Integrating JPA Hibernate with OptaPlanner

We’ve been improving the integration of OptaPlanner with the rest of JEE,
so it’s easier to build end user applications that just work.
Let’s take a look at the improved JPA Hibernate integration.

The basics

Both JPA Hibernate and OptaPlanner work on POJO’s (Plain Old Java Objects),
so just add some JPA annotations on your domain objects to persist them with JPA Hibernate
and add some OptaPlanner annotations to solve your optimization problem with OptaPlanner.

On each problem fact class, there are usually only JPA annotations:

@Entity // JPA annotation
public class Computer {

    private int cpuPower;
    private int memory;
    private int networkBandwidth;
    private int cost;

    ...
}

On each planning entity class, there are both JPA and OptaPlanner annotations:

@PlanningEntity // OptaPlanner annotation
@Entity // JPA annotation
public class Process {

    private int requiredCpuPower;
    private int requiredMemory;
    private int requiredNetworkBandwidth;

    @PlanningVariable(...) // OptaPlanner annotation
    @ManyToOne() // JPA annotation
    private Computer computer;

    ...
}

Don’t confuse a JPA entity (anything object that gets persisted in the database)
with an OptaPlanner planning entity (an object that gets changed by OptaPlanner during solving).

Persisting a score

By default, JPA Hibernate will put a Score in a BLOB column through Java serialization.
This is undesirable because it prevents using the score in a JPA-QL query.
Furthermore, it triggers database issues when upgrading the OptaPlanner version.

Therefore, OptaPlanner 6.4.0.Beta1 has a new jar optaplanner-persistence-jpa that contains a Hibernate type for each score type.
Use it like this:

@PlanningSolution // OptaPlanner annotation
@Entity // JPA annotation
@TypeDef(defaultForType = HardSoftScore.class, typeClass = HardSoftScoreHibernateType.class) // Hibernate annotation
public class CloudBalance implements Solution<HardSoftScore> {

    @Columns(columns = {@Column(name = "hardScore"), @Column(name = "softScore")}) // JPA annotation
    private HardSoftScore score;

    ...
}

This puts the HardSoftScore into 2 INTEGER columns, instead of a BLOB column.
The OptaPlanner reference manual contain more information on how to deal with BigDecimal and/or bendable scores properly.

Cloning pitfall

In a JPA model it’s common that the problem facts reference the planning solution,
which can corrupt planning cloning (if the default planning cloner is used).

To overcome this, simply annotate the problem fact classes that reference the planning solution or a planning entity
with a @DeepPlanningClone annotation:

@DeepPlanningClone // OptaPlanner annotation: Force the default planning cloner to planning clone this class too
@Entity // JPA annotation
public class Computer {

    @ManyToOne
    private CloudBalance cloudBalance;

    ...
}

This way, the Computer class is planning cloned too and the clone’s cloudBalance field will point to the CloudBalance clone.

Conclusion

You can use the same domain classes for JPA Hibernate and OptaPlanner, there is no need duplicate your domain!

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