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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _personid;
        private string _name;
        private Employee _employee;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _personid;
        private string _job;
        private Person _person;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _personid;
        private string _name;
        private Employee _employee;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _employeeId;
        private string _job;
        private Person _person;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _parentid;
        private string _name;
        private IList _children;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _childid;
        private string _name;
        private int _parentid;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _parentid;
        private string _name;
        private IList _children;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _childid;
        private string _name;
        private Parent _parent;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region 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#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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#region Private Members

        private bool _isChanged;
        private bool _isDeleted;
        private int _roleid;
        private string _rolename;
        private IList _users;

        #endregion

        Default ( Empty ) Class Constuctor#region 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#region 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#region Public Functions

        /**//// <summary>
        /// mark the item as deleted
        /// </summary>
        public void MarkAsDeleted()
        {
            _isDeleted = true;
            _isChanged = true;
        }

        #endregion

        Equals And HashCode Overrides#region 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	Email	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。

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