Re: changing types and UDT columns

[Rick Hillegas]

Hi Kathey,

Thanks for buddy-testing this feature. Some comments inline...
Kathey Marsden wrote:
I am starting on the UDT buddy testing and am trying to understand  
what happens when a  fields change or are added to a class.

What I did was created a Price class with a single double field price, 
generated the serial version with serialver and then inserted a value 
into a table.

Then I added a String field for a currencyCode and a function to 
retrieve it.

I recompiled and tried to regenerate the serialver, which I was 
surprised stayed the same.
If you hard-coded serialVersionUID, then I would expect that serialver 
would just report that hard-coded value. Note that the javadoc for 
java.io.Serializable recommends the hygienic practice of declaring 
serialVersionUID as private.
  Then I inserted another row.
when I selected the currency code from the table, it was all pretty 
nice, and just said it was NULL for the first object.
ij> select getCurrencyCode(pr) from items;
1
----
NULL
USD

2 rows selected

So are changing types all automagical like that or is there typically 
something that needs to be done as they change?
Your example type evolution is one of the simple cases which the default 
serialization logic knows how to handle: "The version control works 
great as long as the changes are compatible. Compatible changes include 
adding or removing a method or a field. Incompatible changes include 
changing an object's hierarchy or removing the implementation of the 
Serializable interface. A complete list of compatible and incompatible 
changes is given in the Java Serialization Specification." That quote 
comes from this web page: 
http://java.sun.com/developer/technicalArticles/Programming/serialization/

Hope this helps,
-Rick

 Below is the sql and final Price class.  The first version just had 
the stuff related to currencyCode missing.


package com.acme.types;

import java.io.Serializable;

public class Price implements Serializable {

    static final long serialVersionUID = -5418678247307617965L;

    double price = 0;
    String currencyCode = "USD";

    public Price(double pr) {
    price = pr;
    }

    public Price (double pr, String cc) {
    price = pr;
    currencyCode = cc;
    }


    public static double getPrice(Price p) {
    return p.price;
    }

    public static String  getCurrencyCode(Price p) {
    return p.currencyCode;
    }

    public static Price newPrice(double pr) {
    return new Price(pr);
    }


    public String toString() {
    return "My price is " +price + "My Currency code is " + currencyCode;

    }
}
--------
connect 'jdbc:derby:wombat;create=true';
CREATE TYPE price
EXTERNAL NAME 'com.acme.types.Price'
LANGUAGE JAVA;

CREATE FUNCTION newprice(pr double)  RETURNS Price  PARAMETER STYLE 
JAVA NO SQL LANGUAGE JAVA  EXTERNAL NAME 'com.acme.types.Price.newPrice';

CREATE FUNCTION getPrice(pr Price) RETURNS DOUBLE PARAMETER STYLE JAVA 
NO SQL LANGUAGE JAVA EXTERNAL NAME 'com.acme.types.Price.getPrice';


create table items (name LONG VARCHAR, pr Price);

insert into items values('stuffed bear', newprice(2.0));

-- change type to add currencyCode

CREATE FUNCTION getCurrencyCode(pr Price) RETURNS CHAR(3) PARAMETER 
STYLE JAVA NO SQL LANGUAGE JAVA EXTERNAL NAME 
'com.acme.types.Price.getCurrencyCode';


select getCurrencyCode(pr) from items;