Conversion between DB data and java data ?

[Sol Mayer-Orn]

Hi,

I've just started using JPA, and would appreciate it if anyone could help with the following question:

What is the recommended way to define a conversion rule between my database data, and my Java data ?
For example, say my (badly designed) database stores string values of "YES" and "NO", which I'd like to convert to java boolean :

Table "SUBSCRIPTION":    
---------------------------------
|  ID   |   IS_MONTHLY 
---------------------------------
|   1   |    'YES'         
|   2   |    'NO'         
|   2   |    'NO'         
---------------------------------
 
Java class:
@Entity public class Subscription {
     @Id  private long id;
     private boolean isMonthly;
     ...
}

What is the most recommended way to do the conversion ?
Thanks
[ September 30, 2007: Message edited by: Sol Mayer-Orn ]

[Edvins Reisons]

Not sure that you can do this directly in JPA. With a bit of flexibility, though, either on the Java side (use an enum) or on the DB side (change the column type to whatever a boolean is persisted to), I think one can move forward here.

[Sol Mayer-Orn]

Thanks very much

[James Sutherland]

The most portable way to define the conversion is to use property access for the class and define get/set methods that convert the value.

i.e.
public class Subscription {
..
@Transient
public boolean isMonthly() {
return isMonthly;
}
public void setIsMonthly(boolean isMonthly) {
this.isMonthly = isMonthly;
}
@Basic
private String getMonthlyString() {
if (isMonthly() {
return "Yes";
} else {
return "No";
}
}
private String setMonthlyString(String value) {
setIsMonthly(value.eqauls("Yes"));
}
}

However most JPA implementation have extended conversion support. If you are using TopLink (or TopLink Essentials, or EclipseLink) you can use a Converter on your mapping. In TopLink 11g you can use the @ObjectTypeConverter and @Convert annotations for this.

If you are using Hibernate you can use their custom type system and their @Type annotation.