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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"/>
Plusieurs éléments de mapping acceptent aussi un élément fils <column>. Ceci est utile pour les type multi-colonnes:
<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>L'attribut sql-type laisse l'utilisateur surcharger le mapping par défaut du type Hibernate vers un type SQL.
<property name="balance" type="float">
<column name="balance" sql-type="decimal(13,3)"/>
</property>L'attribut check permet de spécifier une contrainte de vérification.
<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.
Tableau 20.1. Summary
| Attribut | Valeur | Interprétation |
|---|---|---|
length | numérique | taille d'une colonne |
precision | numérique | précision décimale de la colonne |
scale | numérique | scale décimale de la colonne |
not-null | true|false | specifies that the column should be non-nullable |
unique | true|false | spécifie que la colonne doit avoir une contrainte d'unicité |
index | index_name | spécifie le nom d'un index (multi-colonnes) |
unique-key | unique_key_name | spécifie le nom d'une contrainte d'unicité multi-colonnes |
foreign-key | foreign_key_name | 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 column_type | overrides the default column type (attribute of <column> element only) |
default | SQL expression | spécifie une valeur par défaut pour la colonne |
check | SQL expression | crée une contrainte de vérification sur la table ou la colonne |
L'élément <comment> vous permet de spécifier un commentaire pour le schéma généré.
<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.
L'outil SchemaExport génère un script DDL vers la sortie standard et/ou exécute les ordres DDL.
The following table displays the SchemaExport command line options
java -cp hibernate_classpaths org.hibernate.tool.hbm2ddl.SchemaExport options mapping_files
Tableau 20.2. SchemaExport Options de la ligne de commande
| Option | Description |
|---|---|
--quiet | do not output the script to stdout |
--drop | supprime seuleument les tables |
--create | ne créé que les tables |
--text | do not export to the database |
--output=my_schema.ddl | écrit le script ddl vers un fichier |
--naming=eg.MyNamingStrategy | select a NamingStrategy |
--config=hibernate.cfg.xml | lit la configuration Hibernate à partir d'un fichier XML |
--properties=hibernate.properties | read database properties from a file |
--format | formatte proprement le SQL généré dans le script |
--delimiter=x | paramètre un délimiteur de fin de ligne pour le script |
You can even embed SchemaExport in your application:
Configuration cfg = ....; new SchemaExport(cfg).create(false, true);
Database properties can be specified:
comme propriétés système avec -D<property>
dans hibernate.properties
dans un fichier de propriétés déclaré avec --properties
Les propriétés nécessaires sont :
Tableau 20.3. SchemaExport Connection Properties
| Nom de la propriété | Description |
|---|---|
hibernate.connection.driver_class | classe du driver JDBC |
hibernate.connection.url | URL JDBC |
hibernate.connection.username | utilisateur de la base de données |
hibernate.connection.password | mot de passe de l'utilisateur |
hibernate.dialect | dialecte |
Vous pouvez appeler SchemaExport depuis votre script de construction Ant :
<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
Tableau 20.4. SchemaUpdate Options de ligne de commande
| Option | Description |
|---|---|
--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);
Vous pouvez appeler SchemaUpdate depuis le script Ant :
<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
Tableau 20.5. SchemaValidator Options de ligne de commande
| Option | Description |
|---|---|
--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();
Vous pouvez appeler SchemaValidator depuis le script Ant:
<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>Copyright © 2004 Red Hat Middleware, LLC.