Hibernate: Mapping toString() class method to String db column

Question

I have 2 classes A and C of this kind

@Entity
@Table(name = "A")
public class A
{
    private int id;
    private String b;
    private C c;

    // Getters & Setters with @Column annotation
}

public class C
{
    private String d;
    private String e;

    // Getters & Setters ...

    public String toString() {...}
    public boolean fromString(String serializedC){ ... }
}

and a db table like this

CREATE TABLE A
{
    INT id NOT NULL,
    VARCHAR(64) b,
    TEXT c
};

I would like to store the whole C element within c column thanks to the toString() method and read it from the database thx to the fromString() one. Is there any way to achieve it easily with an hibernate mapping?

vp8106 · Accepted Answer · 2014-09-15 07:51:15Z

The easiest way is to define getter/setter in class A that will call C.toString() and C.fromString() like so:

@Entity
@Table(name = "A")
public class A {

    private int id;
    private String b;
    private C c;

    @Id
    @Column
    public int getId() {
        return id;
    }

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

    @Column
    public String getB() {
        return b;
    }

    public void setB(String b) {
        this.b = b;
    }

    @Transient
    public C getC() {
        return c;
    }
    public void setC(C c) {
        this.c = c;
    }

    @Column
    protected String getCAsString() {
        return c!=null? c.toString() : null;
    }
    protected void setCAsString(String c) {
        this.c = new C();
        this.c.fromString(c);
    }        
}

Note: mark getC() with @Transient annotation as it is not intended to be mapped to any column.

Xstian · Accepted Answer · 2014-09-10 08:56:16Z

I suggest you JAXB.. you can see this tutorial .

In newInstance you must add the class root element that map your xml... below an example

Here an example ..

public static void main(String[] args) throws JAXBException {
        final JAXBContext context = JAXBContext.newInstance(Vehicals.class);
        final Marshaller m = context.createMarshaller();
        m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

        final Vehicals vehicals = new Vehicals();

        List<Car> cars = new ArrayList<Car>();
        Car c = new Car();
        c.setName("Mercedes");
        cars.add(c);

        c = new Car();
        c.setName("BMW");
        cars.add(c);

        vehicals.setCar(cars);

        m.marshal(vehicals, System.out);
    }

Vehicals.java

import java.util.List;

import javax.xml.bind.annotation.XmlRootElement;

    @XmlRootElement
    public class Vehicals {

        private List<Car> Car;

        public List<Car> getCar() {
            return Car;
        }

        public void setCar(List<Car> cars) {
            this.Car = cars;
        }
    }

Car.java

import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlTransient;

@XmlRootElement
public class Car {

    @XmlTransient
    private Long id;

    private String name;

    @XmlTransient
    private String code;


    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getCode() {
        return code;
    }
    public void setCode(String code) {
        this.code = code;
    }
}

output.xml

<Vehicle>
     <Car>
         <name>Mercedes</name>
      </Car> 
     <Car>
         <name>BMW</name>
     </Car>
</Vehicle>

Boris Pavlović · Accepted Answer · 2014-09-10 12:20:01Z

0

Take a look at the 2 minute tutorial on XStream

The easiest thing is to change the type of the c field in the class A from C to String

Then use the XStream from the rest of the code to transform an object of C to XML string and transform it back to C when getting it from an object of type A.

EDIT: Hibernate Custom Types are the way to go to serialize a string encoded version of C in a database. Take a look at this tutorial: http://blog.xebia.com/2009/11/09/understanding-and-writing-hibernate-user-types/

edited Sep 10, 2014 at 12:20

answered Sep 10, 2014 at 8:40

Boris Pavlović

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1 Comment

Ste Over a year ago

Actually, in my mind I would use xstream inside toString() and fromString() methods of class C. There's no easy way to tell Hibernate to use C.toString() and C.fromString() methods while mapping C to the TEXT db column?

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