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Roundtrip engineering with Hibernate is possible using a set of Eclipse plugins, commandline tools, and Ant tasks.
Hibernate Tools currently include plugins for the Eclipse IDE as well as Ant tasks for reverse engineering of existing databases:
Mapping Editor: an editor for Hibernate XML mapping files that supports auto-completion and syntax highlighting. It also supports semantic auto-completion for class names and property/field names, making it more versatile than a normal XML editor.
Console: the console is a new view in Eclipse. In addition to a tree overview of your console configurations, you are also provided with an interactive view of your persistent classes and their relationships. The console allows you to execute HQL queries against your database and browse the result directly in Eclipse.
Development Wizards: several wizards are provided with the Hibernate Eclipse tools. You can use a wizard to quickly generate Hibernate configuration (cfg.xml) files, or to reverse engineer an existing database schema into POJO source files and Hibernate mapping files. The reverse engineering wizard supports customizable templates.
Please refer to the Hibernate Tools package documentation for more information.
However, the Hibernate main package comes bundled with an integrated tool : SchemaExport aka hbm2ddl.It can even be used from "inside" Hibernate.
DDL can be generated from your mapping files by a Hibernate utility. The generated schema includes referential integrity constraints, primary and foreign keys, for entity and collection tables. Tables and sequences are also created for mapped identifier generators.
You must specify a SQL Dialect via the hibernate.dialect property when using this tool, as DDL is highly vendor-specific.
First, you must customize your mapping files to improve the generated schema. The next section covers schema customization.
Many Hibernate mapping elements define optional attributes named length, precision and scale. You can set the length, precision and scale of a column with this attribute.
<property name="zip" length="5"/>
<property name="balance" precision="12" scale="2"/>
Some tags also accept a not-null attribute for generating a NOT NULL constraint on table columns, and a unique attribute for generating UNIQUE constraint on table columns.
<many-to-one name="bar" column="barId" not-null="true"/>
<element column="serialNumber" type="long" not-null="true" unique="true"/>
A unique-key attribute can be used to group columns in a single, unique key constraint. Currently, the specified value of the unique-key attribute is not used to name the constraint in the generated DDL. It is only used to group the columns in the mapping file.
<many-to-one name="org" column="orgId" unique-key="OrgEmployeeId"/> <property name="employeeId" unique-key="OrgEmployee"/>
An index attribute specifies the name of an index that will be created using the mapped column or columns. Multiple columns can be grouped into the same index by simply specifying the same index name.
<property name="lastName" index="CustName"/> <property name="firstName" index="CustName"/>
A foreign-key attribute can be used to override the name of any generated foreign key constraint.
<many-to-one name="bar" column="barId" foreign-key="FKFooBar"/>
多くのマッピング要素は、子 <column> 要素を記述できます。これは複数カラム型のマッピングには特に有用です。
<property name="name" type="my.customtypes.Name"/>
<column name="last" not-null="true" index="bar_idx" length="30"/>
<column name="first" not-null="true" index="bar_idx" length="20"/>
<column name="initial"/>
</property>The default attribute allows you to specify a default value for a column.You should assign the same value to the mapped property before saving a new instance of the mapped class.
<property name="credits" type="integer" insert="false">
<column name="credits" default="10"/>
</property><version name="version" type="integer" insert="false">
<column name="version" default="0"/>
</property>sql-type 属性で、デフォルトのHibernate型からSQLのデータ型へのマッピングをオーバーライドできます。
<property name="balance" type="float">
<column name="balance" sql-type="decimal(13,3)"/>
</property>check 属性でチェック制約を指定することができます。
<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>The following table summarizes these optional attributes.
表 20.1. まとめ
| 属性 | 値 | 説明 |
|---|---|---|
length | 数値 | カラムの長さ |
precision | 数値 | カラムのDECIMAL型の精度（precision） |
scale | 数値 | カラムのDECIMAL型のスケール（scale） |
not-null | true|false | specifies that the column should be non-nullable |
unique | true|false | カラムがユニーク制約を持つことを指定します |
index | インデックス名 | (複数カラムの)インデックスの名前を指定します |
unique-key | ユニークキー名 | 複数カラムのユニーク制約の名前を指定します |
foreign-key | 外部キー名 | specifies the name of the foreign key constraint generated for an association, for a <one-to-one>, <many-to-one>, <key>, or <many-to-many> mapping element. Note that inverse="true" sides will not be considered by SchemaExport. |
sql-type | SQLのカラム型 | overrides the default column type (attribute of <column> element only) |
default | SQL式 | カラムのデフォルト値を指定します |
check | SQL式 | カラムかテーブルにSQLのチェック制約を作成します |
<comment> 要素で生成するスキーマにコメントを指定することができます。
<class name="Customer" table="CurCust">
<comment>Current customers only</comment>
...
</class><property name="balance">
<column name="bal">
<comment>Balance in USD</comment>
</column>
</property>This results in a comment on table or comment on column statement in the generated DDL where supported.
SchemaExport は標準出力に対してDDLスクリプトを書き出し、DDL文を実行したりもします。
The following table displays the SchemaExport command line options
java -cp hibernate_classpaths org.hibernate.tool.hbm2ddl.SchemaExport options mapping_files
表 20.2. SchemaExport Command Line Options SchemaExport のコマンドラインオプション
| オプション | 説明 |
|---|---|
--quiet | do not output the script to stdout |
--drop | テーブルの削除だけを行います |
--create | テーブルの生成のみを行います。 |
--text | do not export to the database |
--output=my_schema.ddl | DDLスクリプトをファイルに出力します |
--naming=eg.MyNamingStrategy | select a NamingStrategy |
--config=hibernate.cfg.xml | XMLファイルからHibernateの定義情報を読み込みます |
--properties=hibernate.properties | read database properties from a file |
--format | スクリプト内に生成するSQLを読みやすいようにフォーマットします |
--delimiter=x | スクリプトの行区切り文字を設定します |
You can even embed SchemaExport in your application:
Configuration cfg = ....; new SchemaExport(cfg).create(false, true);
Database properties can be specified:
-D<property> を使って、システムプロパティとして
hibernate.properties ファイル内で
--properties を使って指定したプロパティファイル内で
必要なプロパティは以下のものです：
表 20.3. SchemaExportコネクションプロパティ
| プロパティ名 | 説明 |
|---|---|
hibernate.connection.driver_class | jdbcのドライバークラス |
hibernate.connection.url | jdbcのurl |
hibernate.connection.username | データベースのユーザ |
hibernate.connection.password | ユーザパスワード |
hibernate.dialect | データベース方言 |
Antのビルドスクリプトから SchemaExport を呼び出すことができます。:
<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>The SchemaUpdate tool will update an existing schema with "incremental" changes. The SchemaUpdate depends upon the JDBC metadata API and, as such, will not work with all JDBC drivers.
java -cp hibernate_classpaths org.hibernate.tool.hbm2ddl.SchemaUpdate options mapping_files
表 20.4. SchemaUpdate のコマンドライン･オプション
| オプション | 説明 |
|---|---|
--quiet | do not output the script to stdout |
--text | do not export the script to the database |
--naming=eg.MyNamingStrategy | select a NamingStrategy |
--properties=hibernate.properties | read database properties from a file |
--config=hibernate.cfg.xml | specify a .cfg.xml file |
You can embed SchemaUpdate in your application:
Configuration cfg = ....; new SchemaUpdate(cfg).execute(false);
Antスクリプトから SchemaUpdate を呼び出すことができます：
<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>The SchemaValidator tool will validate that the existing database schema "matches" your mapping documents. The SchemaValidator depends heavily upon the JDBC metadata API and, as such, will not work with all JDBC drivers. This tool is extremely useful for testing.
java -cp hibernate_classpaths org.hibernate.tool.hbm2ddl.SchemaValidator options mapping_files
表 20.5. SchemaValidator のコマンドライン・オプション
| オプション | 説明 |
|---|---|
--naming=eg.MyNamingStrategy | select a NamingStrategy |
--properties=hibernate.properties | read database properties from a file |
--config=hibernate.cfg.xml | specify a .cfg.xml file |
You can embed SchemaValidator in your application:
Configuration cfg = ....; new SchemaValidator(cfg).validate();
Antスクリプトから SchemaValidator を呼び出せます:
<target name="schemavalidate">
<taskdef name="schemavalidator"
classname="org.hibernate.tool.hbm2ddl.SchemaValidatorTask"
classpathref="class.path"/>
<schemavalidator
properties="hibernate.properties">
<fileset dir="src">
<include name="**/*.hbm.xml"/>
</fileset>
</schemavalidator>
</target>製作著作 © 2004 Red Hat Middleware, LLC.