Castle ActiveRecord学习实践（7）：使用HQL查询
1．HQL概述
2．SimpleQuery查询
3．ScalarQuery查询
4．自定义查询
5．使用CallBack
一．HQL简单介绍
HQL全名是Hibernate Query Language，它是一种完全面向对象的查询语言。先来看一下HQL最基本的一些用法
1．From子句
from Post你也可以为Post起一个别名
from Post as post或者省略as
from Post post2．Select 子句
select Name,Author from Blog也可以使用elements函数来查询一个集合
select elements(blog.Posts) from Blog blog3．使用聚合函数
HQL中也可以使用一些聚合函数
select count(*) from Blog blogselect count(elements(blog.Posts)) from Blog blogHQL支持的聚合函数有
avg(
), sum(), min(), max() count(*) count(), count(distinct ), count(all)4．Where子句
from Blog blog where blog.Name = ‘Terry Lee’from Blog blog where blog.Name is not null详细可以参考http://www.hibernate.org/hib_docs/reference/en/html/queryhql.html。
二．SimpleQuery查询
SimpleQuery是一种最简单的查询，它直接处理HQL语句，并返回一个集合，没有复杂的参数处理。具体用法可以参考下例：
[ActiveRecord("Posts")]public class Post : ActiveRecordBase
{
// 
/// <summary>
/// 查询某一类别的所有Posts /// </summary> /// <param name="_strCategory">类别名称</param>
/// <returns></returns> public static Post[] GetPostsByCategory(string _strCategory) { SimpleQuery query = new SimpleQuery( typeof(Post), @"from Post post where post.Category = ?", _strCategory ); return (Post[])ExecuteQuery(query); } /// <summary> /// 查询某一时间段内发表的所有Posts /// </summary> /// <param name="start">开始时间</param> /// <param name="end">结束时间</param> /// <returns></returns> public static int[] GetPostsInterval(DateTime start,DateTime end) { SimpleQuery query = new SimpleQuery( typeof(Post),typeof(int), @"select post.Id from Post post where post.Created between ? and ?", start,end ); return (int[])ExecuteQuery(query); }
}
看一下简单的测试代码：
[Test]public void TestGetPostsByCategory(){ string StrCategory = "Castle"; IList list = (IList)Post.GetPostsByCategory(StrCategory); int expectedCount = 2; Assert.IsNotNull(list); Assert.AreEqual(expectedCount,list.Count);} [Test]public void TestGetPostsInterval(){ DateTime start = Convert.ToDateTime("2006-01-01"); DateTime end = DateTime.Now; IList list = (IList)Post.GetPostsInterval(start,end); int expectedCount = 2; Assert.IsNotNull(list); Assert.AreEqual(expectedCount,list.Count);}三．ScalarQuery查询
ScalarQuery查询也是一种简单的直接处理HQL的查询，它也没有复杂的参数处理，只不过返回的值不是集合而是单一的值，具体用法参考下例：
[ActiveRecord("Blogs")]public class Blog : ActiveRecordBase{ // /// <summary> /// 查询某作者发表的所有Posts数量 /// </summary> /// <param name="_StrAuthor">作者姓名</param> /// <returns></returns> public static int GetPostNumByAuthor(string _StrAuthor) { ScalarQuery query = new ScalarQuery( typeof(Blog), @"select count(elements(blog.Posts)) from Blog blog where blog.Author = ?", _StrAuthor ); return (int)ExecuteQuery(query); }}
看一下简单的测试代码
[Test]public void TestGetPostNumByAuthor(){ string _StrAuthor = "Terry Lee"; int result = Blog.GetPostNumByAuthor(_StrAuthor); int expectedCount = 2; Assert.AreEqual(expectedCount,result);}
四．自定义查询
在实际开发中，我们所面对的查询远不止上面所说得这么简单，有时候我们需要处理一些自定义的参数，或者执行自定义的查询语句，这时需要我们编写自定义的ActiveRecord查询，首先要添加一个类，让它继承于基类ActiveRecordBaseQuery，并覆写Execute()方法（或者实现IactiveRecordQuery接口），如下例所示
public class QueryWithNamedParameters : ActiveRecordBaseQuery{ private string _authorName = null; private int _maxResults = 2; public QueryWithNamedParameters() : base(typeof(Blog)) { } public string AuthorName { get { return _authorName; } set { _authorName = value; } } public int MaxResults { get { return _maxResults; } set { _maxResults = value; } } public override object Execute(ISession session) { String hql = "from Blog blog"; if (_authorName != null) hql += " where blog.Author = :author"; IQuery q = session.CreateQuery(hql); if (_authorName != null) q.SetString("author", _authorName); q.SetMaxResults(_maxResults); return base.GetResultsArray(typeof(Blog), q.List(), null, false); }}
使用我们自定义的类
/// <summary>/// 自定义查询/// </summary>/// <param name="authorName"></param>/// <returns></returns>public static Blog[] GetThreeBlogsFromAuthor( string authorName ){ QueryWithNamedParameters q = new QueryWithNamedParameters(); q.AuthorName = authorName; q.MaxResults = 3; return (Blog[]) ExecuteQuery(q);}
看一下简单的测试代码
[Test]public void TestCustomQuery(){ string _StrAuthor = "Terry Lee"; IList list = Blog.GetThreeBlogsFromAuthor(_StrAuthor); int expectedCount = 3; Assert.IsNotNull(list); Assert.AreEqual(expectedCount,list.Count);}五．使用CallBack
还有一种实现方式是使用Execute()方法，这种方式与我们前面所讲的自定义查询是差不多的，只不过不用增加额外的自定义类。
[ActiveRecord("Blogs")]public class Blog : ActiveRecordBase{ // /// <summary> /// 通过CallBack执行 /// </summary> /// <param name="author"></param> /// <returns></returns> public static Blog[] GetPostsFromAuthor( string author ) { return (Blog[]) Execute( typeof(Blog), new NHibernateDelegate(GetPostsFromAuthorCallback), author); } private static object GetPostsFromAuthorCallback(ISession session, object instance ) { // 创建查询 IQuery query = session.CreateQuery( "from Blog blog where blog.Author = :author" ); // 设置参数 query.SetString("author", (string) instance); // 获取结果 IList results = query.List(); // 转化结果为Array Blog[] blogs = new Blog[results.Count]; results.CopyTo(blogs, 0); // 返回结果 return blogs; }}编写测试代码
[Test]public void TestGetPostsFromAuthor(){ string _StrAuthor = "Terry Lee"; IList list = Blog.GetPostsFromAuthor(_StrAuthor); int expectedCount = 4; Assert.IsNotNull(list); Assert.AreEqual(expectedCount,list.Count);}关于使用HQL查询就介绍到这儿了，相信通过HQL查询可以解决我们开发中的绝大多数的复杂查询问题。
参考资料
文中主要内容来自于Castle的官方网站http://www.castleproject.org
