration secondPassCompile

INFO: processing association property references

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.Configuration secondPassCompile

INFO: processing foreign key constraints

Oct 16, 2012 11:55:05 AM org.hibernate.dialect.Dialect <init>

INFO: Using dialect: org.hibernate.dialect.MySQLDialect

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.SettingsFactory buildSettings

INFO: Maximum outer join fetch depth: 2

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.SettingsFactory buildSettings

INFO: Default batch fetch size: 1

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.SettingsFactory buildSettings

INFO: Generate SQL with comments: disabled

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.SettingsFactory buildSettings

INFO: Order SQL updates by primary key: disabled

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.SettingsFactory createQueryTranslatorFactory

INFO: Query translator: org.hibernate.hql.ast.ASTQueryTranslatorFactory

Oct 16, 2012 11:55:05 AM org.hibernate.hql.ast.ASTQueryTranslatorFactory <init>

INFO: Using ASTQueryTranslatorFactory

Oct 16, 2012 11:55:05 AM org.hibernate.cfg.SettingsFactory buildSettings

INFO: Query language substitutions: {}

Oct 16, 2012 11:55:05 AM org.hibernate.connection.C3P0ConnectionProvider configure

INFO: C3P0 using driver: null at URL: jdbc:mysql://localhost:3306/HibernateTest

Oct 16, 2012 11:55:05 AM org.hibernate.connection.C3P0ConnectionProvider configure

INFO: Connection properties: {autocommit=true, password=****, user=root}

Oct 16, 2012 11:55:05 AM org.hibernate.connection.C3P0ConnectionProvider configure

INFO: autocommit mode: true

Oct 16, 2012 11:55:05 AM org.hibernate.connection.C3P0ConnectionProvider configure

WARNING: No JDBC Driver class was specified by property hibernate.connection.driver_class

11:55:05,562 INFO MLog:80 - MLog clients using log4j logging.

11:55:05,806 INFO C3P0Registry:204 - Initializing c3p0-0.9.1.2 [built 21-May-2007 15:04:56; debug? true; trace: 10]

11:55:05,863 INFO AbstractPoolBackedDataSource:462 - Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@b0203cb4 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@8e8a79c7 [ acquireIncrement -> 1, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1bs1yqt8qsxalh4mtgoze|e40317, idleConnectionTestPeriod -> 3000, initialPoolSize -> 5, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 300, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 100, maxStatementsPerConnection -> 0, minPoolSize -> 5, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@af526d1c [ description -> null, driverClass -> null, factoryClassLocation -> null, identityToken -> 1bs1yqt8qsxalh4mtgoze|1d4b0e9, jdbcUrl -> jdbc:mysql://localhost:3306/HibernateTest, properties -> {autocommit=true, password=******, user=******} ], preferredTestQuery -> null, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, factoryClassLocation -> null, identityToken -> 1bs1yqt8qsxalh4mtgoze|1be098f, numHelperThreads -> 3 ]