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## Nested Attributes

Introduction
Application types
Compound types

## Introduction

In some cases it is desirable to map a plain sequence of fields in a database record to more complicated structure of attributes in a Java object, where the target attributes are contained (nested) in other attributes. In brief, you can specify a path to the target attribute as a name of the field in a configuration file, and Castor is able to handle such nested attributes. For example:

          <field name="address.country.code"...>
            <sql name="person_country"/>
          </field>

## Application types

The first case is an attribute of an application type that is a container for some value of a Java type supported by Castor. Usually the application type also has some business methods. Examples are: class Balance that contains a BigDecimal value and has some accounting-specific methods; class CountryCode that contains a String value and has methods validate(), getDisplayName(), etc.; class Signature that contains a byte[] value and has some security-specific methods. In order to use such type with Castor you should provide a pair of methods to get/set the value of the Castor-supported type, e.g. getBigDecimal/setBigDecimal, getCode/setCode, getBytes/setBytes.

Assume that you have the class Address

            public class Address {
                private CountryCode _country;
                private String      _city;
                private String      _street;

                public CountryCode getCountry() {
                    return _country;
                }

                public void setCountry(CountryCode country) {
                    _country = country;
                }
                ...
            }

where the class CountryCode is like this

            public class CountryCode {
                private String _code;
                private static String[] _allCodes;
                private static String[] _allDisplayNames;

                public String getCode() {
                    return _code;
                }

                public void setCode(String code) {
                    _code = code;
                }

                public void getDisplayName() {
                ...
            }

then write in the configuration file:

        <class name="Address"...>
          <field name="country.code"...>
            <sql name="addr_country"/>
          </field>
          ...
        </class>

When reading the object from the database Castor will use

            object.getCountry().setCode(value);

to set the nested attribute value. Moreover, if object.getCountry() is null, Castor will create the intermediate object of the application type:

            country = new CountryCode();
            country.setCode(value);
            object.setCountry(country);

When writing the object to the database Castor will use

            value = object.getCountry().getCode();

to get the value of the correspondent database field.

## Compound types

The second case is an attribute that is a part of a compound attribute, which contains several database fields. For example, database fields person_country, person_city, person_street of the table PERSON correspond to one compound attribute "address" of the class Person:

            public class Person {
                private String  _firstName;
                private String  _lastName;
                private Address _address;

                public Address getAddress() {
                    return _address;
                }

                public void setAddress(Address address) {
                    _address = address;
                }
                ...
            }

where the class Address is the same as in the previous section. Then write in the configuration file:

        <class name="Person"...>
          <field name="address.country.code"...>
            <sql name="person_country"/>
          </field>
          <field name="address.city"...>
            <sql name="person_city"/>
          </field>
          <field name="address.street"...>
            <sql name="person_street"/>
          </field>
          ...
        </class>

Similarly to the previous section, Castor will use a proper sequence of get/set methods to access the nested attributes and will create the intermediate objects when necessary. Don't forget to provide parameterless constructors for the container classes.

<notice> Copyright © 1999-2005 ExoLab Group, Intalio Inc., and Contributors. All rights reserved. </notice>
<notice> Java, EJB, JDBC, JNDI, JTA, Sun, Sun Microsystems are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and in other countries. XML, XML Schema, XSLT and related standards are trademarks or registered trademarks of MIT, INRIA, Keio or others, and a product of the World Wide Web Consortium. All other product names mentioned herein are trademarks of their respective owners. </notice>