NHibernate的关联映射(one-to-one,one-to-many,many-to-many)以及cascade分析
一、典型设置
cascade：（默认为none）级联。指明哪些操作会从对象级联到关联的对象。
inverse： (默认为false) 标记这个集合作为双向关联关系中的方向一端。在双向关联时才需要设置。在设为false的一端对cascade进行维护。处于性能的考虑，一般在数据少的 一端或者被依赖端设置inverse="true",而让数据多的一段维护cascade。
1.one-to-one
1.1 数据库表结构
其中T_Person为主表，T_Employee为子表。T_Employee的PersonId参照T_Peson的PersonId。
1.2 示例映射类文件
/*
/*作者：DDL/*联系：http://renrenqq.cnblogs.com/
*/
using System;namespace DDLLY.TestNHibernate.TestAssociation.OneToOne{
/// <summary> /// 
/// </summary> [Serializable] public class Person {
Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _personid; private string _name; private Employee _employee; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Person() { _personid = 0; _name = null; _employee = null; } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int PersonId { get { return _personid; } set { _isChanged |= (_personid != value); _personid = value; } } /// <summary> /// /// </summary> public virtual string Name { get { return _name; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Name", value, value.ToString()); _isChanged |= (_name != value); _name = value; } } /// <summary> /// /// </summary> public Employee Employee { get { return _employee; } set { _employee = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Person castObj = (Person) obj; return (castObj != null) && (_personid == castObj.PersonId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_personid.GetHashCode(); return hash; } #endregion }}/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;namespace DDLLY.TestNHibernate.TestAssociation.OneToOne{ /// <summary> /// /// </summary> [Serializable] public class Employee { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _personid; private string _job; private Person _person; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Employee() { _personid = 0; _job = null; _person = null; } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int PersonId { get { return _personid; } set { _isChanged |= (_personid != value); _personid = value; } } /// <summary> /// /// </summary> public virtual string Job { get { return _job; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Job", value, value.ToString()); _isChanged |= (_job != value); _job = value; } } public Person Person { get { return _person; } set { _person = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Employee castObj = (Employee) obj; return (castObj != null) && (_personid == castObj.PersonId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_personid.GetHashCode(); return hash; } #endregion }}1.3 示例映射文件
<?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToOne.Person,DDLLY.TestNHibernate.TestAssociation" table="T_Person"> <id name="PersonId" column="PersonId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="Name" type="String" name="Name" length="64" /> <one-to-one name="Employee" class="DDLLY.TestNHibernate.TestAssociation.OneToOne.Employee,DDLLY.TestNHibernate.TestAssociation" cascade="all"></one-to-one> </class></hibernate-mapping><?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToOne.Employee,DDLLY.TestNHibernate.TestAssociation" table="T_Employee"> <id name="PersonId" column="PersonId" type="Int32" unsaved-value="0"> <generator class="foreign"> <param name="property">Person</param> </generator> </id> <property column="Job" type="String" name="Job" length="64" /> <one-to-one name="Person" class="DDLLY.TestNHibernate.TestAssociation.OneToOne.Person,DDLLY.TestNHibernate.TestAssociation" constrained="true"></one-to-one> </class></hibernate-mapping>1.4 说明
constrained（约束）: 表明该类对应的表对应的数据库表，和被关联的对象所对应的数据库表之间，通过一个外键引用对主键进行约束。这个选项影响Save()和Delete()在级联执行时的先后顺序（也在schema export tool中被使用）。
property-ref: (可选) 指定关联类的一个属性，这个属性将会和本外键相对应。如果没有指定，会使用对方关联类的主键。
- <generator class="foreign">:表示使用另外一个相关联的对象的标识符，来创建主健。T_Employee的PersonId来自T_Person的ParentId。
Employee依赖于Person,所以通常在Person设置cascade。
2.另一种one-to-one
2.1数据库表结构
其中T_Person1为主表，T_Employee1为子表。T_Employee1的PersonId设置唯一约束，参照T_Person1的PersonId。
2.2示例映射类文件
/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;namespace DDLLY.TestNHibernate.TestAssociation.OneToOne1{ /// <summary> /// /// </summary> [Serializable] public class Person { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _personid; private string _name; private Employee _employee; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Person() { _personid = 0; _name = null; _employee = null; } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int PersonId { get { return _personid; } set { _isChanged |= (_personid != value); _personid = value; } } /// <summary> /// /// </summary> public virtual string Name { get { return _name; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Name", value, value.ToString()); _isChanged |= (_name != value); _name = value; } } /// <summary> /// /// </summary> public Employee Employee { get { return _employee; } set { _employee = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Person castObj = (Person) obj; return (castObj != null) && (_personid == castObj.PersonId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_personid.GetHashCode(); return hash; } #endregion }}
/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;namespace DDLLY.TestNHibernate.TestAssociation.OneToOne1{ /// <summary> /// /// </summary> [Serializable] public class Employee { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _employeeId; private string _job; private Person _person; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Employee() { _employeeId = 0; _job = null; _person = null; } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int EmployeeId { get { return _employeeId; } set { _isChanged |= (_employeeId != value); _employeeId = value; } } /// <summary> /// /// </summary> public virtual string Job { get { return _job; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Job", value, value.ToString()); _isChanged |= (_job != value); _job = value; } } public Person Person { get { return _person; } set { _person = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Employee castObj = (Employee) obj; return (castObj != null) && (_employeeId == castObj.EmployeeId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_employeeId.GetHashCode(); return hash; } #endregion }}
2.3示例映射文件
<?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToOne1.Person,DDLLY.TestNHibernate.TestAssociation" table="T_Person1"> <id name="PersonId" column="PersonId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="Name" type="String" name="Name" length="64" /> <one-to-one name="Employee" class="DDLLY.TestNHibernate.TestAssociation.OneToOne1.Employee,DDLLY.TestNHibernate.TestAssociation" cascade="all"></one-to-one> </class></hibernate-mapping><?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToOne1.Employee,DDLLY.TestNHibernate.TestAssociation" table="T_Employee1"> <id name="EmployeeId" column="EmployeeId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="Job" type="String" name="Job" length="64" /> <many-to-one name="Person" class="DDLLY.TestNHibernate.TestAssociation.OneToOne1.Person,DDLLY.TestNHibernate.TestAssociation" column="PersonId" unique="true"></many-to-one> </class></hibernate-mapping>2.4说明
这种one-to-one实际上是一种特殊的one-to-many,如果T_Employee1的PersonId不设置唯一约束，则可成为 one-to-many。所以在T_Employee端设置many-to-one而不是one-to-one,记住要加上unique="true"表 示唯一约束。
3.one-to-many
3.1 数据库表结构
T_Parent为主表，T_Child的ParentId参照T_Parent的ParentId。
注意:对于单向的one-to-many映射,cascade过程中会用到把T_Child表的ParentId设置为Null,所以ParentId应设为允许NULL;
而双向one-to-many映射,建议把T_Child的ParentI设置为不允许NULL
3.2 示例映射类文件(单向)
/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;using System.Collections;namespace DDLLY.TestNHibernate.TestAssociation.OneToMany1{ /// <summary> /// /// </summary> [Serializable] public class Parent { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _parentid; private string _name; private IList _children; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Parent() { _parentid = 0; _name = null; _children = new ArrayList(); } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int ParentId { get { return _parentid; } set { _isChanged |= (_parentid != value); _parentid = value; } } /// <summary> /// /// </summary> public virtual string Name { get { return _name; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Name", value, value.ToString()); _isChanged |= (_name != value); _name = value; } } /// <summary> /// /// </summary> public virtual IList Children { get { return _children; } set { _isChanged |= (_children != value); _children = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Parent castObj = (Parent) obj; return (castObj != null) && (_parentid == castObj.ParentId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_parentid.GetHashCode(); return hash; } #endregion }}/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;namespace DDLLY.TestNHibernate.TestAssociation.OneToMany1{ /// <summary> /// /// </summary> [Serializable] public class Child { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _childid; private string _name; private int _parentid; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Child() { _childid = 0; _name = null; _parentid = 0; } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int ChildId { get { return _childid; } set { _isChanged |= (_childid != value); _childid = value; } } /// <summary> /// /// </summary> public virtual string Name { get { return _name; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Name", value, value.ToString()); _isChanged |= (_name != value); _name = value; } } /// <summary> /// /// </summary> public virtual int ParentId { get { return _parentid; } set { _isChanged |= (_parentid != value); _parentid = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Child castObj = (Child) obj; return (castObj != null) && (_childid == castObj.ChildId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_childid.GetHashCode(); return hash; } #endregion }}3.3 示例映射文件（单向）
<?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToMany1.Parent,DDLLY.TestNHibernate.TestAssociation" table="T_Parent"> <id name="ParentId" column="ParentId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="Name" type="String" name="Name" length="64" /> <bag name="Children" cascade="all" lazy="true"> <key column="ParentId"/> <one-to-many class="DDLLY.TestNHibernate.TestAssociation.OneToMany1.Child,DDLLY.TestNHibernate.TestAssociation"/> </bag> </class></hibernate-mapping><?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToMany1.Child,DDLLY.TestNHibernate.TestAssociation" table="T_Child"> <id name="ChildId" column="ChildId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="Name" type="String" name="Name" length="64" /> <property column="ParentId" type="Int32" name="ParentId"/> </class></hibernate-mapping>3.4 示例映射类文件(双向)
/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;using System.Collections;namespace DDLLY.TestNHibernate.TestAssociation.OneToMany{ /// <summary> /// /// </summary> [Serializable] public class Parent { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _parentid; private string _name; private IList _children; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Parent() { _parentid = 0; _name = null; _children = new ArrayList(); } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int ParentId { get { return _parentid; } set { _isChanged |= (_parentid != value); _parentid = value; } } /// <summary> /// /// </summary> public virtual string Name { get { return _name; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Name", value, value.ToString()); _isChanged |= (_name != value); _name = value; } } /// <summary> /// /// </summary> public virtual IList Children { get { return _children; } set { _isChanged |= (_children != value); _children = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Parent castObj = (Parent) obj; return (castObj != null) && (_parentid == castObj.ParentId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_parentid.GetHashCode(); return hash; } #endregion }}/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;namespace DDLLY.TestNHibernate.TestAssociation.OneToMany{ /// <summary> /// /// </summary> [Serializable] public class Child { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _childid; private string _name; private Parent _parent; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Child() { _childid = 0; _name = null; _parent = null; } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int ChildId { get { return _childid; } set { _isChanged |= (_childid != value); _childid = value; } } /// <summary> /// /// </summary> public virtual string Name { get { return _name; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Name", value, value.ToString()); _isChanged |= (_name != value); _name = value; } } /// <summary> /// /// </summary> public virtual Parent Parent { get { return _parent; } set { _isChanged |= (_parent != value); _parent = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Child castObj = (Child) obj; return (castObj != null) && (_childid == castObj.ChildId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_childid.GetHashCode(); return hash; } #endregion }}3.5 示例映射类文件(双向)
<?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToMany.Parent,DDLLY.TestNHibernate.TestAssociation" table="T_Parent"> <id name="ParentId" column="ParentId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="Name" type="String" name="Name" length="64" /> <bag name="Children" cascade="all" inverse="true" lazy="true"> <key column="ParentId"/> <one-to-many class="DDLLY.TestNHibernate.TestAssociation.OneToMany.Child,DDLLY.TestNHibernate.TestAssociation"/> </bag> </class></hibernate-mapping><?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.OneToMany.Child,DDLLY.TestNHibernate.TestAssociation" table="T_Child"> <id name="ChildId" column="ChildId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="Name" type="String" name="Name" length="64" /> <many-to-one name="Parent" column="ParentId" class="DDLLY.TestNHibernate.TestAssociation.OneToMany.Parent,DDLLY.TestNHibernate.TestAssociation" /> </class></hibernate-mapping>3.6 说明
在NHibernate配置文件中使用<set>, <list>, <map>, <bag>, <array> 和 <primitive-array>等元素来定义集合。<bag>是典型的一个，代码中我们用IList和它对应。我们以后会详 细讲集合这个话题。
lazy表示允许延迟加载。表示在需要使用时才加载需要的数据。例如使用lazy时我们Load一个Parent他的Children为空，只有我 们访问它的某一个Child时数据才会被加载；而不设置lazy我们Load一个Parent时其Children将同时加载。注意：使用lazy加载必 须保证对应ISession的打开，否则懒加载会失败。
one-to-many可以设置单向和双向映射，设置单向时Child一段不设置many-to-one，而设置了ParentId的属性。
双向映射需要设置inverse而单向不需要。
单项映射在cascade时会对把T_Child的ParentId使用Update为Null的操作。
建议尽量使用双向映射。
4.many-to-many
4.1 数据库表结构
4.2 示例映射类文件
/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;using System.Collections;namespace DDLLY.TestNHibernate.TestAssociation.ManyToMany{ /// <summary> /// /// </summary> [Serializable] public class User { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _userid; private string _username; private string _password; private string _email; private IList _roles; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public User() { _userid = 0; _username = null; _password = null; _email = null; _roles = new ArrayList(); } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int UserId { get { return _userid; } set { _isChanged |= (_userid != value); _userid = value; } } /// <summary> /// /// </summary> public virtual string UserName { get { return _username; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for UserName", value, value.ToString()); _isChanged |= (_username != value); _username = value; } } /// <summary> /// /// </summary> public virtual string Password { get { return _password; } set { if (value != null) if (value.Length > 32) throw new ArgumentOutOfRangeException("Invalid value for Password", value, value.ToString()); _isChanged |= (_password != value); _password = value; } } /// <summary> /// /// </summary> public virtual string Email { get { return _email; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for Email", value, value.ToString()); _isChanged |= (_email != value); _email = value; } } public IList Roles { get { return _roles; } set { _roles = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; User castObj = (User) obj; return (castObj != null) && (_userid == castObj.UserId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_userid.GetHashCode(); return hash; } #endregion }}/*/*作者：DDL/*联系：http://renrenqq.cnblogs.com/*/using System;using System.Collections;namespace DDLLY.TestNHibernate.TestAssociation.ManyToMany{ /// <summary> /// /// </summary> [Serializable] public class Role { Private Members Private Members private bool _isChanged; private bool _isDeleted; private int _roleid; private string _rolename; private IList _users; #endregion Default ( Empty ) Class Constuctor Default ( Empty ) Class Constuctor /// <summary> /// default constructor /// </summary> public Role() { _roleid = 0; _rolename = null; _users = new ArrayList(); } #endregion // End of Default ( Empty ) Class Constuctor Public Properties Public Properties /// <summary> /// /// </summary> public virtual int RoleId { get { return _roleid; } set { _isChanged |= (_roleid != value); _roleid = value; } } /// <summary> /// /// </summary> public virtual string RoleName { get { return _rolename; } set { if (value != null) if (value.Length > 64) throw new ArgumentOutOfRangeException("Invalid value for RoleName", value, value.ToString()); _isChanged |= (_rolename != value); _rolename = value; } } public IList Users { get { return _users; } set { _users = value; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsChanged { get { return _isChanged; } } /// <summary> /// Returns whether or not the object has changed it's values. /// </summary> public bool IsDeleted { get { return _isDeleted; } } #endregion Public Functions Public Functions /// <summary> /// mark the item as deleted /// </summary> public void MarkAsDeleted() { _isDeleted = true; _isChanged = true; } #endregion Equals And HashCode Overrides Equals And HashCode Overrides /// <summary> /// local implementation of Equals based on unique value members /// </summary> public override bool Equals(object obj) { if (this == obj) return true; if ((obj == null) || (obj.GetType() != GetType())) return false; Role castObj = (Role) obj; return (castObj != null) && (_roleid == castObj.RoleId); } /// <summary> /// local implementation of GetHashCode based on unique value members /// </summary> public override int GetHashCode() { int hash = 57; hash = 27*hash*_roleid.GetHashCode(); return hash; } #endregion }}4.3 示例映射文件
<?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.ManyToMany.User,DDLLY.TestNHibernate.TestAssociation" table="T_User"> <id name="UserId" column="UserId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="UserName" type="String" name="UserName" not-null="true" length="64" /> <property column="Password" type="String" name="Password" not-null="true" length="32" /> <property column="Email" type="String" name="Email" length="64" /> <bag name="Roles" table="T_User_Role" lazy="true"> <key column="UserId"/> <many-to-many class="DDLLY.TestNHibernate.TestAssociation.ManyToMany.Role,DDLLY.TestNHibernate.TestAssociation" column="RoleId"/> </bag> </class></hibernate-mapping><?xml version="1.0" encoding="utf-8" ?><hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"> <class name="DDLLY.TestNHibernate.TestAssociation.ManyToMany.Role,DDLLY.TestNHibernate.TestAssociation" table="T_Role"> <id name="RoleId" column="RoleId" type="Int32" unsaved-value="0"> <generator class="native"/> </id> <property column="RoleName" type="String" name="RoleName" not-null="true" length="64" /> <bag name="Users" table="T_User_Role" lazy="true" inverse="true"> <key column="RoleId"/> <many-to-many class="DDLLY.TestNHibernate.TestAssociation.ManyToMany.User,DDLLY.TestNHibernate.TestAssociation" column="UserId"/> </bag> </class></hibernate-mapping>4.4 说明
many-to-many性能不佳，数据量大时应尽可能避免使用。并尽可能使用lazy="true"。
在数据量少的一端设置inverse="true"，让数据量多的一段维护cascade。
二、cascade分析
1.总述
cascade：（默认为none）级联。指明哪些操作会从对象级联到关联的对象。
orphans：孤儿,没有夫对象的子对象。对于代码Child.Parent==null,对于数据库T_Child表中ParentId为Null的数据。
delete orphans表示cascade时删除孤儿。
一般系统中是不允许孤儿存在的，我们可以通过数据库的约束来限制孤儿，例如T_Child的ParentId设为Not NULL。
如果确实存在孤儿请考虑适合的cascade策略。
| cascade类型 | 对应操作 |
| all | Save / Delete / Update |
| all-delete-orphan | Save / Delete / Update + delete orphans |
| delete-orphan | Delete + delete orphans |
| none | No Cascades |
| delete | Delete |
| save-update | Save / Update |
2.one-to-one
a.初始化数据
| PersonId | Name | Job |
| 1 | DDL | 编程 |
| 2 | LLY | NULL |
b.测试方法
TestAddPersonWithAddEmployee
Person person = new Person();person.Name = "newPerson";Employee employee = new Employee();employee.Job = "newJob";person.Employee = employee;employee.Person = person;session.Save(person);TestUpdatePersonWithAddEmployee
Person person = session.Load(typeof (Person), 2) as Person;person.Employee = new Employee();person.Employee.Person = person;person.Employee.Job = "LLYJob";session.Update(person);TestUpdatePersonWithUpdateEmployee
Person person = session.Load(typeof (Person), 1) as Person;person.Employee.Job = "DDL'New Job";session.Update(person);TestDeletePersonWithDeleteEmployee
Person person = session.Load(typeof (Person), 1) as Person;session.Delete(person);c.测试结果
| 测试方法 | save-update | delete | delete-orphan | all | all-delete-orphan | none |
| TestAddPersonWithAddEmployee | Y | N | N | Y | Y | N |
| TestUpdatePersonWithAddEmployee | Y | N | N | Y | Y | N |
| TestUpdatePersonWithUpdateEmployee | Y | Y | Y | Y | Y | Y |
| TestDeletePersonWithDeleteEmployee | N | Y | Y | Y | Y | N |
2.另一种one-to-one
a.初始化数据
| PersonId | Name | EmployeeId | Job |
| 1 | DDL | 1 | 编程 |
| 2 | LLY | NULL | NULL |
b.测试方法
TestAddPersonWithAddEmployee
不支持
TestUpdatePersonWithAddEmployee
Person person = session.Load(typeof (Person), 2) as Person;person.Employee = new Employee();person.Employee.Person = person;person.Employee.Job = "LLYJob";session.Update(person);session.Flush();TestUpdatePersonWithUpdateEmployee
Person person = session.Load(typeof (Person), 1) as Person;person.Employee.Job = "DDL'New Job";session.Update(person);session.Flush();TestDeletePersonWithDeleteEmployee
Person person = session.Load(typeof (Person), 1) as Person;session.Delete(person);session.Flush();c.测试结果
| 测试方法 | save-update | delete | delete-orphan | all | all-delete-orphan | none |
| TestAddPersonWithAddEmployee | 不支持 | 不支持 | 不支持 | 不支持 | 不支持 | 不支持 |
| TestUpdatePersonWithAddEmployee | Y | N | N | Y | Y | N |
| TestUpdatePersonWithUpdateEmployee | Y | Y | Y | Y | Y | Y |
| TestDeletePersonWithDeleteEmployee | N | Y | Y | Y | Y | N |
3.one-to-many(双向)
a.初始化数据
| ParentId | ParentName | ChildId | ChildName |
| 1 | Parent1 | 1 | Child1 |
| 2 | Parent2 | NULL | NULL |
b.测试方法
TestAddParentWithAddChild
Parent parent = new Parent();parent.Name = "NewParent";Child child = new Child();child.Name = "NewChild";child.Parent = parent;parent.Children.Add(child);session.Save(parent);session.Flush();TestUpdateParentWithAddChild
Parent parent = session.Load(typeof (Parent), 2) as Parent;Child child = new Child();child.Name = "NewChild";child.Parent = parent;parent.Children.Add(child);session.Update(parent);session.Flush();TestUpdateParentWithUpdateChild
Parent parent = session.Load(typeof (Parent), 1) as Parent;Child child = (Child) parent.Children[0];child.Name = "UpdateName";session.Update(parent);session.Flush();TestDeleteParentWithChild
Parent parent = session.Load(typeof (Parent), 1) as Parent;session.Delete(parent);session.Flush();c.测试结果
| 测试方法 | save-update | delete | delete-orphan | all | all-delete-orphan | none |
| TestAddParentWithAddChild | Y | N | N | Y | Y | N |
| TestUpdateParentWithAddChild | Y | N | N | Y | Y | N |
| TestUpdateParentWithUpdateChild | Y | Y | Y | Y | Y | Y |
| TestDeleteParentWithChild | N | Y | Y | Y | Y | N |
4.one-to-many(单向)
a.初始化数据
同上
b.测试方法
TestAddParentWithAddChild
不支持
TestUpdateParentWithAddChild
Parent parent = session.Load(typeof (Parent), 2) as Parent;Child child = new Child();child.Name = "NewChild";child.ParentId = parent.ParentId;parent.Children.Add(child);session.Update(parent);session.Flush();TestUpdateParentWithUpdateChild
Parent parent = session.Load(typeof (Parent), 1) as Parent;Child child = (Child) parent.Children[0];child.Name = "UpdateName";session.Update(parent);session.Flush();TestDeleteParentWithChild
Parent parent = session.Load(typeof (Parent), 1) as Parent;session.Delete(parent);session.Flush();c.测试结果
| 测试方法 | save-update | delete | delete-orphan | all | all-delete-orphan | none |
| TestAddParentWithAddChild | 不支持 | 不支持 | 不支持 | 不支持 | 不支持 | 不支持 |
| TestUpdateParentWithAddChild | Y | N | N | Y | Y | N |
| TestUpdateParentWithUpdateChild | Y | Y | Y | Y | Y | Y |
| TestDeleteParentWithChild | Parent被删除，Child成为孤儿 | Y | Y | Y | Y | Parent被删除，Child成为孤儿 |
5.many-to-many
many-to-many和别的关联映射有所不同。例子中：Role和User没有直接的依赖关系，而是通过一张中间表完成。在删除User时一般不会要求删除Role，而是删除之间的关系（即从中间表删除数据）。
a.初始化数据
| UserId | UserName | Password | RoleId | RoleName | |
| 1 | DDL | 1 | NULL | 1 | 角色1 |
| 1 | DDL | 1 | NULL | 2 | 角色2 |
| 2 | LLY | 2 | NULL | 1 | 角色1 |
| 3 | 陌生人 | 3 | NULL | NULL | NULL |
| NULL | NULL | NULL | NULL | 3 | 角色3 |
b.测试方法
TestAddRoleToUser
User user = session.Load(typeof (User), 1) as User;Role role = session.Load(typeof (Role), 3) as Role;user.Roles.Add(role);role.Users.Add(user);session.Update(user);session.Flush();TestRemoveRoleFromUser
User user = session.Load(typeof (User), 1) as User;Role role = session.Load(typeof (Role), 2) as Role;user.Roles.Remove(role);role.Users.Remove(user);session.Update(user);session.Flush(); TestUpdateUserWithRole
User user = session.Load(typeof(User), 2) as User;((Role) user.Roles[0]).RoleName = "UpdateRole";session.Update(user);session.Flush();TestDeleteUserWithSetRole
User user = session.Load(typeof (User), 1) as User;session.Delete(user);session.Flush();c.测试结果
| 测试方法 | save-update | delete | delete-orphan | all | all-delete-orphan | none |
| TestAddRoleToUser | Y | Y | Y | Y | Y | Y |
| TestRemoveRoleFromUser | Y | Y | Y | Y | Y | Y |
| TestUpdateUserWithRole | Y | Y | Y | Y | Y | Y |
| TestDeleteUserWithSetRole | N | Uer被删除,但和其有关的Role也被删除 | Uer被删除,但和其有关的Role也被删除 | Uer被删除,但和其有关的Role也被删除 | Uer被删除,但和其有关的Role也被删除 | N |
三、结论
关联是NHibernate里面功能很强的一块，但也使很容易滥用而造成引起性能或其他问题的地方。所以请慎重的使用。
在使用之前，请考虑好以下问题：
1.关系分析，一对多，多对多，还是一对一。
2.确定依赖关系，例如：Child依赖于Parent。
3.是否允许存在孤儿，例如：存在Child没有Parent（即在数据库中ParentId为Null的Child）。
4.在对等的关系中是否有主动端。例如：需要给Parent设置Child还是给Child找Parent，或者两边都可以操作。
5.关联两端可能出现的数据量以及在页面显示时是否分页。如果数据量大或者页面上需要分页显示，建议不要采用关联映射。如果数据量大，性能会不好，如果需要分页，关联所有数据似乎没有什么意思。
6.页面上可能的对象操作方法。例如：先读取一个Parent，然后添加Child，然后保存。
请根据你的情况设置关联映射，而对于cascade标准的设置可以满足绝大多数的需要，如一有特殊情况，请按照上面的分析选择合适的。
