Mapped SuperClass Support

Introduction:

Mapped super class is used to define state and mapping information that is common to multiple entity classes.It is a super class which does not have any separate table.It is never be a part of persistent relationship and can be concrete or an abstract class. Kundera has now enabled Mapped super class and Inheritance strategy support with all the datastores that it currently supports.

Why Support it ?

In order to become a stronger JPA provider and enable support of traditional normalized schema Kundera has also enabled support of Mapped Superclasses and Inheritance strategy.

Mapped SuperClass as concrete class :

Sample Transaction use case

@MappedSuperclass
@Table(name = "TRNX")
public class Transaction 
{

    @Id
    private String txId;
    
    @Column
    private String bankIdentifier;

    
    @Column
    private Date transactionDt;

CreditTransaction :

@Entity
@Table(name = "TRNX_CREDIT")
@IndexCollection(columns={@Index(name="bankIdentifier")})
public class CreditTransaction extends Transaction
{

    @Column
    private Integer amount;

    @Column
    @Enumerated(EnumType.STRING)
    private Status txStatus;

DebitTransaction :

@Entity
@IndexCollection(columns={@Index(name="bankIdentifier")})
public class DebitTransaction extends Transaction
{

    @Column
    private Integer amount;

    @Column
    @Enumerated(EnumType.STRING)
    private Status txStatus;

Inheritance Strategy:

It can be implemented in two ways :

• Discriminator column
• Attribute Override

Sample Transaction Use Case :

@Entity
@Table(name = "TRNX")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "tx_type")
public class Transaction extends AbstractTransaction
{
    
    @Column
    private String bankIdentifier;

CreditTransaction :

@Entity
@Table(name = "TRNX_CREDIT")
@DiscriminatorValue(value = "CREDIT")
@AttributeOverride(name="bankIdentifier",column= @Column(name="CREDIT_BANK_IDENT"))
@IndexCollection(columns={@Index(name="bankIdentifier")})
public class CreditTransaction extends Transaction
{

    @Column
    private Integer amount;

    @Column
    @Enumerated(EnumType.STRING)
    private Status txStatus;

Debit Transaction :

@Entity
@DiscriminatorValue(value="DEBIT")
@AttributeOverrides(value = { @AttributeOverride(name = "txId", column = @Column(name = "DEBIT_ID")),
@AttributeOverride(name = "bankIdentifier", column = @Column(name = "DEBIT_BANK_IDENT")),
@AttributeOverride(name = "transactionDt", column = @Column(name = "TX_DT")) })
public class DebitTransaction extends Transaction
{

    @Column
    private Integer amount;

Entity Transaction :

        CreditTransaction creditTx = new CreditTransaction();
        creditTx.setTxId("credit1");
        creditTx.setTxStatus(Status.APPROVED);
        creditTx.setBankIdentifier("sbi");
        creditTx.setTransactionDt(new Date());
        creditTx.setAmount(10);
        em.persist(creditTx);

        waitThread(wait);

        DebitTransaction debitTx = new DebitTransaction();
        debitTx.setTxId("debit1");
        debitTx.setTxStatus(Status.PENDING);
        debitTx.setTransactionDt(new Date());
        debitTx.setBankIdentifier("sbi");
        debitTx.setAmount(-10);
        em.persist(debitTx);

Benefits :

• Mapped Superclass and inheritance Strategy enable tradition normalized relational database schema support.
• Another advantage of enabling the same is that attributes that are common to multiple persistent classes can be defined in the superclass without having to suffer the performance consequences.

To-do :

• Enable join table support