I'm a little confused about what goes on behind the scenes in NHibernate when I add a new property to a class.
When I add a property 'Price' to an 'Item' class, my application throws an exception when retrieving Item objects because this new property isn't in the database:
[SqlException (0x80131904): Invalid column name 'Price'.]
Am I supposed to manually add a column to my DB table everytime I declare a new property in a class?
The short answer is: yes, you are.
The class that you're asking nHibernate to map to a table in the database must only have properties that exist as columns in that table. If you want a new property in that class then you need to add a column in the table.
On the other hand, if you want a "Price" property for the Item that's not persisted in the database, then you would have a different class in the application, not under the control of nHibernate, which contains an object of class "Item", with its own "Price" property.
In general, we can use configuration setting for updating our DB schema whenever ISessionFactory is created:
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory>
<property name="hbm2ddl.auto">Update</property>
Check Table 3.2. NHibernate Configuration Properties
We can do it even in our own code:
How to update database table schemas with NHibernate schema generation?
(snippet from Q & A above)
_cfg = new Configuration();
_cfg.Configure();
_cfg.AddAssembly(Assembly.LoadFrom("DataLayer.dll"));
var update = new SchemaUpdate(_cfg);
update.Execute(true, false);
Summary, we can set our Factory to update schema, whenever such Factory is created. It could be used in DEV, but I would say, in DEV only...
