Date: 2004-07-02T03:51:51
Editor: RaphaelMankin <[EMAIL PROTECTED]>
Wiki: DB Torque Wiki
Page: HarderTorqueFaq
URL: http://wiki.apache.org/db-torque/HarderTorqueFaq
Serialising OM objects with XMLEncoder/XMLDecoder
Change Log:
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@@ -37,6 +37,131 @@
---
Yes, you can have a multi-column primary-key, BUT it does not work, if you need one
column of this PK as autoincrement. And this is my problem. The Torque engine looks up
the new key from the sequence and writes it into the System.out/Log-File, but it does
not put it into the PK-field, where I need the value.
-Would be nice, if someone had a solution for this. I found the same problem in
another forum, but there was also no answer to this question.
+Would be nice, if someone had a solution for this. I found the same problem in
another forum, but there was also no answer to this question.
SyncMaster
+
+
+== Using XMLEncoder/XMLDecoder with Torque ==
+
+java.beans.{XMLEncoder,XMLDecoder} is a useful and fairly simple way of transferring
Torque objects to non-Java clients. The encoder uses introspection and will correctly
handle any network of objects that conform to the Java beans conventions.
Unfortunately, Torque's OM classes do not quite conform.
+
+1. If you declare a field as DATE or TIMESTAMP the OM field will be of class
java.util.Date but when you retrieve the object from the database the returned field
will be of type java.sql.Date or java.sql.Timestamp. Since none of these classes is a
valid Java bean the encoder's introspection fails, though it does have special rules
for dealing with java.util.Date.
+
+2. When you have a foreign key Torque generates get and set methods for both the key
and the object referrred to. The introspector does not realise that these are linked
fields and so fetches the underlying object for each foreign key.
+
+The solutions are
+
+1. If you have a field declaration of the form
+
+{{{ <field name="entrydate"
+ type="DATE"
+ />
+}}}
+
+you have to over-ride the getEntrydate() method in the OM class with
+
+{{{
+ public java.util.Date getEntrydate()
+ {
+ java.util.Date d = super.getEntrydate();
+ return (d instance of java.util.Date) ? d :
+ new java.util.Date(d.getTime());
+ }
+}}}
+
+2. To prevent the fetching of underlying objects referred to by foreign keys create a
BeanInfo class for each OM class that has foreign keys.
+
+Suppose that you have the following table declaration, which contains a foreign key.
+
+{{{
+ <table name="MODELEVENT"
+ >
+ <column
+ name="MODELEVENTID"
+ type="INTEGER"
+ required="true"
+ primaryKey="true"
+ autoIncrement="true"
+ />
+ <column
+ name="MODELVERSIONID"
+ type="INTEGER"
+ required="true"
+ />
+ <column
+ name="EVENT"
+ type="VARCHAR"
+ size="50"
+ required="true"
+ />
+ <column
+ name="COMMENTS"
+ type="VARCHAR"
+ size="256"
+ required="false"
+ />
+ <column
+ name="ENTRYDATE"
+ type="TIMESTAMP"
+ required="true"
+ />
+ <column
+ name="PERSON"
+ type="VARCHAR"
+ size="50"
+ required="true"
+ />
+ <foreign-key foreignTable="MODELVERSION">
+ <reference local="MODELVERSIONID" foreign="MODELVERSIONID"/>
+ </foreign-key>
+ </table>
+}}}
+
+You then need to have this BeanInfo class
+
+{{{
+
+package com.gsk.pmf;
+
+import java.beans.IntrospectionException;
+import java.beans.PropertyDescriptor;
+import java.beans.SimpleBeanInfo;
+
+/**
+ * @version $Id;$
+ */
+public class ModeleventBeanInfo extends SimpleBeanInfo {
+ Class meClass = Modelevent.class;
+ /**
+ *
+ */
+ public ModeleventBeanInfo() {
+ super();
+ }
+ public PropertyDescriptor[] getPropertyDescriptors()
+ {
+ try {
+ PropertyDescriptor modelversionid = new
PropertyDescriptor("modelversionid", meClass);
+ PropertyDescriptor modeleventid = new
PropertyDescriptor("modeleventid", meClass);
+ PropertyDescriptor comments = new
PropertyDescriptor("comments", meClass);
+ PropertyDescriptor entrydate = new
PropertyDescriptor("entrydate", meClass);
+ PropertyDescriptor person = new PropertyDescriptor("person",
meClass);
+ PropertyDescriptor event = new PropertyDescriptor("event",
meClass);
+ PropertyDescriptor[] rv = {
+ comments, entrydate, person, modeleventid,
+ event, modelversionid
+ };
+ return rv;
+ } catch (IntrospectionException e) {
+ System.err.println("IntrospectionException"+e.getMessage());
+ e.printStackTrace();
+ }
+ return null;
+ }
+}
+
+
+}}}
+
+This BeanInfo includes the ''modelversionid'' but excludes the ''modelversion'' that
it refers to. The encoder will therefore include the ID field but omit the target
object. It will also omit all the housekeeping fields such as ''new'' and ''modified''.
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