上一篇：NHibernate學習筆記（一）：初識NHibernate

本文的內容：
１．介紹NH如何處理對象間one-to-ont的映射關系；

經驗教訓：
１．操作一對一關聯關系中的一個對象時，得在程序中指定如何與另一個對象關聯，如在Student類中寫this.NativePlace.Student = this；
２．在為類寫映射文件時，必須指定類的具體的名稱空間，若則運行時會出現＂找不到＊＊＊映射文件＂的問題；
　　這兩點都困擾了我好長一段時間，應該要引起注意．

點擊下載本文相關代碼（可在上篇代碼的基礎上做修改）
one-to-one：
NH中處理一對一關聯的方式有兩種：
１．主鍵關聯
２．惟一外鍵關聯

本文使用主鍵關聯處理一對一的關系。

　　主鍵關聯不需要額外的表字段；兩行是通過這種一對一關系相關聯的，那么這兩行就共享同樣的主關鍵字值。所以如果你希望兩個對象通過主鍵一對一關聯，你必須確認它們被賦予同樣的標識值！

　　持久化對象之間一對一的關聯關系是通過one-to-one元素定義的。 <one-to-one
????name="propertyName"(1)
????class="ClassName"(2)
????cascade="all|none|save-update|delete"(3)
????constrained="true|false"(4)
????outer-join="true|false|auto"(5)
????property-ref="propertyNameFromAssociatedClass"?(6)
????access="field|property|ClassName"(7)
/>

　　以下是對one-to-one元素各屬性的說明：
　　１．name：屬性的名字
　　２．class：(可選 - 默認是通過反射得到的屬性類型): 被關聯的類的名字
　　３．cascade：(可選) 表明操作是否從父對象級聯到被關聯的對象
　　４．constrained：(可選) 表明該類對應的表對應的數據庫表，和被關聯的對象所對應的數據庫表之間，通過一個外鍵引用對主鍵進行約束。這個選項影響Save()和Delete()在級聯執行時的先后順序（也在schema export tool中被使用）
　　５．outer-join：(可選 - 默認為 auto):當設置hibernate.use_outer_join的時候，對這個關聯允許外連接抓取
　　６．property-ref：(可選): 指定關聯類的一個屬性，這個屬性將會和本外鍵相對應。如果沒有指定，會使用對方關聯類的主鍵
　　７．access：(可選 - defaults to property): NHibernate 用來訪問屬性的策略

本文所涉及的類說明：
其中BizObject、User、ObjectBroker、Sessions等四個類就是NHibernate學習筆記（一）：初識NHibernate這篇文章定義的。
Student類和NativePlace類是一對一的雙向關聯關系：類Student通過屬性NativePlace關聯類NativePlace;類NativePlace通過屬性Student關聯類Student。

類Student的代碼如下： using?System;
using?System.Collections.Generic;
using?System.Text;

namespace?NHibernateTest
{
????public?class?Student?:?User
????{
????????fields#region?fields
????????private?NativePlace?objNativePlace;
????????#endregion

????????constructors#region?constructors
????????public?Student()
????????{
????????????objNativePlace?=?new?NativePlace();
????????}

????????public?Student(int?StudentID)?:?base(StudentID)?{?}
????????#endregion

????????properties#region?properties
????????public?NativePlace?NativePlace
????????{
????????????get
????????????{
????????????????return?objNativePlace;
????????????}
????????????set
????????????{
????????????????objNativePlace?=?value;
????????????}
????????}
????????#endregion

????????methors#region?methors
????????public?bool?addNewStudent()
????????{
????????????try
????????????{
????????????????this.NativePlace.Student?=?this;
????????????????this.Create();
????????????????return?true;
????????????}
????????????catch?(Exception?e)
????????????{
????????????????return?false;
????????????}
????????}

????????public?bool?deleteStudent()
????????{
????????????try
????????????{
????????????????this.NativePlace.Student?=?this;
????????????????this.Delete();
????????????????return?true;
????????????}
????????????catch?(Exception?e)
????????????{
????????????????return?false;
????????????}
????????}

????????public?bool?updateStudent()
????????{
????????????try
????????????{
????????????????this.NativePlace.Student?=?this;
????????????????this.Update();
????????????????return?true;
????????????}
????????????catch?(Exception?e)
????????????{
????????????????return?false;
????????????}
????????}
????????#endregion
????}
}

　　在每次操作Student對象時，都得指定NativePlace.Student，如：this.NativePlace.Student = this;如果沒寫這一行運行時會出現“could not find class:NativePlace”（我就在寫卡了好久）

類NativePlace的代碼如下： using?System;
using?System.Collections.Generic;
using?System.Text;

namespace?NHibernateTest
{
????public?class?NativePlace?:?BizObject
????{
????????fields#region?fields
????????private?int?intNPID;
????????private?string?strCity;
????????private?string?strProvince;
????????private?Student?objStudent;
????????#endregion

????????properties#region?properties
????????public?int?NPID
????????{
????????????get
????????????{
????????????????return?intNPID;
????????????}
????????????set
????????????{
????????????????intNPID?=?value;
????????????}
????????}

????????public?Student?Student
????????{
????????????get
????????????{
????????????????return?objStudent;
????????????}
????????????set
????????????{
????????????????objStudent?=?value;
????????????}
????????}

????????public?string?Province
????????{
????????????get
????????????{
????????????????return?strProvince;
????????????}
????????????set
????????????{
????????????????strProvince?=?value;
????????????}
????????}

????????public?string?City
????????{
????????????get
????????????{
????????????????return?strCity;
????????????}
????????????set
????????????{
????????????????strCity?=?value;
????????????}
????????}
????????#endregion
????}
}

　　這兩個類的定義相對于User類沒有什么太大的區別，接下來介紹兩個類的配置文件。

　　從ＵＭＬ來看，類NativePlace與類User之間是集合（構成）關系，即類NativePlace屬于類Student的一部分，但不能獨立存在，也就是說類NativePlace是依賴于類User的。

數據庫腳本： --表Users：用于保存Student對象
Create?Table?[Users]
(
??[ID]?int?identity(1,1)?constraint?PK_UserID1?Primary?Key,
??[UserName]?varchar(20)?not?null,
??[Password]?varchar(20)?not?null
)

--表NativePlace：用于保存NativePlace對象
Create?Table?NativePlace
(
??--表NativePlace與表Users通過主鍵關聯，則需保證兩表的主鍵名一致
??ID?int?Constraint?PK_NativePlaceID?Primary?Key,????
??Province?varchar(50),
??City?varchar(50)
)
類Student的映射文件： <?xml?version="1.0"?encoding="utf-8"??>
<hibernate-mapping?xmlns="urn:nhibernate-mapping-2.0">
??<class?name="NHibernateTest.Student,NHibernateTest"?table="Users">
????<id?name="UserID"?column="ID"?type="Int32"?unsaved-value="0">
??????<generator?class="identity"/>
????</id>
????<property?name="UserName"?column="UserName"?type="String"?length="20"/>
????<property?name="Password"?column="Password"?type="String"?length="20"/>
????
????<one-to-one?name="NativePlace"?class="NHibernateTest.NativePlace,NHibernateTest"?cascade="all"?/>
??</class>
</hibernate-mapping>

類NativePlace的映射文件： <?xml?version="1.0"?encoding="utf-8"??>
<hibernate-mapping?xmlns="urn:nhibernate-mapping-2.0">
??<class?name="NHibernateTest.NativePlace,NHibernateTest"?table="NativePlace">
????<id?name="NPID"?column="ID"?type="Int32"?unsaved-value="0">
??????<generator?class="foreign">
????????<param?name="property">Student</param>
??????</generator>
????</id>
????<property?name="Province"?column="Province"?type="String"?length="50"/>
????<property?name="City"?column="City"?type="String"?length="50"/>
????
????<one-to-one?name="Student"?class="NHibernateTest.Student,NHibernateTest"?cascade="all"?constrained="true"></one-to-one>
??</class>
</hibernate-mapping>
注意：如果采用<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">這種聲明的話，請在之后指寫相關聯類的名字時請指出完整的類名（名稱空間+類名）和程序集名：如<class name="NHibernateTest.NativePlace,NHibernateTest" table="NativePlace">和<one-to-one name="Student" class="NHibernateTest.Student,NHibernateTest" cascade="all" constrained="true"></one-to-one>

接下來是測試類：
using?System;
using?System.Collections.Generic;
using?System.ComponentModel;
using?System.Data;
using?System.Drawing;
using?System.Text;
using?System.Windows.Forms;

namespace?NHibernateTest
{
????public?partial?class?frmStudent?:?Form
????{
????????public?frmStudent()
????????{
????????????InitializeComponent();
????????}

????????Student?objStudent;

????????//Add?New?Student
????????private?void?button1_Click(object?sender,?EventArgs?e)
????????{
????????????objStudent?=?new?Student();

????????????objStudent.UserName?=?"jailu";
????????????objStudent.Password?=?"123";
????????????objStudent.NativePlace.Province?=?"FuJian";
????????????objStudent.NativePlace.City?=?"LongYan";

????????????if?(objStudent.addNewStudent())
????????????{
????????????????MessageBox.Show("Success");
????????????}
????????????else
????????????{
????????????????MessageBox.Show("UnSuccess");
????????????}
????????}

????????//Update
????????private?void?btnUpdate_Click(object?sender,?EventArgs?e)
????????{
????????????objStudent.UserName?=?"Update?UserName";
????????????objStudent.NativePlace.Province?=?"Update?Province";

????????????if?(objStudent.updateStudent())
????????????{
????????????????MessageBox.Show("Success");
????????????}
????????????else
????????????{
????????????????MessageBox.Show("UnSuccess");
????????????}
????????}

????????//Delete
????????private?void?btnDelete_Click(object?sender,?EventArgs?e)
????????{
????????????if?(objStudent.deleteStudent())
????????????{
????????????????MessageBox.Show("Success");
????????????}
????????????else
????????????{
????????????????MessageBox.Show("UnSuccess");
????????????}
????????}
????}
}
　　所有的類和映射文件都寫好了，運行．．．成功．

轉載于:https://www.cnblogs.com/jailu/archive/2006/06/29/438463.html

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