Spring batch Custom itemWriter with insert or update mechanism

Question

I have Spring Batch with a basic chunk:

1. Read a CSV file.
2. Process it (Transcode some coded value into another ones).
3. Write the result into a database.

The problem

In some case, I want insert or update mechnism in my custom ItemWriter.

Exemple: I can get this 2 lines on my CSV

C006;Test;OK;01/01/1970;1
C006;Test;OK;01/01/1970;5

You can figure out that they are pretty similar except the last column, the strategy will be:

1. Check the database if I have a "like so" entity
2. if true, update the value with the last item that you get (in our case, the second line with the value 5 in the last column)

What I already did?

In my entity bean, I added a Unique Constraint anotation like so:

@Table(name = "indicator",
    uniqueConstraints = { @UniqueConstraint(columnNames = 
                                        { "reference", "type", "status", "date" }) })

I'm sure now that I cannot persist an entity with the same column's data. Then, I created a custom ItemWriter, and I tried to catch the ConstraintViolationException but it didn't work, I always get an other exeption, even when I tried the parent one.

So do you have any ideas or another way to do it?

I was think about using merge JPA functionality? what do you think about it?

My custom ItemWriter

@Component
public class ImportItemWriter implements ItemWriter<Indicator>{

    @Autowired
    protected IndicatorDao indicatorDao;

    public void write(List<? extends Indicator> items) throws Exception {

        for (Indicator item : items) {
            Indicator indicator = new Indicator();

            indicator.setReference(item.getReference());
            indicator.setType(item.getType());
            indicator.setStatus(item.getStatus());
            indicator.setDueDate(item.getDueDate());

            indicator.setValue(item.getValue());

            try {
                indicatorDao.persist(indicator);
            } catch (ConstraintViolationException e) {
                // TODO: handle exception
            }       
        }
    }
}

Update Problem Solved The idea of using Composite PKey is interesting, but I can't use it because I have to create a composite with 9 keys that's not fair in term of performance. I decided to add function to my DAO (isDuplicated) and in my custom ItemWriter, I just make a simple test:

if `isDuplicated()` then `updateEntity()` else `insertNew()`

Answer 1

One option would be to use the ClassifierCompositeItemWriter. The Classifier would be used to determine whether to do the insert or the update. Then you'd configure two delegates, one for inserts, one for updates.

Answer 2

Summarize the above comments.

Have you thought about using this directly? .. the implementation performs a entityManger.merge(..) .. if your entity have a composite pkey you could solve in this way.

    <job id="writeProductsJob" xmlns="http://www.springframework.org/schema/batch">
        <step id="readWrite">
            <tasklet>
                <chunk reader="productItemReader" writer="productItemWriter" commit-interval="3" />
            </tasklet>
        </step>
    </job>

    <bean id="productItemWriter" class="org.springframework.batch.item.database.JpaItemWriter">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>

By an @EmbeddedId you can build a composite primary key in order to merge the entity. See this link

Entity

@Entity
@Table(name = "CAR")
public class Car {

    @EmbeddedId
    private CarPK carPK;

    @Column
    private String name;
}

Composite Primary Key

@Embeddable
public class CarPK implements Serializable {

    @Column
    private String chassisSerialNumber;

    @Column
    private String engineSerialNumber;

    public CarPK(){
        // Your class must have a no-arq constructor
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof CarPK){
            CarPK carPk = (CarPK) obj;

            if(!carPk.getChassisSerialNumber().equals(chassisSerialNumber)){
                return false;
            }

            if(!carPk.getEngineSerialNumber().equals(engineSerialNumber)){
                return false;
            }

            return true;
        }

        return false;
    }

    @Override
    public int hashCode() {
        return chassisSerialNumber.hashCode() + engineSerialNumber.hashCode();
    }

    //setter and getter
}