Chapter 20. Toolset Guide

Roundtrip engineering with NHibernate is possible using a set of commandline tools maintained as part of the NHibernate project, along with NHibernate support built into various code generation tools (MyGeneration, CodeSmith, ObjectMapper, AndroMDA).

The NHibernate main package comes bundled with the most important tool (it can even be used from "inside" NHibernate on-the-fly):

Other tools directly provided by the NHibernate project are delivered with a separate package, NHibernateContrib. This package includes tools for the following tasks:

Third party tools with NHibernate support are:

These 3rd party tools are not documented in this reference. Please refer to the NHibernate website for up-to-date information.

20.1. Schema Generation

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.

20.1.1. Customizing the schema

Many NHibernate mapping elements define an optional attribute named length. You may set the length of a column with this attribute. (Or, for numeric/decimal data types, the precision.)

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).

Some tags accept an index attribute for specifying the name of an index for that column. A unique-key attribute can be used to group columns in a single unit key constraint. Currently, the specified value of the unique-key attribute is not used to name the constraint, only to group the columns in the mapping file.


<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="Int64" not-null="true" unique="true"/>

Alternatively, these elements also accept a child <column> element. This is particularly useful for multi-column types:

<property name="Foo" type="String">
    <column name="foo" length="64" not-null="true" sql-type="text"/>

<property name="Bar" type="My.CustomTypes.MultiColumnType, My.CustomTypes"/>
    <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"/>

The sql-type attribute allows the user to override the default mapping of NHibernate type to SQL datatype.

The check attribute allows you to specify a check constraint.

<property name="Foo" type="Int32">
    <column name="foo" check="foo > 10"/>

<class name="Foo" table="foos" check="bar < 100.0">
    <property name="Bar" type="Single"/>

Table 20.1. Summary

lengthnumbercolumn length/decimal precision
not-nulltrue|falsespecfies that the column should be non-nullable
uniquetrue|falsespecifies that the column should have a unique constraint
indexindex_namespecifies the name of a (multi-column) index
unique-keyunique_key_namespecifies the name of a multi-column unique constraint
foreign-keyforeign_key_name specifies the name of the foreign key constraint generated for an association, use it on <one-to-one>, <many-to-one>, <key>, and <many-to-many> mapping elements. Note that inverse="true" sides will not be considered by SchemaExport.
sql-typecolumn_type overrides the default column type (attribute of <column> element only)
checkSQL expression create an SQL check constraint on either column or table

20.1.2. Running the tool

The SchemaExport tool writes a DDL script to standard out and/or executes the DDL statements.

You may embed SchemaExport in your application:

Configuration cfg = ....;
new SchemaExport(cfg).Create(false, true);

20.1.3. Properties

Database properties may be specified

  • as system properties with -D<property>

  • in

  • in a named properties file with --properties

The needed properties are:

Table 20.2. SchemaExport Connection Properties

Property NameDescription
hibernate.connection.driver_classjdbc driver class
hibernate.connection.urljdbc url
hibernate.connection.usernamedatabase user
hibernate.connection.passworduser password

20.1.4. Using Ant

You can call SchemaExport from your Ant build script:

<target name="schemaexport">
    <taskdef name="schemaexport"
        <fileset dir="src">
            <include name="**/*.hbm.xml"/>

If you don't specify properties or a config file, the SchemaExportTask will try to use normal Ant project properties instead. In other words, if you don't want or need an external configuration or properties file, you may put hibernate.* configuration properties in your build.xml or

20.2. Code Generation

The NHibernate code generator may be used to generate skeletal C# implementation classes from a NHibernate mapping file. This tool is included in the NHibernate Contrib package (a saparate download in

hbm2net parses the mapping files and generates fully working C# source files from these. Thus with hbm2net one could "just" provide the .hbm files, and then don't worry about hand-writing/coding the C# files.

hbm2net options mapping_files

Table 20.3. Code Generator Command Line Options

-output:output_dirroot directory for generated code
-config:config_fileoptional file for configuring hbm2net

A more detailed guide of hbm2net is available in