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How to map typesafe enumerations with Castor


Intended Audience
Prerequisites
Steps
Tips


Intended Audience

Anyone who wants to persist object that refer to a typesafe enumeration.

This document addresses the basics and shows an example how to map an object that has a typesafe enumeration property.

Prerequisites

Enumerations are a common method for ensuring data integrity, both in software and in relational databases. As a platform for linking the two, we added support for persisting class fields whose type is a Java typesafe enumeration to Castor JDO.

To use this new feature your typesafe enumeration should follow the enum pattern commonly used and provide a static valueOf(String) method. An enum of different kinds of computer equipment may look like:

public class KindEnum {
    private static final Map KINDS = new HashMap();

    public static final KindEnum MOUSE = new KindEnum("Mouse");
    public static final KindEnum KEYBOARD = new KindEnum("Keyboard");
    public static final KindEnum COMPUTER = new KindEnum("Computer");
    public static final KindEnum PRINTER = new KindEnum("Printer");
    public static final KindEnum MONITOR = new KindEnum("Monitor");

    private final String _kind;

    private KindEnum(final String kind) {
        _kind = kind;
        KINDS.put(kind, this);
    }

    public static KindEnum valueOf(final String kind) {
	    return (KindEnum) KINDS.get(kind);
    }

    public String toString() { return _kind; }
}
            

At your Product class you may want to have a property that tells you what kind of computer equipment a product is of.

public class Product {
    private int         _id;
    private String      _name;
    private KindEnum    _kind;
    
    public Product() { }
    
    public int getId() { return _id; }
    public void setId(int id) { _id = id; }

    public String getName() { return _name; }
    public void setName(String name) { _name = name; }

    public KindEnum getKind() { return _kind; }
    public void setKind(KindEnum kind) { _kind = kind; }
}
            

Steps

Your mapping for the Product class should be:

<class name="Product" identity="id">
  <description>Product with kind enum</description>
  <map-to table="enum_prod"/>
  <field name="id" type="integer">
    <sql name="id" type="integer"/>
  </field>
  <field name="name" type="string">
    <sql name="name" type="char"/>
  </field>
  <field name="kind" type="KindEnum">
    <sql name="kind" type="char"/>
  </field>
</class>
            

Tips

-To add this new feature we added an additional check when searching for field types. Like before Castor first searches for know types and thereafter for a mapping for the class you specified as type. If both of them do not match it now checks if the class specified as type is available at classpath and has a static valueOf(String) method. Only if all of this conditions are met it will be viewed as a valid mapping.
 
   
  
   
 


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