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。