2.11.4. Table per class

<div class="paragraph">

A third option is to map only the concrete classes of an inheritance hierarchy to tables.
This is called the table-per-concrete-class strategy.
Each table defines all persistent states of the class, including the inherited state.

</div>
<div class="paragraph">

In Hibernate, it is not necessary to explicitly map such inheritance hierarchies.
You can map each class as a separate entity root.
However, if you wish use polymorphic associations (e.g. an association to the superclass of your hierarchy), you need to use the union subclass mapping.

</div>
<div id="entity-inheritance-table-per-class-example" class="exampleblock">
<div class="title">Example 191. Table per class</div>
<div class="content">
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight">`@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public static class Account {

    @Id
    private Long id;

    private String owner;

    private BigDecimal balance;

    private BigDecimal interestRate;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getOwner() {
        return owner;
    }

    public void setOwner(String owner) {
        this.owner = owner;
    }

    public BigDecimal getBalance() {
        return balance;
    }

    public void setBalance(BigDecimal balance) {
        this.balance = balance;
    }

    public BigDecimal getInterestRate() {
        return interestRate;
    }

    public void setInterestRate(BigDecimal interestRate) {
        this.interestRate = interestRate;
    }
}

@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {

    private BigDecimal overdraftFee;

    public BigDecimal getOverdraftFee() {
        return overdraftFee;
    }

    public void setOverdraftFee(BigDecimal overdraftFee) {
        this.overdraftFee = overdraftFee;
    }
}

@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {

    private BigDecimal creditLimit;

    public BigDecimal getCreditLimit() {
        return creditLimit;
    }

    public void setCreditLimit(BigDecimal creditLimit) {
        this.creditLimit = creditLimit;
    }
}`</pre>
</div>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight">`CREATE TABLE Account (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    PRIMARY KEY ( id )
)

CREATE TABLE CreditAccount (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    creditLimit NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)

CREATE TABLE DebitAccount (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    overdraftFee NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)`</pre>
</div>
</div>
</div>
</div>
<div class="paragraph">

When using polymorphic queries, a UNION is required to fetch the base class table along with all subclass tables as well.

</div>
<div class="exampleblock">
<div class="title">Example 192. Table per class polymorphic query</div>
<div class="content">
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight">`List&lt;Account&gt; accounts = entityManager
    .createQuery( "select a from Account a" )
    .getResultList();`</pre>
</div>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight">`SELECT tablepercl0_.id AS id1_0_ ,
       tablepercl0_.balance AS balance2_0_ ,
       tablepercl0_.interestRate AS interest3_0_ ,
       tablepercl0_.owner AS owner4_0_ ,
       tablepercl0_.overdraftFee AS overdraf1_2_ ,
       tablepercl0_.creditLimit AS creditLi1_1_ ,
       tablepercl0_.clazz_ AS clazz_
FROM (
    SELECT    id ,
             balance ,
             interestRate ,
             owner ,
             CAST(NULL AS INT) AS overdraftFee ,
             CAST(NULL AS INT) AS creditLimit ,
             0 AS clazz_
    FROM     Account
    UNION ALL
    SELECT   id ,
             balance ,
             interestRate ,
             owner ,
             overdraftFee ,
             CAST(NULL AS INT) AS creditLimit ,
             1 AS clazz_
    FROM     DebitAccount
    UNION ALL
    SELECT   id ,
             balance ,
             interestRate ,
             owner ,
             CAST(NULL AS INT) AS overdraftFee ,
             creditLimit ,
             2 AS clazz_
    FROM     CreditAccount
) tablepercl0_`</pre>
</div>
</div>
</div>
</div>
<div class="admonitionblock important">
<table>
<tr>
<td class="icon">

</td>
<td class="content">
<div class="paragraph">

Polymorphic queries require multiple UNION queries, so be aware of the performance implications of a large class hierarchy.

</div>
</td>
</tr>
</table>
</div>
</div>
</div>
<div class="sect2">