01-04-02【Nhibernate (版本3.3.1.4000) 出入江湖】HQL查询

         public IList<Customer> GetAllHql()
         {
             IList<Customer> result = null;
             ISession session = _sessionManager.GetSession();

             try
             {

                 result = session.CreateQuery("from Customer").List<Customer>();
             }
             catch (Exception)
             {
                 throw;
             }
             finally
             {
                 session.Close();
             }

             return result;
         }

注意：

result = session.CreateQuery("from Customer").List<Customer>();

Customer是类名，而不是数据库表名。

这正是Nhibernate的好处：屏蔽对数据库的底层操作，直接面向对象（实体类）编程。

实例：

         public IList<Customer> GetAllCustomers_HQL(){
            return session.CreateQuery("from Customer  c").List<Customer>();
         }

         public IList<int> GetCustomerId_HQL() {
             return session.CreateQuery("select c.CustomerId from Customer c").List<int>();
         }

         public IList<Object[]> GetCustomerInfo_HQL() {
             return session.CreateQuery("select c.FirstName,count(c.FirstName) from Customer c group by c.FirstName").List<Object[]>();
         }

         public IList<Object[]> AggregateFunction()
         {
             return session.CreateQuery("select avg(c.CustomerId),sum(c.CustomerId),count(c) from Customer c")
                 .List<Object[]>();
         }

         public IList<String> Distinct_HQL() {
             return session.CreateQuery("select distinct c.FirstName from Customer c").List<String>();
         }

         public IList<Customer> Where_HQL() {
             return session.CreateQuery("from Customer c where c.FirstName='aaaa'").List<Customer>();
         }

         public IList<Customer> Where_HQL(String firstname)
         {
             String hql = String.Format("from Customer c where c.FirstName='{0}'",firstname);
             return session.CreateQuery(hql).List<Customer>();
         }

         public IList<Customer> WhereLike_HQL(String firstname)
         {
             String hql = String.Format("from Customer c where c.FirstName like'%{0}%'", firstname);
             return session.CreateQuery(hql).List<Customer>();
         }

         public IList<Customer> WhereLike_HQL2(String firstname)
         {
             String hql = "from Customer c where c.FirstName like ?";
             return session.CreateQuery(hql).SetString(,"%"+firstname+"%").List<Customer>();
         }

         public IList<Customer> WhereLike_HQL3(String firstname)
         {
             String hql = "from Customer c where c.FirstName like :fname";
             return session.CreateQuery(hql).SetString("fname", "%" + firstname + "%").List<Customer>();
         }

         public IList<Customer> OrderBy_HQL() {
             return session.CreateQuery("from Customer c order by c.FirstName asc,c.LastName desc").List<Customer>();
         }

         //查询下定单的客户信息
         public IList<Customer> InnerJoin_HQL()
         {
             string hql = "select distinct a from Customer a inner join a.Orders b ";
             return session.CreateQuery(hql).List<Customer>();
         }

         //public IList<Customer> UseCriteriaAPI_GetCustomersWithOrders(DateTime orderDate)(){
         //      return null;
         //}

         //查询下定单的客户信息()
         public IList<Customer> InnerJoin_HQL(String orderDate)
         {
             string hql = "select distinct a from Customer a inner join a.Orders b where b.OrderDate>:orderDate";
             return session.CreateQuery(hql).SetString("orderDate",orderDate).List<Customer>();
         }

------------------------------------------------------------------------------
HQL查询返回不规则对象：                   

        /// <summary>
        /// HQL返回不规则对象
        /// </summary>
        /// <param name="orderDate"></param>
        /// <returns></returns>
        public IList<Object[]> GetObjectByHQL(String orderDate)
        {
            //Object的成员依次是Customer，OrderDate
            string hql = "select distinct a,b.OrderDate from Customer a " +
                         "inner join a.Orders b where b.OrderDate=:orderDate";
            return _session.CreateQuery(hql)
                .SetString("orderDate", orderDate)
                .List<Object[]>();
        }

Object的成员依次是Customer，OrderDate，

            IList<Object[]> objects = customerService.GetObjectByHQL(order1.OrderDate.ToString());

            foreach (var objectse in objects)
            {
                Console.WriteLine("{0}---{1}",
                    ((Customer)objectse[]).CustomerId,
                    objectse[objectse.Length-].ToString());
            }

调用者必须知道Object的成员及其类型，才能正确使用查询结果，这样很不好。

改进的做法是：
    创建一个类Object的成员类型，将HQL返回不规则对象转化为通用对象，减低调用着使用的的复杂度

    public class HQLQueryResult
    {
        public Customer Customer { get; set; }
        public DateTime OrderDate { get; set; }
    }

        /// <summary>
        /// 将HQL返回不规则对象转化为通用对象，减低调用着使用的的复杂度
        /// </summary>
        /// <param name="orderDate"></param>
        /// <returns></returns>
        public IList<HQLQueryResult> GetObjectByHQLAndTransferToEasyObject(String orderDate)
        {
            List<HQLQueryResult> results = new List<HQLQueryResult>();
            //Object的成员依次是Customer，OrderDate
            string hql = "select distinct a,b.OrderDate from Customer a " +
                         "inner join a.Orders b where b.OrderDate=:orderDate";
            IList<Object[]> objects =_session.CreateQuery(hql).SetString("orderDate", orderDate).List<Object[]>();
            foreach (var objectse in objects)
            {
               HQLQueryResult tmp = new HQLQueryResult()
               {
                    Customer= ((Customer)objectse[]),
                    OrderDate = (DateTime)objectse[objectse.Length - ]
               };

               results.Add(tmp);
            }
            return results;
        }

调用者可以这要调用：

            IList<HQLQueryResult> objects = customerService.GetObjectByHQLAndTransferToEasyObject(order1.OrderDate.ToString());

            foreach (var objectse in objects)
            {
                Console.WriteLine("{0}---{1}",
                    objectse.Customer.CustomerId,
                    objectse.OrderDate.ToString());
            }