The preceding method creates a session factory
Let's first create a new category object. We can do this by using the following code snippet:
var category = new Category{Name = "Beverages",Description = "Some description"};
Next, we want to save this new category object and we can do so by using the following code:
var id = session.Save(category);
The value that is returned from the save method corresponds to the ID of the newly createdcategory object.
Now, let's create a product. The product has a reference to a category object. Before we can save a product, the corresponding category object must have been persisted to the database. The following code would work:
var category = new Category { Name = "Beverages" };
var product = new Product { Name = "Milk", Category = category };
session.Save(category);
session.Save(product);
The session object can also be used to delete an existing object from the database. The command to do so is as simple as the following code:
session.Delete(category);
Here, the category object we pass as a parameter to the delete method corresponds to the one we want to remove from the database.
Reading from the database
Persisting data into a database is surely important, but we also want to be able to reuse this data and thus must have a means to access it. The NHibernate session object provides us with this possibility. We can use the session object directly to access a single object in the database, which is identified by its primary key by using the following code:
var category = session.Get<Category>(1);
NHibernate will query the database for a category record in the category table having an ID of 1. NHibernate will then take this data and create a category object from it. We also say, "NHibernate rehydrates an object".
If we want to read not only a single object, but a list of objects from the database, we can use the LINQ to NHibernate provider to do so. The following statement will read all records from the category table and generate a list of the category objects out of it:
var categories = session.Query<Category>();
We can even go a step further and, for example, query a list of all discontinued products sorted by their name with the following statement:
var products = session.Query<Product>()
.Where(p =>p.Discontinued)
.OrderBy(p =>p.Name);