Updating the database

It's usually required to update your database if mappings for your application have changed. In this recipe, we'll generate a SQL script to update your database objects.

Getting ready

Complete the Configuring NHibernate with App.config or Web.config recipe at the beginning of this chapter.

Note

This recipe works for any RDBMS supported by NHibernate. To use a different system, adjust your connection string and dialect accordingly.

How to do it...

1. Open Program.cs.
2. Add these using statements to the beginning of the file:

   using Eg.Core;
   using NHibernate.Mapping.ByCode; 
   using NHibernate.Tool.hbm2ddl;

3. Modify the Main method to look similar to this:

   var nhConfig = new Configuration().Configure();
   var mapper = new ConventionModelMapper();
   nhConfig.AddMapping(mapper.CompileMappingFor(new[] { typeof(TestClass) }));
   var update = new SchemaUpdate(nhConfig);
   update.Execute(false, true);
   Console.WriteLine("The tables have been updated");
   Console.ReadKey();

4. Build and run your application. Inspect the table(s) in the database.
5. Modify TestClass to include an additional property:

   public virtual string Description { get; set; }

6. Build and run the application again. The TestClass table should now have a new column corresponding to the Description property.

How it works...

Using the mapping metadata from the configuration object and the current dialect, hbm2ddl analyzes the existing structure of your database and generates a script to fulfill the differences. The SchemaUpdate only adds missing objects, and does not try to remove anything.

See also

• Configuring NHibernate with App.config
• Configuring NHibernate with hibernate.cfg.xml
• Configuring NHibernate with code
• Configuring NHibernate with Fluent NHibernate
• Generating the database
• Scripting the database