Question

I’m looking for the best solution to store Java EE application’s global data using Hibernate. It will consist of key value pairs. Example:

projectStarted = "10-11-11"
developerNumber = 3
teamLeader = "John"

As you see, all of this entries have different types.

For now I see two options:

1) Create GlobalData entity. Each field of it will be represented as unique column in the table and will contain unique setting. This way I have no problems with type casting, but I would like to avoid it in case where there will be big amount of settings.

2) Create Setting entity. Each of it will contain two fields: key(Primary key) and value and will be represented as unique record in the table. This is preferable solution, but It’s seems to me that I will get a lot of type casting, because settings can be any type.

So basically, I’m looking for the way to implement second solution without getting a lot of troubles from different types. Can anybody help me?

Thanks.

Edit 1.

Yeah, thanks Christian. Just got similar idea.

What if I will have Settings entity, which will be like:

@Entity
@Table(name = "settings")
public class Setting {

    @Column
    private String key;
    @Column
    private String value;
    @Column
    private String converterClassFullName; //example by.lugovsky.MyConverter

    //Getters, setters
}

And GlobalData class.

public class GlobalData {
    private Date projectStarted;

    private int developerNumber;

    private String teamLeader;

    Set<Setting> settings;

    //Getters and setters for all, except settings.

}

So basically my idea is to convert Setting entity before persisting/updating/ etc. I can do this in my DAO, but I was wondering, if I could annotate GlobalData class with @Entity annotation as well without creating new table. This way I can set OneToMany annotation to Setting’s set and Perform conversions in the internal @PrePersist etc. methods.

Will Hibernate allow me to do this?

Thanks again

Answer 1

You could store a Converter-Class into the db and the let it run through the given converter for a property before using the value. JSF offers Converter API:

public interface Converter{
    public Object getAsObject(FacesContext fc, UIComponent component, String value) throws ConverterException;

    public String getAsString(FacesContext fc, UIComponent component, Object obj) throws ConverterException;
}

If you have a schema with

name: String

value: String

converter: Class

then you could do something like this:

PropertyEntry pe = // Get from OR-Mapper
Converter c = (Converter) pe.getConverter().newInstance();
Object o = c.getAsObject(null, null, pe.getValue());
// use the object o instead of value

For even more coolness you could also define a field in the class which will not be persisted which you could use to hold the converted value within the object.