NHibernate初学三之条件查询(Criteria Queries)与AspNetPager分页实例

NHibernate除了SQL与HQL两种查询操作外，还有一种就是条件查询Criteria，本文将从网上整理一些Criteria的理论及小实例，最后通过一个结合AspNetPager分页来加深理解，必竟分页这种功能在平时的项目中还是经常需要；

一：条件查询(Criteria Queries)理论

为了对应HQL的种种查询条件，NHibernate预定义了大量的Expression方法，列几个如下：

Eq = Equal
Gt = Greater than
Lt = Less than
Like = Like
Not = Not
IsNull = Is Null

1.1 条件查询(Criteria Queries)：具有一个直观的、可扩展的条件查询API是NHibernate的特色。NHibernate.ICriteria接口表示特定持久类的一个查询。ISession是 ICriteria 实例的工厂。

//创建关联到某个类的查询对象
ICriteria criteria = session.CreateCriteria(typeof(Person));
//添加表达式
criteria.Add(Expression.Eq("Name","Jackie Chan"));
IList list = criteria.List();

Eq是Equal的缩写，意思是添加一个查询表达式，Person.Name = “Jackie Chan”
对应HQL就是：from Person p where p.Name=”Jackie Chan”

1.1.1 经常还有一个实体里面有多条件查询，也可以如下面写法，简单地new出一个person对象，然后填充其属性即可，不用再去构造那丑陋的条件判断语句了：

ICriteria criteria = session.CreateCriteria(typeof(Person));
Person person = new Person();
person.Name = "Jackie Chan";
person.Age = 50;
//创建一个Example对象
criteria.Add(Example.Create(person));
IList list = criteria.List();

1.2 限制结果集内容:一个单独的查询条件是NHibernate.Expression.ICriterion 接口的一个实例。NHibernate.Expression.Expression类 定义了获得某些内置ICriterion类型的工厂方法。

IList cats = sess.CreateCriteria(typeof(Cat))
    .Add( Expression.Like("Name", "Fritz%") )
    .Add( Expression.Between("Weight", minWeight, maxWeight) )
    .List();

1.2.1 约束可以按逻辑分组

IList cats = sess.CreateCriteria(typeof(Cat))
    .Add( Expression.Like("Name", "Fritz%") )
    .Add( Expression.Or(
        Expression.Eq( "Age", 0 ),
        Expression.IsNull("Age")
    ) )
    .List();


IList cats = sess.CreateCriteria(typeof(Cat))
    .Add( Expression.In( "Name", new String[] { "Fritz", "Izi", "Pk" } ) )
    .Add( Expression.Disjunction()
        .Add( Expression.IsNull("Age") )
        .Add( Expression.Eq("Age", 0 ) )
        .Add( Expression.Eq("Age", 1 ) )
        .Add( Expression.Eq("Age", 2 ) )
    ) )
    .List();

1.2.2 允许你直接使用SQL,{alias}占位符应当被替换为被查询实体的列别名

IList cats = sess.CreateCriteria(typeof(Cat))
            .Add( Expression.Sql("lower({alias}.Name) like lower(?)", "Fritz%", NHibernateUtil.String )
            .List();

1.3 结果集排序:可以使用NHibernate.Expression.Order来为查询结果排序,其方法有两个Order.Asc()及Order.Desc()

IList cats = sess.CreateCriteria(typeof(Cat))
    .Add( Expression.Like("Name", "F%")
    .AddOrder( Order.Asc("Name") )
    .AddOrder( Order.Desc("Age") )
    .SetMaxResults(50)
    .List();

1.4 限制记录范围

ICriteria criteria = session.CreateCriteria(typeof(Person));
//从第10条记录开始取
criteria.SetFirstResult(10);
//取20条记录
criteria.SetMaxResults(20);
IList list = criteria.List();

 

二：Criteria结合AspNetPager分页实例

分页功能基本上在第一个项目都会出现，能过本实例完成一个简单的分页功能，本文把主要代码贴出来，完整的源代码文章最后提供下载；

2.1 创建一个T_School的表，并创建一个存储过程用于循环插入数据进行分页，脚本如下：

CREATE TABLE [dbo].[T_School](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [SchoolName] [nvarchar](255) COLLATE Chinese_PRC_CI_AS NULL,
    [BuildDate] [datetime] NULL,
    [Address] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL,
    [IsSenior] [bit] NULL,
    [StudentNum] [int] NULL,
 CONSTRAINT [PK_T_School] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

Create PROCEDURE [dbo].[Pro_Insert]
AS
declare @ID int
BEGIN
 set @ID=0
 while @ID<200000
 begin
 insert into T_School(SchoolName,BuildDate,Address,IsSenior,StudentNum) VALUES('中学教育'+cast(@ID as varchar),'2014/3/4 21:49:32','厦门软件园',1,390)
 set @ID=@ID+1
 end
END

2.2 在实体层简单定义几个分页要用到的类，对一些属性进行封装，下面只是PageInfo类，其它类的代码大家直接查看源代码；

namespace Wujy.ModelLibrary.Pagination
{
    public class PageInfo
    {
        public PageInfo() { }

        public PageInfo(Type entityType,int pageIndex) 
        {
            this._entityType = entityType;
            this._pageIndex = pageIndex;
        }

        public PageInfo(Type entityType, int pageIndex,params NCondition[] conditions)
        {
            this._entityType = entityType;
            this._pageIndex = pageIndex;
            this._conditions = conditions;
        }

        public PageInfo(Type entityType, int pageIndex, NCondition[] conditions,NOrder[] orders)
        {
            this._entityType = entityType;
            this._pageIndex = pageIndex;
            this._conditions = conditions;
            this._orderFields = orders;
        }

        private Type _entityType;//类

        public Type EntityType
        {
            get { return _entityType; }
            set { _entityType = value; }
        }
        private int _pageIndex = 1;//页号

        public int PageIndex
        {
            get { return _pageIndex; }
            set { _pageIndex = value; }
        }

        private NCondition[] _conditions;//条件

        public NCondition[] Conditions
        {
            get { return _conditions; }
            set { _conditions = value; }
        }
        private NOrder[] _orderFields;//排序

        public NOrder[] OrderFields
        {
            get { return _orderFields; }
            set { _orderFields = value; }
        }
        private int pageSize = 10;

        public int PageSize
        {
            get { return pageSize; }
            set { pageSize = value; }
        }


        private int _recordCount;

        public int RecordCount
        {
            get { return _recordCount; }
            set { _recordCount = value; }
        }
        private int pageCount;

        public int PageCount
        {
            get { return pageCount; }
            set { pageCount = value; }
        }
        private System.Collections.IList list;

        public IList List
        {
            get { return list; }
            set { list = value; }
        }
    }
}

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