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I am trying to implement a JPA-based solution using Domain Driven Development and I have encoutered a use case that I did not find any solution to. I am using JPA with Hibernate and Spring Boot.

Here is a simplified example. Lets say you have a value object:

@Embeddable
public class AmountWithCurrency {
    private BigDecimal amount;

    @Embedded
    @AttributeOverride(name="id", column=@Column(name = "CURRENCY_ID"))
    private CurrencyId currencyId;

    protected AmountWithCurrency() {
        //for JPA
    }

    public AmountWithCurrency(BigDecimal amount, CurrencyId currencyId) {
        this.amount = amount;
        this.currencyId = currencyId;
    }

Where CurrencyId is another @Embeddable with just an Long id field.

Then I have an entity with two fields:

@Embedded
@AttributeOverrides({
        @AttributeOverride(name="amount", column=@Column(name = "AMOUNT1")),
})
private AmountWithCurrency amount1;

@Embedded
@AttributeOverrides({
        @AttributeOverride(name="amount", column=@Column(name = "AMOUNT2")),
})
private AmountWithCurrency amount2;

Note that I would like the two fields to share the same DB Column CURRENCY_ID in the table. Obviously, if try to use this code, I would get this exception:

Caused by: javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.MappingException: Repeated column in mapping for entity: com.MyEntity column: currency_id (should be mapped with insert="false" update="false")
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:402)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:377)
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341)

I have tried searching online and did not find any solution.

Possible solutions: Just create two distinct currency1Id and currency2Id columns in the table and map each value object to it - works, but defeats the purpose of a shared currency on both fields. I can handle the shared currency validation on entity-level, but I think this is just an unnecessary design to add extra db column if I don't want it there. Also, if I have something like PRIMARY KEY or UNIQUE constraints on the table with the column involved, things get out of control.

Perhaps some magic with entity lifecycle hooks I did not think about?

Thank you for your comments, I appreciate your time.

Josef Bodnar
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  • The repeated mapping of a column is only a problem for JPA because it does not know which of the two values to actually save in the database should they conflict. Try using `@AttributeOverride(name ="currencyId.id", column =@Column(name="CURRENCY_ID", insertable=false, updatable=false))` on either one of the embedded fields – crizzis Jan 17 '19 at 23:27
  • Hi, I tried that and still the same error message. I tried that on both fields. I also tried using the latest spring boot, did not help. Thanks for the suggestion though. – Josef Bodnar Jan 18 '19 at 10:05

1 Answers1

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FYI, I did find one way to implement this, by changing the second field to the bare amount - so internally there is only one field for currencyId. Next I made a getter for amount2 that will re-construct the full instance using the currencyId from the first amount. Something like that:

@Embedded
@AttributeOverrides({
        @AttributeOverride(name="amount", column=@Column(name = "AMOUNT1")),
})
private AmountWithCurrency amount1;

@Column
private BigDecimal amount2;

public AmountWithCurrency getAmount2(){
    return new AmountWithCurrency(amount1.getCurrencyId(), amount2);
}

This is still not perfect solution since this still can cause issues in queries, etc. But seems to be working for me at the moment. Hope it helps someone.

Josef Bodnar
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