Creating class components

There are cases where a set of properties are used repeatedly. These properties may even have their own business logic, but they do not represent an entity in your application. They are value objects. In this recipe, we will tell you how to separate these properties and business logic into a component class without creating a separate entity.

Getting ready

Complete the Getting ready instructions at the beginning of this chapter.

How to do it…

  1. Add a folder named Components to the MappingRecipes project.
  2. In the folder, add an Address class with the following properties:
    public virtual Guid Id { get; protected set; }
public virtual string Lines { get; set; }
public virtual string City { get; set; }
public virtual string State { get; set; }
public virtual string ZipCode { get; set; }
  3. Add a Customer class with the following properties:
    public virtual string Name { get; set; }
public virtual Address BillingAddress { get; set; }
public virtual Address ShippingAddress { get; set; }
  4. Add the following embedded mapping document:
    <?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
    assembly="MappingRecipes"
    namespace=" MappingRecipes.Components">
  <class name="Customer">
    <id name="Id">
      <generator class="guid.comb" />
    </id>
    <property name="Name" not-null="true" />
    <component name="BillingAddress" class="Address">
      <property name="Lines" not-null="true" 
                column="BillingLines" />
      <property name="City" not-null="true" 
                column="BillingCity" />
      <property name="State" not-null="true" 
                column="BillingState" />
      <property name ="ZipCode" not-null="true" 
                column="BillingZipCode" />
    </component>
    <component name="ShippingAddress" class="Address">
      <property name="Lines" not-null="true" 
                column="ShippingLines" />
      <property name="City" not-null="true" 
                column="ShippingCity" />
      <property name="State" not-null="true" 
                column="ShippingState" />
      <property name ="ZipCode" not-null="true" 
                column="ShippingZipCode" />
    </component>
  </class>
</hibernate-mapping>
  5. Add the following Recipe class:
    using System;
using NH4CookbookHelpers;
using NHibernate;

namespace MappingRecipes.Components
{
  public class Recipe : HbmMappingRecipe
  {
    protected override void AddInitialData(ISession session)
    {
      session.Save(new Customer
      {
        Name = "Max Weinberg",
        BillingAddress = new Address
        {
          Lines = "E Street 1",
          City = "Belmar",
          State = "New Jersey",
          ZipCode = "123"
        },
        ShippingAddress = new Address
        {
          Lines = "Home street",
          City = "Newark",
          State = "New Jersey",
          ZipCode = "123"
        }
      });
    }

    public override void RunQueries(ISession session)
    {
      var customer = session.QueryOver<Customer>()
        .SingleOrDefault();
      Console.WriteLine(
"Customer {0} has a billing address in {1}",
        customer.Name, customer.BillingAddress.City);
    }
  }
}
  6. Run the MappingRecipes application and start the Components recipe.
  7. Investigate the query log and the created tables.

How it works…

In this recipe, we can use the Address component class throughout our model without the overhead of maintaining a separate entity. We have used it in our Customer class for both billing and shipping address.

Our model looks like this:

How it works…

We get all the reuse benefits without the database work. The Address fields are included in every query for Customer and are automatically loaded.

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