NHibernate条件查询(Criteria Query)

典型用法：从ISession接口中创建ICriteria实例对象；在这个ICriteria实例对象上设置一个或多个表达式；要求ICriteria接口返回需要的列表，就是根据表达式从数据库中返回对象。
1.创建ICriteria实例
使用ISession接口的CreateCriteria方法创建了NHibernate.ICriteria接口一个特定的持久化类的查询实例，也可以说ISession是用来制造Criteria实例的工厂。
public IList<Customer> CreateCriteria()
{
    ICriteria crit = _session.CreateCriteria(typeof(Customer));
    crit.SetMaxResults(50);
    IList<Customer> customers = crit.List<Customer>();
    return customers;
}
例如上面的例子返回Customer对象集合，设置最大的集合数量为50条。
2.模糊查询
使用ICriteria接口提供的Add方法添加Restrictions类中约束表达式可以限制一些结果集的作用。
public IList<Customer> LikeAndBetween()
{
  IList<Customer> customers =     _session.CreateCriteria(typeof(Customer))
    .Add(Restrictions.Like("Firstname", "YJing%"))
    .Add(Restrictions.Between("Lastname", "A%", "Y%"))
        .List<Customer>();
    return customers;
}
3.结果集排序
使用ICriteria.Order对结果集排序，第二个参数true代表asc，false代表desc。例如下面例子查询Customer对象按FirstName降序、Lastname升序。
public IList<Customer> Order()
{
    return _session.CreateCriteria(typeof(Customer))
        .Add(Restrictions.Like("Firstname","Y%"))
        .AddOrder(new NHibernate.Criterion.Order("Firstname", false))
        .AddOrder(new NHibernate.Criterion.Order("Lastname", true))
        .List<Customer>();
}
4.条件查询
  /// 利用CriteriaAPI获取顾客ID大于lId小于gId的顾客        public IList<Customer> GreaterAndLetter(int lId,int gId)
 {
return _session.CreateCriteria(typeof(Customer))
  .Add(Restrictions.Gt("CustomerId", lId))//大于
  .Add(Restrictions.Eq("CustomerId", lId))//等于
  .Add(Restrictions.Or(Restrictions.Eq("CustomerId", gId), Restrictions.Lt("CustomerId", gId)))//小于等于
  .List<Customer>();
}

测试：
[TestFixture]
    public class QueryCriteriaAPIFixture
    {
        private SessionManager _helper;
        private ISession _session;
        private QueryCriteriaAPI _queryCriteriaAPI;
        [TestFixtureSetUp]
        public void TestFixtureSetup()
        {_helper = new SessionManager();}
        [SetUp]
        public void Setup()
        {
            _session = _helper.GetSession();
            _queryCriteriaAPI = new QueryCriteriaAPI(_session);
        }
 [Test]
public void CreateCriteriaTest()
{
IList<Customer> customers = _queryCriteriaAPI.CreateCriteria();
   Assert.AreEqual(5, customers.Count);
 }
[Test]
public void LikeAndBetweenTest()
{
 IList<Customer> customers = _queryCriteriaAPI. LikeAndBetween();
Assert.AreEqual(1, customers.Count);
}
 [Test]
 public void OrderTest()
 {
    IList<Customer> customers = _queryCriteriaAPI.Order();
            Assert.AreEqual(1, customers.Count);
 }
[Test]
public void GreaterAndLetterTest()
{
     IList<Customer> customers＝ _queryCriteriaAPI.GreaterAndLetter (1,4);
      foreach (Customer c in customers)
       {
         Assert.GreaterOrEqual(c.CustomerId, 1);//大于等于
         Assert.LessOrEqual(c.CustomerId, 4);//小于等于
       }
  }   
}