hibernate-orm/reference/en/modules/toolset_guide.xml

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<chapter id="toolsetguide">
<title>Toolset Guide</title>
<para>
Roundtrip engineering with Hibernate is possible using a set of commandline tools
maintained as part of the Hibernate project, along with Hibernate support built into
XDoclet, Middlegen and AndroMDA.
</para>
<para>
The Hibernate main package comes bundled with the most important tool (it can even
be used from "inside" Hibernate on-the-fly):
</para>
<itemizedlist>
<listitem><para>
DDL schema generation from a mapping file
(aka <literal>SchemaExport</literal>, <literal>hbm2ddl</literal>)
</para></listitem>
</itemizedlist>
<para>
Other tools directly provided by the Hibernate project are delivered with a separate
package, <emphasis>Hibernate Extensions</emphasis>. This package includes tools for
the following tasks:
</para>
<itemizedlist>
<listitem><para>
Java source generation from a mapping file (aka <literal>CodeGenerator</literal>,
<literal>hbm2java</literal>)
</para></listitem>
<listitem><para>
mapping file generation from compiled Java classes or from
Java source with XDoclet markup (aka <literal>MapGenerator</literal>,
<literal>class2hbm</literal>)
</para></listitem>
</itemizedlist>
<para>
There's actually another utitily living in Hibernate Extensions: <literal>ddl2hbm</literal>.
It is considered deprecated and will no longer be maintained, Middlegen does a better job
for the same task.
</para>
<para>
Third party tools with Hibernate support are:
</para>
<itemizedlist>
<listitem><para>
Middlegen (mapping file generation from an existing database schema)
</para></listitem>
<listitem><para>
AndroMDA (MDA (Model-Driven Architecture) approach generating code for
persistent classes from UML diagrams and their XML/XMI representation)
</para></listitem>
</itemizedlist>
<para>
These 3rd party tools are not documented in this reference. Please refer to the Hibernate
website for up-to-date information (a snapshot of the site is included in the Hibernate
main package).
</para>
<sect1 id="toolsetguide-s1">
<title>Schema Generation</title>
<para>
DDL may be generated from your mapping files by a command line utility. A batch file
is located in the <literal>hibernate-x.x.x/bin</literal> directory of the core
Hibernate package.
</para>
<para>
The generated schema include referential integrity constraints (primary and foreign keys) for entity
and collection tables. Tables and sequences are also created for mapped identifier generators.
</para>
<para>
You <emphasis>must</emphasis> specify a SQL <literal>Dialect</literal> via the
<literal>hibernate.dialect</literal> property when using this tool.
</para>
<sect2 id="toolsetguide-s1-2" revision="1">
<title>Customizing the schema</title>
<para>
Many Hibernate mapping elements define an optional attribute named <literal>length</literal>. You may set
the length of a column with this attribute. (Or, for numeric/decimal data types, the precision.)
</para>
<para>
Some tags also accept a <literal>not-null</literal> attribute (for generating a <literal>NOT NULL</literal>
constraint on table columns) and a <literal>unique</literal> attribute (for generating <literal>UNIQUE</literal>
constraint on table columns).
</para>
<para>
Some tags accept an <literal>index</literal> attribute for specifying the
name of an index for that column. A <literal>unique-key</literal> attribute
can be used to group columns in a single unit key constraint. Currently, the
specified value of the <literal>unique-key</literal> attribute is
<emphasis>not</emphasis> used to name the constraint, only to group the
columns in the mapping file.
</para>
<para>
Examples:
</para>
<programlisting><![CDATA[<property name="foo" type="string" length="64" not-null="true"/>
<many-to-one name="bar" foreign-key="fk_foo_bar" not-null="true"/>
<element column="serial_number" type="long" not-null="true" unique="true"/>]]></programlisting>
<para>
Alternatively, these elements also accept a child <literal>&lt;column&gt;</literal> element. This is
particularly useful for multi-column types:
</para>
<programlisting><![CDATA[<property name="foo" type="string">
<column name="foo" length="64" not-null="true" sql-type="text"/>
</property>
<property name="bar" type="my.customtypes.MultiColumnType"/>
<column name="fee" not-null="true" index="bar_idx"/>
<column name="fi" not-null="true" index="bar_idx"/>
<column name="fo" not-null="true" index="bar_idx"/>
</property>]]></programlisting>
<para>
The <literal>sql-type</literal> attribute allows the user to override the default mapping
of Hibernate type to SQL datatype.
</para>
<para>
The <literal>check</literal> attribute allows you to specify a check constraint.
</para>
<programlisting><![CDATA[<property name="foo" type="integer">
<column name="foo" check="foo > 10"/>
</property>
<class name="Foo" table="foos" check="bar < 100.0">
...
<property name="bar" type="float"/>
</class>]]></programlisting>
<table frame="topbot" id="schemattributes-summary" revision="2">
<title>Summary</title>
<tgroup cols="3">
<colspec colwidth="1*"/>
<colspec colwidth="1*"/>
<colspec colwidth="2.5*"/>
<thead>
<row>
<entry>Attribute</entry>
<entry>Values</entry>
<entry>Interpretation</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>length</literal></entry>
<entry>number</entry>
<entry>column length/decimal precision</entry>
</row>
<row>
<entry><literal>not-null</literal></entry>
<entry><literal>true|false</literal></entry>
<entry>specfies that the column should be non-nullable</entry>
</row>
<row>
<entry><literal>unique</literal></entry>
<entry><literal>true|false</literal></entry>
<entry>specifies that the column should have a unique constraint</entry>
</row>
<row>
<entry><literal>index</literal></entry>
<entry><literal>index_name</literal></entry>
<entry>specifies the name of a (multi-column) index</entry>
</row>
<row>
<entry><literal>unique-key</literal></entry>
<entry><literal>unique_key_name</literal></entry>
<entry>specifies the name of a multi-column unique constraint</entry>
</row>
<row>
<entry><literal>foreign-key</literal></entry>
<entry><literal>foreign_key_name</literal></entry>
<entry>
specifies the name of the foreign key constraint generated
for an association, use it on &lt;one-to-one>, &lt;many-to-one>,
&lt;key>, and &lt;many-to-many> mapping elements. Note that
<literal>inverse="true"</literal> sides will not be considered
by <literal>SchemaExport</literal>.
</entry>
</row>
<row>
<entry><literal>sql-type</literal></entry>
<entry><literal>column_type</literal></entry>
<entry>
overrides the default column type (attribute of
<literal>&lt;column&gt;</literal> element only)
</entry>
</row>
<row>
<entry><literal>check</literal></entry>
<entry>SQL expression</entry>
<entry>
create an SQL check constraint on either column or table
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="toolsetguide-s1-3">
<title>Running the tool</title>
<para>
The <literal>SchemaExport</literal> tool writes a DDL script to standard out and/or
executes the DDL statements.
</para>
<para>
<literal>java -cp </literal><emphasis>hibernate_classpaths</emphasis>
<literal>org.hibernate.tool.hbm2ddl.SchemaExport</literal> <emphasis>options mapping_files</emphasis>
</para>
<table frame="topbot">
<title><literal>SchemaExport</literal> Command Line Options</title>
<tgroup cols="2">
<colspec colwidth="1.5*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Option</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>--quiet</literal></entry>
<entry>don't output the script to stdout</entry>
</row>
<row>
<entry><literal>--drop</literal></entry>
<entry>only drop the tables</entry>
</row>
<row>
<entry><literal>--text</literal></entry>
<entry>don't export to the database</entry>
</row>
<row>
<entry><literal>--output=my_schema.ddl</literal></entry>
<entry>output the ddl script to a file</entry>
</row>
<row>
<entry><literal>--config=hibernate.cfg.xml</literal></entry>
<entry>read Hibernate configuration from an XML file</entry>
</row>
<row>
<entry><literal>--properties=hibernate.properties</literal></entry>
<entry>read database properties from a file</entry>
</row>
<row>
<entry><literal>--format</literal></entry>
<entry>format the generated SQL nicely in the script</entry>
</row>
<row>
<entry><literal>--delimiter=x</literal></entry>
<entry>set an end of line delimiter for the script</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
You may even embed <literal>SchemaExport</literal> in your application:
</para>
<programlisting><![CDATA[Configuration cfg = ....;
new SchemaExport(cfg).create(false, true);]]></programlisting>
</sect2>
<sect2 id="toolsetguide-s1-4">
<title>Properties</title>
<para>
Database properties may be specified
</para>
<itemizedlist spacing="compact">
<listitem>
<para>as system properties with <literal>-D</literal><emphasis>&lt;property&gt;</emphasis></para>
</listitem>
<listitem>
<para>in <literal>hibernate.properties</literal></para>
</listitem>
<listitem>
<para>in a named properties file with <literal>--properties</literal></para>
</listitem>
</itemizedlist>
<para>
The needed properties are:
</para>
<table frame="topbot">
<title>SchemaExport Connection Properties</title>
<tgroup cols="2">
<colspec colwidth="1.5*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Property Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>hibernate.connection.driver_class</literal></entry>
<entry>jdbc driver class</entry>
</row>
<row>
<entry><literal>hibernate.connection.url</literal></entry>
<entry>jdbc url</entry>
</row>
<row>
<entry><literal>hibernate.connection.username</literal></entry>
<entry>database user</entry>
</row>
<row>
<entry><literal>hibernate.connection.password</literal></entry>
<entry>user password</entry>
</row>
<row>
<entry><literal>hibernate.dialect</literal></entry>
<entry>dialect</entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="toolsetguide-s1-5">
<title>Using Ant</title>
<para>
You can call <literal>SchemaExport</literal> from your Ant build script:
</para>
<programlisting><![CDATA[<target name="schemaexport">
<taskdef name="schemaexport"
classname="org.hibernate.tool.hbm2ddl.SchemaExportTask"
classpathref="class.path"/>
<schemaexport
properties="hibernate.properties"
quiet="no"
text="no"
drop="no"
delimiter=";"
output="schema-export.sql">
<fileset dir="src">
<include name="**/*.hbm.xml"/>
</fileset>
</schemaexport>
</target>]]></programlisting>
</sect2>
<sect2 id="toolsetguide-s1-6">
<title>Incremental schema updates</title>
<para>
The <literal>SchemaUpdate</literal> tool will update an existing schema with "incremental" changes.
Note that <literal>SchemaUpdate</literal> depends heavily upon the JDBC metadata API, so it will
not work with all JDBC drivers.
</para>
<para>
<literal>java -cp </literal><emphasis>hibernate_classpaths</emphasis>
<literal>org.hibernate.tool.hbm2ddl.SchemaUpdate</literal> <emphasis>options mapping_files</emphasis>
</para>
<table frame="topbot">
<title><literal>SchemaUpdate</literal> Command Line Options</title>
<tgroup cols="2">
<colspec colwidth="1.5*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Option</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>--quiet</literal></entry>
<entry>don't output the script to stdout</entry>
</row>
<row>
<entry><literal>--properties=hibernate.properties</literal></entry>
<entry>read database properties from a file</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
You may embed <literal>SchemaUpdate</literal> in your application:
</para>
<programlisting><![CDATA[Configuration cfg = ....;
new SchemaUpdate(cfg).execute(false);]]></programlisting>
</sect2>
<sect2 id="toolsetguide-s1-7">
<title>Using Ant for incremental schema updates</title>
<para>
You can call <literal>SchemaUpdate</literal> from the Ant script:
</para>
<programlisting><![CDATA[<target name="schemaupdate">
<taskdef name="schemaupdate"
classname="org.hibernate.tool.hbm2ddl.SchemaUpdateTask"
classpathref="class.path"/>
<schemaupdate
properties="hibernate.properties"
quiet="no">
<fileset dir="src">
<include name="**/*.hbm.xml"/>
</fileset>
</schemaupdate>
</target>]]></programlisting>
</sect2>
</sect1>
<sect1 id="toolsetguide-s2">
<title>Code Generation</title>
<para>
The Hibernate code generator may be used to generate skeletal Java implementation classes
from a Hibernate mapping file. This tool is included in the Hibernate Extensions package
(a seperate download).
</para>
<para>
<literal>hbm2java</literal> parses the mapping files and generates fully working Java
source files from these. Thus with <literal>hbm2java</literal> one could "just" provide the
<literal>.hbm</literal> files, and then don't worry about hand-writing/coding the Java files.
</para>
<para>
<literal>java -cp</literal> <emphasis>hibernate_classpaths</emphasis>
<literal>org.hibernate.tool.hbm2java.CodeGenerator</literal> <emphasis> options
mapping_files</emphasis>
</para>
<table frame="topbot">
<title>Code Generator Command Line Options</title>
<tgroup cols="2">
<colspec colwidth="1*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Option</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>--output=</literal><emphasis>output_dir</emphasis></entry>
<entry>root directory for generated code</entry>
</row>
<row>
<entry><literal>--config=</literal><emphasis>config_file</emphasis></entry>
<entry>optional file for configuring hbm2java</entry>
</row>
</tbody>
</tgroup>
</table>
<sect2 id="toolsetguide-s2-1" revision="4">
<title>The config file (optional)</title>
<para>
The config file provides for a way to specify multiple "renderers" for the source code
and to declare <literal>&lt;meta&gt;</literal> attributes that is "global" in scope. See
more about this in the <literal>&lt;meta&gt;</literal> attribute section.
</para>
<programlisting><![CDATA[<codegen>
<meta attribute="implements">codegen.test.IAuditable</meta>
<generate renderer="org.hibernate.tool.hbm2java.BasicRenderer"/>
<generate
package="autofinders.only"
suffix="Finder"
renderer="org.hibernate.tool.hbm2java.FinderRenderer"/>
</codegen>]]></programlisting>
<para>
This config file declares a global meta attribute "implements" and specify two renderers, the
default one (BasicRenderer) and a renderer that generates Finder's (See more in "Basic Finder
generation" below).
</para>
<para>
The second renderer is provided with a package and suffix attribute.
</para>
<para>
The package attribute specifies that the generated source files from this renderer should be
placed here instead of the package scope specified in the <literal>.hbm</literal> files.
</para>
<para>
The suffix attribute specifies the suffix for generated files. E.g. here a file named
<literal>Foo.java</literal> would be <literal>FooFinder.java</literal> instead.
</para>
<para>
It is also possible to send down arbitrary parameters to the renders by adding <literal>&lt;param&gt;</literal> attributes
to the <literal>&lt;generate&gt;</literal> elements.
</para>
<para>
hbm2java currently has support for one such parameter,
namely
<literal>generate-concrete-empty-classes</literal> which
informs the BasicRenderer to only generate empty
concrete classes that extends a base class for all your
classes. The following config.xml example illustrate
this feature
</para>
<programlisting><![CDATA[
<codegen>
<generate prefix="Base" renderer="org.hibernate.tool.hbm2java.BasicRenderer"/>
<generate renderer="org.hibernate.tool.hbm2java.BasicRenderer">
<param name="generate-concrete-empty-classes">true</param>
<param name="baseclass-prefix">Base</param>
</generate>
</codegen>]]></programlisting>
<para>
Notice that this config.xml configure 2 (two)
renderers. One that generates the Base classes, and a
second one that just generates empty concrete classes.
</para>
</sect2>
<sect2 id="toolsetguide-s2-2">
<title>The <literal>meta</literal> attribute</title>
<para>
The <literal>&lt;meta&gt;</literal> tag is a simple way of annotating the <literal>hbm.xml</literal>
with information, so tools have a natural place to store/read information that is not directly related
to the Hibernate core.
</para>
<para>
You can use the <literal>&lt;meta&gt;</literal> tag to tell <literal>hbm2java</literal> to only
generate "protected" setters, have classes always implement a certain set of interfaces or
even have them extend a certain base class and even more.
</para>
<para>
The following example:
</para>
<programlisting><![CDATA[<class name="Person">
<meta attribute="class-description">
Javadoc for the Person class
@author Frodo
</meta>
<meta attribute="implements">IAuditable</meta>
<id name="id" type="long">
<meta attribute="scope-set">protected</meta>
<generator class="increment"/>
</id>
<property name="name" type="string">
<meta attribute="field-description">The name of the person</meta>
</property>
</class>]]></programlisting>
<para>
will produce something like the following (code shortened for better understanding). Notice the
Javadoc comment and the protected set methods:
</para>
<programlisting><![CDATA[// default package
import java.io.Serializable;
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.ToStringBuilder;
/**
* Javadoc for the Person class
* @author Frodo
*
*/
public class Person implements Serializable, IAuditable {
/** identifier field */
public Long id;
/** nullable persistent field */
public String name;
/** full constructor */
public Person(java.lang.String name) {
this.name = name;
}
/** default constructor */
public Person() {
}
public java.lang.Long getId() {
return this.id;
}
protected void setId(java.lang.Long id) {
this.id = id;
}
/**
* The name of the person
*/
public java.lang.String getName() {
return this.name;
}
public void setName(java.lang.String name) {
this.name = name;
}
}]]></programlisting>
<table frame="topbot">
<title>Supported meta tags</title>
<tgroup cols="2">
<colspec colwidth="1.5*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Attribute</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>class-description</literal></entry>
<entry>inserted into the javadoc for classes</entry>
</row>
<row>
<entry><literal>field-description</literal></entry>
<entry>inserted into the javadoc for fields/properties</entry>
</row>
<row>
<entry><literal>interface</literal></entry>
<entry>If true an interface is generated instead of an class.</entry>
</row>
<row>
<entry><literal>implements</literal></entry>
<entry>interface the class should implement</entry>
</row>
<row>
<entry><literal>extends</literal></entry>
<entry>class the class should extend (ignored for subclasses)</entry>
</row>
<row>
<entry><literal>generated-class</literal></entry>
<entry>overrule the name of the actual class generated</entry>
</row>
<row>
<entry><literal>scope-class</literal></entry>
<entry>scope for class </entry>
</row>
<row>
<entry><literal>scope-set</literal></entry>
<entry>scope for setter method</entry>
</row>
<row>
<entry><literal>scope-get</literal></entry>
<entry>scope for getter method</entry>
</row>
<row>
<entry><literal>scope-field</literal></entry>
<entry>scope for actual field</entry>
</row>
<row>
<entry><literal>use-in-tostring</literal></entry>
<entry>include this property in the <literal>toString()</literal></entry>
</row>
<row>
<entry><literal>implement-equals</literal></entry>
<entry>include a <literal>equals()</literal> and <literal>hashCode()</literal> method in this class.</entry>
</row>
<row>
<entry><literal>use-in-equals</literal></entry>
<entry>include this property in the <literal>equals()</literal> and <literal>hashCode()</literal> method.</entry>
</row>
<row>
<entry><literal>bound</literal></entry>
<entry>add propertyChangeListener support for a property</entry>
</row>
<row>
<entry><literal>constrained</literal></entry>
<entry>bound + vetoChangeListener support for a property</entry>
</row>
<row>
<entry><literal>gen-property</literal></entry>
<entry>property will not be generated if false (use with care)</entry>
</row>
<row>
<entry><literal>property-type</literal></entry>
<entry>Overrides the default type of property. Use this with any tag's to specify the concrete type instead of just Object.</entry>
</row>
<row>
<entry><literal>class-code</literal></entry>
<entry>Extra code that will inserted at the end of the class</entry>
</row>
<row>
<entry><literal>extra-import</literal></entry>
<entry>Extra import that will inserted at the end of all other imports</entry>
</row>
<row>
<entry><literal>finder-method</literal></entry>
<entry>see "Basic finder generator" below</entry>
</row>
<row>
<entry><literal>session-method</literal></entry>
<entry>see "Basic finder generator" below</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Attributes declared via the <literal>&lt;meta&gt;</literal> tag are per default
"inherited" inside an <literal>hbm.xml</literal> file.
</para>
<para>
What does that mean? It means that if you e.g want to have all your classes
implement <literal>IAuditable</literal> then you just add an
<literal>&lt;meta attribute="implements"&gt;IAuditable&lt;/meta&gt;</literal> in the top of
the <literal>hbm.xml</literal> file, just after
<literal>&lt;hibernate-mapping&gt;</literal>. Now all classes defined in that
<literal>hbm.xml</literal> file will implement <literal>IAuditable</literal>!
(Except if a class also has an "implements" meta attribute, because local specified
meta tags always overrules/replaces any inherited meta tags).
</para>
<para>
Note: This applies to <emphasis>all</emphasis> <literal>&lt;meta&gt;</literal>-tags.
Thus it can also e.g. be used to specify that all fields should be declare protected,
instead of the default private. This is done by adding <literal>&lt;meta
attribute="scope-field"&gt;protected&lt;/meta&gt;</literal> at e.g. just under the
<literal>&lt;class&gt;</literal> tag and all fields of that class will be protected.
</para>
<para>
To avoid having a <literal>&lt;meta&gt;</literal>-tag inherited then you can simply
specify <literal>inherit="false"</literal> for the attribute, e.g.
<literal>&lt;meta attribute="scope-class" inherit="false"&gt;public abstract&lt;/meta&gt;</literal>
will restrict the "class-scope" to the current class, not the subclasses.
</para>
</sect2>
<sect2 id="toolsetguide-s2-3">
<title>Basic finder generator</title>
<para>
It is now possible to have <literal>hbm2java</literal> generate basic finders for
Hibernate properties. This requires two things in the <literal>hbm.xml</literal>
files.
</para>
<para>
The first is an indication of which fields you want to generate finders for. You indicate
that with a meta block inside a property tag such as:
</para>
<programlisting><![CDATA[<property name="name" column="name" type="string">
<meta attribute="finder-method">findByName</meta>
</property>]]></programlisting>
<para>
The finder method name will be the text enclosed in the meta tags.
</para>
<para>
The second is to create a config file for hbm2java of the format:
</para>
<programlisting><![CDATA[<codegen>
<generate renderer="org.hibernate.tool.hbm2java.BasicRenderer"/>
<generate suffix="Finder" renderer="org.hibernate.tool.hbm2java.FinderRenderer"/>
</codegen>]]></programlisting>
<para>
And then use the param to <literal>hbm2java --config=xxx.xml</literal> where
<literal>xxx.xml</literal> is the config file you just created.
</para>
<para>
An optional parameter is meta tag at the class level of the format:
</para>
<programlisting><![CDATA[<meta attribute="session-method">
com.whatever.SessionTable.getSessionTable().getSession();
</meta>]]></programlisting>
<para>
Which would be the way in which you get sessions if you use the
<emphasis>Thread Local Session</emphasis> pattern (documented in the Design Patterns
area of the Hibernate website).
</para>
</sect2>
<sect2 id="toolsetguide-s2-4">
<title>Velocity based renderer/generator</title>
<para>It is now possible to use velocity as an alternative rendering mechanism.
The follwing config.xml shows how to configure hbm2java to use its velocity renderer.
</para>
<programlisting><![CDATA[
<codegen>
<generate renderer="org.hibernate.tool.hbm2java.VelocityRenderer">
<param name="template">pojo.vm</param>
</generate>
</codegen>]]></programlisting>
<para>
The parameter named <literal>template</literal> is a resource path to the velocity macro file you want to use.
This file must be available via the classpath for hbm2java. Thus remember to add the directory where pojo.vm
is located to your ant task or shell script. (The default location is <literal>./tools/src/velocity</literal>)
</para>
<para>
Be aware that the current <literal>pojo.vm</literal> generates only the most basic parts of the java beans.
It is not as complete and feature rich as the default renderer - primarily a lot of the <literal>meta</literal> tags
are not supported.
</para>
</sect2>
</sect1>
<sect1 id="toolsetguide-s3" revision="1">
<title>Mapping File Generation</title>
<para>
A skeletal mapping file may be generated from compiled persistent classes using
a command line utility called <literal>MapGenerator</literal>. This utility is part of
the Hibernate Extensions package.
</para>
<para>
The Hibernate mapping generator provides a mechanism to produce mappings from
compiled classes. It uses Java reflection to find <emphasis>properties</emphasis>
and uses heuristics to guess an appropriate mapping from the property type.
The generated mapping is intended to be a starting point only. There is no way to produce
a full Hibernate mapping without extra input from the user. However, the tool does
take away some of the repetitive "grunt" work involved in producing a mapping.
</para>
<para>
Classes are added to the mapping one at a time. The tool will reject
classes that it judges are are not <emphasis>Hibernate persistable</emphasis>.
</para>
<para>
To be <emphasis>Hibernate persistable</emphasis> a class
</para>
<itemizedlist spacing="compact">
<listitem>
<para>must not be a primitive type</para>
</listitem>
<listitem>
<para>must not be an array</para>
</listitem>
<listitem>
<para>must not be an interface</para>
</listitem>
<listitem>
<para>must not be a nested class</para>
</listitem>
<listitem>
<para>must have a default (zero argument) constructor.</para>
</listitem>
</itemizedlist>
<para>
Note that interfaces and nested classes actually are persistable by Hibernate, but
this would not usually be intended by the user.
</para>
<para>
<literal>MapGenerator</literal> will climb the superclass chain of all added classes attempting
to add as many Hibernate persistable superclasses as possible to the same database table.
The search stops as soon as a property is found that has a name appearing on a list of
<emphasis>candidate UID names</emphasis>.
</para>
<para>
The default list of candidate UID property names is: <literal>uid</literal>, <literal>UID</literal>,
<literal>id</literal>, <literal>ID</literal>, <literal>key</literal>, <literal>KEY</literal>,
<literal>pk</literal>, <literal>PK</literal>.
</para>
<para>
Properties are discovered when there are two methods in the class, a setter and a getter, where the
type of the setter's single argument is the same as the return type of the zero argument getter,
and the setter returns <literal>void</literal>. Furthermore, the setter's name must start with the
string <literal>set</literal> and either the getter's name starts with <literal>get</literal> or
the getter's name starts with <literal>is</literal> and the type of the property is boolean. In
either case, the remainder of their names must match. This matching portion is the name of
the property, except that the initial character of the property name is made lower case if
the second letter is lower case.
</para>
<para>
The rules for determining the database type of each property are as follows:
</para>
<orderedlist spacing="compact">
<listitem>
<para>
If the Java type is <literal>Hibernate.basic()</literal>, then the property is a
simple column of that type.
</para>
</listitem>
<listitem>
<para>
For <literal>hibernate.type.Type</literal> custom types a simple column is used as well.
</para>
</listitem>
<listitem>
<para>
If the property type is an array, then a Hibernate array is used, and <literal>MapGenerator</literal>
attempts to reflect on the array element type.
</para>
</listitem>
<listitem>
<para>
If the property has type <literal>java.util.List</literal>, <literal>java.util.Map</literal>, or
<literal>java.util.Set</literal>, then the corresponding Hibernate types are used, but
<literal>MapGenerator</literal> cannot further process the insides of these types.
</para>
</listitem>
<listitem>
<para>
If the property's type is any other class, <literal>MapGenerator</literal> defers the decision
on the database representation until all classes have been processed. At this point, if the
class was discovered through the superclass search described above, then the property is
an <literal>many-to-one</literal> association. If the class has any properties, then it is
a <literal>component</literal>. Otherwise it is serializable, or not persistable.
</para>
</listitem>
</orderedlist>
<sect2 id="toolsetguide-s3-1">
<title>Running the tool</title>
<para>
The tool writes XML mappings to standard out and/or to a file.
</para>
<para>
When invoking the tool you must place your compiled classes on the classpath.
</para>
<para>
<literal>java -cp </literal><emphasis>hibernate_and_your_class_classpaths</emphasis>
<literal>org.hibernate.tool.class2hbm.MapGenerator</literal> <emphasis>options and
classnames</emphasis>
</para>
<para>
There are two modes of operation: command line or interactive.
</para>
<para>
The interactive mode is selected by providing the single command line argument
<literal>--interact</literal>. This mode provides a prompt response console. Using it you
can set the UID property name for each class using the <literal>uid=XXX</literal> command
where <literal>XXX</literal> is the UID property name. Other command alternatives are simply
a fully qualified class name, or the command done which emits the XML and terminates.
</para>
<para>
In command line mode the arguments are the options below interspersed with fully qualified
class names of the classes to be processed. Most of the options are meant to be used
multiple times; each use affects subsequently added classes.
</para>
<table frame="topbot">
<title>MapGenerator Command Line Options</title>
<tgroup cols="2">
<colspec colwidth="1*"/>
<colspec colwidth="2*"/>
<thead>
<row>
<entry>Option</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>--quiet</literal></entry>
<entry>don't output the O-R Mapping to stdout</entry>
</row>
<row>
<entry><literal>--setUID=uid</literal></entry>
<entry>set the list of candidate UIDs to the singleton uid</entry>
</row>
<row>
<entry><literal>--addUID=uid</literal></entry>
<entry>add uid to the front of the list of candidate UIDs</entry>
</row>
<row>
<entry><literal>--select=</literal><emphasis>mode</emphasis></entry>
<entry>mode use select mode <emphasis>mode</emphasis>(e.g.,
<emphasis>distinct</emphasis> or <emphasis>all</emphasis>) for subsequently
added classes</entry>
</row>
<row>
<entry><literal>--depth=&lt;small-int&gt;</literal></entry>
<entry>limit the depth of component data recursion for subsequently added classes</entry>
</row>
<row>
<entry><literal>--output=my_mapping.xml</literal></entry>
<entry>output the O-R Mapping to a file</entry>
</row>
<row>
<entry><emphasis>full.class.Name</emphasis></entry>
<entry>add the class to the mapping</entry>
</row>
<row>
<entry><literal>--abstract=</literal><emphasis>full.class.Name</emphasis></entry>
<entry>see below</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The abstract switch directs the map generator tool to ignore specific super classes so
that classes with common inheritance are not mapped to one large table. For instance,
consider these class hierarchies:
</para>
<para>
<literal>Animal-->Mammal-->Human</literal>
</para>
<para>
<literal>Animal-->Mammal-->Marsupial-->Kangaroo</literal>
</para>
<para>
If the <literal>--abstract</literal>switch is <emphasis>not</emphasis> used, all classes will
be mapped as subclasses of <literal>Animal</literal>, resulting in one large table containing
all the properties of all the classes plus a discriminator column to indicate which subclass is
actually stored. If <literal>Mammal</literal> is marked as <literal>abstract</literal>,
<literal>Human</literal> and <literal>Marsupial</literal> will be mapped to
separate <literal>&lt;class&gt;</literal> declarations and stored in separate tables.
<literal>Kangaroo</literal> will still be a subclass of <literal>Marsupial</literal>
unless <literal>Marsupial</literal> is also marked as <literal>abstract</literal>.
</para>
</sect2>
</sect1>
</chapter>