在本章中,我们将介绍标准查询机制. NHibernate Query by Criteria API 允许您通过在运行时操作条件对象来构建查询.
这种方法允许您动态指定约束而无需直接字符串操作,但它不会失去HQL的大部分灵活性或功能.
另一方面,表示为条件的查询通常不如HQL中表达的查询可读.
经典条件语法是基于对象的查询API,如以下程序所示.
var customers = session.CreateCriteria().Add(Restrictions.Like("FirstName", "H%"));
正如您所见,我们正在为客户创建会话创建标准,现在我们正在为该查询添加限制对象.
这对于用户可以选择某些选项但不能选择其他选项的查询页面非常有用.
将查询构建为树类查询结构而不是HQL或LINQ更容易,您可以在WHERE子句中使用AND或OR.
使用这些标准对象添加其他限制更容易.
让我们看一个简单的例子,我们将通过 createCriteria 创建一个查询并访问条件API,然后添加一个名字以H开头的限制.
using System; using System.Data; using System.Linq; using System.Reflection; using HibernatingRhinos.Profiler.Appender.NHibernate; using NHibernate.Cfg; using NHibernate.Criterion; using NHibernate.Dialect; using NHibernate.Driver; using NHibernate.Linq; namespace NHibernateDemo { internal class Program { private static void Main() { var cfg = ConfigureNHibernate(); var sessionFactory = cfg.BuildSessionFactory(); using(var session = sessionFactory.OpenSession()) using(var tx = session.BeginTransaction()) { var customers = session.CreateCriteria() .Add(Restrictions.Like("FirstName", "H%")); foreach (var customer in customers.List ()) { Console.WriteLine(customer); } tx.Commit(); } Console.WriteLine("Press to exit..."); Console.ReadLine(); } private static Configuration ConfigureNHibernate() { NHibernateProfiler.Initialize(); var cfg = new Configuration(); cfg.DataBaseIntegration(x => { x.ConnectionStringName = "default"; x.Driver (); x.Dialect (); x.IsolationLevel = IsolationLevel.RepeatableRead; x.Timeout = 10; x.BatchSize = 10; }); cfg.SessionFactory().GenerateStatistics(); cfg.AddAssembly(Assembly.GetExecutingAssembly()); return cfg; } } }
编译并执行上述代码时,您将看到以下输出.
Herman Crooks (4ead3480-6bce-11e1-b15c-6cf049ee52be) Points: 74 HasGoldStatus: True MemberSince: 12/3/2010 12:00:00 AM (Utc) CreditRating: Neutral AverageRating: 0 Orders: Order Id: 4ead3480-6bce-11e1-b15d-6cf049ee52be Order Id: 4ead3480-6bce-11e1-b15e-6cf049ee52be Order Id: 4ead3480-6bce-11e1-b15f-6cf049ee52be Order Id: 4ead3480-6bce-11e1-b160-6cf049ee52be Order Id: 4ead3480-6bce-11e1-b161-6cf049ee52be Order Id: 4ead3480-6bce-11e1-b162-6cf049ee52be Order Id: 4ead3480-6bce-11e1-b163-6cf049ee52beHudson Bins (4ec03f80-6bce-11e1-b2b7-6cf049ee52be) Points: 56 HasGoldStatus: False MemberSince: 10/20/2008 12:00:00 AM (Utc) CreditRating: Terrible AverageRating: 0 Orders: Order Id: 4ec03f80-6bce-11e1-b2b8-6cf049ee52be Order Id: 4ec03f80-6bce-11e1-b2b9-6cf049ee52be Order Id: 4ec03f80-6bce-11e1-b2ba-6cf049ee52be Order Id: 4ec03f80-6bce-11e1-b2bb-6cf049ee52be Order Id: 4ec03f80-6bce-11e1-b2bc-6cf049ee52be Order Id: 4ec03f80-6bce-11e1-b2bd-6cf049ee52be Order Id: 4ec03f80-6bce-11e1-b2be-6cf049ee52be Order Id: 4ec03f80-6bce-11e1-b2bf-6cf049ee52beHettie Feest (4ec50240-6bce-11e1-b300-6cf049ee52be) Points: 82 HasGoldStatus: False MemberSince: 4/10/2009 12:00:00 AM (Utc) CreditRating: Neutral AverageRating: 0 Orders: Order Id: 4ec50240-6bce-11e1-b301-6cf049ee52be Order Id: 4ec50240-6bce-11e1-b302-6cf049ee52be Order Id: 4ec50240-6bce-11e1-b303-6cf049ee52bePressto exit...
让我们看看另一个简单的例子,我们将检索其名字等于"Laverne"的客户
using System; using System.Data; using System.Linq; using System.Reflection; using HibernatingRhinos.Profiler.Appender.NHibernate; using NHibernate.Cfg; using NHibernate.Criterion; using NHibernate.Dialect; using NHibernate.Driver; using NHibernate.Linq;namespace NHibernateDemo { internal class Program { private static void Main() { var cfg = ConfigureNHibernate(); var sessionFactory = cfg.BuildSessionFactory(); using(var session = sessionFactory.OpenSession()) using(var tx = session.BeginTransaction()) { var customers = session.CreateCriteria() .Add(Restrictions.Eq("FirstName", "Laverne")) .List (); foreach (var customer in customers) { Console.WriteLine(customer); } tx.Commit(); } Console.WriteLine("Press to exit..."); Console.ReadLine(); } private static Configuration ConfigureNHibernate() { NHibernateProfiler.Initialize(); var cfg = new Configuration(); cfg.DataBaseIntegration(x => { x.ConnectionStringName = "default"; x.Driver (); x.Dialect (); x.IsolationLevel = IsolationLevel.RepeatableRead; x.Timeout = 10; x.BatchSize = 10; }); cfg.SessionFactory().GenerateStatistics(); cfg.AddAssembly(Assembly.GetExecutingAssembly()); return cfg; } } }
让我们再次运行此应用程序,您将看到以下输出.
Laverne Hegmann (4e97c816-6bce-11e1-b095-6cf049ee52be) Points: 74 HasGoldStatus: True MemberSince: 4/4/2009 12:00:00 AM (Utc) CreditRating: Neutral AverageRating: 0 Orders: Order Id: 4ea14d96-6bce-11e1-b095-6cf049ee52be Order Id: 4ea14d96-6bce-11e1-b096-6cf049ee52be Order Id: 4ea14d96-6bce-11e1-b097-6cf049ee52be Order Id: 4ea14d96-6bce-11e1-b098-6cf049ee52bePressto exit...
现在,条件API的一个主要缺点是属性名称中的这些不透明字符串.因此,如果第一个名称被重构为其他名称,则重构工具不一定会拾取不透明的字符串.