学步园

在NHibernate做字段映射时,一般会把数据库中的数字类型映射为.Net中的值类型,例如SqlServer中的int映射为Int32类型,如果不给此字段赋值，系统将给出默认值，Int32将给出0，而存到数据库中的值也就成了0。虽然我们可以在读取数据时作出处理，发现这样的值当成不合法的数据不予显示。但这样做似乎有些别扭，而且让数据库白白的存些没有用的数据，实在有些浪费。

NHibernateContrib中的Nullables和Nullables.NHibernate给我们提供了解决方法。

Nullables: A library of Nullable version of the ValueTypes in net-1.1. It is meant to serve as a bridge until .net-2.0 comes out with their own Nullables.

Nullables.NHibernate: A library of NHibernate Types for the Nullables.

做个最简单的实验，有个表叫studnets,有三个字段
 [id] [int] IDENTITY (1, 1) NOT NULL ,             //PRIMARY KEY
 [name] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL ,
 [age] [int] NULL

普通方式

using System;

namespace NHTest
{
    /// <summary>
    /// Student
    /// </summary>
    public class Student
    {
        public Student()
        {
        }

        private int m_ID;
        private string m_Name=null;
        private int m_Age;

        public int ID
        {
            get
            {
                return m_ID;
            }
        }

        public string Name
        {
            get
            {
                return m_Name;
            }
            set
            {
                m_Name=value;
            }
        }

        public int Age
        {
            get
            {
                return m_Age;
            }
            set
            {
                m_Age=value;
            }
        }
    }
}

<?xml version="1.0" encoding="utf-8" ?> 
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
    <class name="NHTest.Student,NHTest" table="students">
        <id name="m_ID" column="id"  type="Int32" unsaved-value="0" access="field">
            <generator class="native"></generator>
        </id>
        <property name="Name" column="name" type="String"></property>
        
        <property name="Age" column="age" type="Int32"></property>
        
    </class>
</hibernate-mapping>

使用Nullables

using System;
using Nullables.NHibernate;
using Nullables;

namespace NHTest
{
    /// <summary>
    /// 允许age为Nullables的Student
    /// </summary>
    public class StudentN
    {
        public StudentN()
        {
        }

        private int m_ID=0;
        private string m_Name=null;
        private NullableInt32 m_Age=null;

        public int ID
        {
            get
            {
                return m_ID;
            }
        }

        public string Name
        {
            get
            {
                return m_Name;
            }
            set
            {
                m_Name=value;
            }
        }

        public NullableInt32 Age
        {
            get
            {
                return m_Age;
            }
            set
            {
                m_Age=value;
            }
        }
        
    }
}

<?xml version="1.0" encoding="utf-8" ?> 
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
    <class name="NHTest.StudentN,NHTest" table="students">
        <id name="m_ID" column="id"  type="Int32" unsaved-value="0" access="field">
            <generator class="native"></generator>
        </id>
        <property name="Name" column="name" type="String"></property>
        
        <property name="Age" column="age" type="Nullables.NHibernate.NullableInt32Type,Nullables.NHibernate"></property>
        
    </class>
</hibernate-mapping>

我的测试代码如下

using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections;

using NUnit.Framework;
using NHibernate;
using NHibernate.Cfg;

namespace NHTest
{
    [TestFixture]
    public class TestCase
    {
        [SetUp]
        public void SetUp()
        {
    
        }
    
        [TearDown]
        public void TearDown()
        {
            SqlConnection con=new SqlConnection();
            con.ConnectionString="server=.;database=NHTest;uid=sa;pwd=sa;";
            SqlCommand cmd=new SqlCommand();
            cmd.Connection=con;
            cmd.CommandText="delete from students";               //清空数据库
            try
            {
                con.Open();
                cmd.ExecuteNonQuery();
            }
            finally
            {
                con.Close();
            }
        }

        [Test]
        public void TestStudentN()
        {
            Configuration cfg=new Configuration().Configure();        //直接读取hibernate.cfg.xml中的配置
            ISessionFactory factory=cfg.BuildSessionFactory();
            ITransaction tran=null;
            try
            {
                ISession session=factory.OpenSession();
                tran=session.BeginTransaction();

                StudentN newStudent=new StudentN();
                newStudent.Name="DDL";              //没有给newStudent设置Age
                session.Save(newStudent);
                tran.Commit();
            }
            catch(Exception ex)
            {
                tran.Rollback();
                throw ex;
            }

            ISession session1=factory.OpenSession();
            IList lists=session1.Find("from StudentN S where S.Name='DDL'");

            Assert.AreEqual(1,lists.Count,"名为DDL的学生没有找到");

            StudentN student=(StudentN)lists[0];

            Assert.AreEqual("DDL",student.Name,"没找到名为LLY的student");
            //Assert.AreEqual(student.Age,null);             //学生的Age不为null,不过Age的HasValue属性为false
            Assert.IsFalse(student.Age.HasValue,"Age有值");
        }

        [Test]
        public void TestStudent()                 
        {
            Configuration cfg=new Configuration().Configure();    //直接读取hibernate.cfg.xml中的配置
            ISessionFactory factory=cfg.BuildSessionFactory();
            ITransaction tran=null;
            try
            {
                ISession session=factory.OpenSession();
                tran=session.BeginTransaction();

                Student newStudent=new Student();
                newStudent.Name="LLY";               //没有给newStudent设置Age
                session.Save(newStudent);
                tran.Commit();
            }
            catch(Exception ex)
            {
                tran.Rollback();
                throw ex;
            }

            ISession session1=factory.OpenSession();
            IList lists=session1.Find("from Student S where S.Name='LLY'");

            Assert.AreEqual(1,lists.Count,"名为LLY的学生没有找到");

            Student student=(Student)lists[0];

            Assert.AreEqual("LLY",student.Name,"没找到名为LLY的student");
            Assert.AreEqual(0,student.Age,"学生年龄没有设置默认值0");
        }
    }
}