Nhi Musthaveatleastone Check

post_id: 98 / post_date: 2012-02-01

[tab:PS]
NHibernate doesnt have a way to check whether a List has atleast one item.
This kind of validation is important and if it fails, atleast the save should catch it.
This can be done with a neat Mapper extension and an on save listener.

//Register with the NH Configuration
configuration.SetListener(ListenerType.SaveUpdate, new HasAtleastOne.Listener());

//Use in the classMap
HasMany(x => x.Links).KeyColumn("Project_id").MustHaveAtleastOne();

//Test the code
var l = new HasAtleastOne.Listener();
var e = new Project();
l.TestSave(e);

[tab:code]
[iframe src="http://cselian.com/d/code/serve.php?file=./snippets/HasAtleastOne.cs"]