NHibernate Step By Step(7)-映射集合类型

1.Set 无序不重复对象 如ISet

2.List 可按位索引对象 如IList

3.Map 键值对象，如HashTable

4.Bag 可重复对象 如IList

5.idbag

示例

1.Set

<class name="A" table="a" lazy="false">    <id name="Id" column="id" unsaved-value="null">        <generator class="native" />    </id>    <property name="Name" column="aname" />    <set name="Items" cascade="all-delete-orphan" generic="true">        <key column="a_id" />        <one-to-many class="B" />    </set></class><class name="B" table="b" lazy="false">    <id name="Id" column="id" unsaved-value="null">        <generator class="native" />    </id>    <property name="Name" column="aname" /></class>

<key column="a_id" /> 指定了外键值

<one-to-many class="B" /> 指定集合关联

2.List

<class name="A" table="a" lazy="false">    <id name="Id" column="id" unsaved-value="null">        <generator class="native" />    </id>    <property name="Name" column="aname" />    <list name="Items" cascade="all-delete-orphan" generic="true">        <key column="a_id" />        <index column="a_idx" />        <one-to-many class="B" />    </list></class><class name="B" table="b" lazy="false">    <id name="Id" column="id" unsaved-value="null">        <generator class="native" />    </id>    <property name="Name" column="aname" /></class>

因为有索引,所以加了一个index的索引字段，这是必须的

3.Bag

  <class name="A" table="a" lazy="false">      <id name="Id" column="id" unsaved-value="null">          <generator class="native" />      </id>      <property name="Name" column="aname" />        <bag name="Items" cascade="all-delete-orphan" generic="true">          <key column="a_id" />          <one-to-many class="B" />      </bag>  </class>  <class name="B" table="b" lazy="false">      <id name="Id" column="id" unsaved-value="null">          <generator class="native" />      </id>      <property name="Name" column="aname" /></class>

4.Map

<class name="A" table="a">    <id name="Id" column="id" unsaved-value="null">        <generator class="native" />    </id>    <property name="Name" column="aname" />    <map name="Items" cascade="all-delete-orphan">        <key column="a_id" />        <index column="idx" type="String" />        <one-to-many class="B" />    </map>    <map name="SortedList" collection-type="sorted-list" sort="natural">        <key column="a_id" />        <index column="idx" type="string" />        <element column="elt" type="int" />    </map>    <map name="SortedDictionary" collection-type="sorted-dictionary" sort="natural">        <key column="a_id" />        <index column="idx" type="string" />        <element column="elt" type="int" />    </map></class><class name="B" table="b" lazy="false">    <id name="Id" column="id" unsaved-value="null">        <generator class="native" />    </id>    <property name="Name" column="aname" /></class>

(1)A与B关系

(2)element表示获取数据库字段集合，而非对象集合,如下映射的类

public class A    {        private int? _id;        private string _name;        private IDictionary<string, B> _items;        private IDictionary<string, int> _sortedList;        private IDictionary<string, int> _sortedDictionary;        public A() { }        public int? Id        {            get { return _id; }            set { _id = value; }        }        public string Name        {            get { return _name; }            set { _name = value; }        }        public IDictionary<string,B> Items        {            get { return _items; }            set { _items = value; }        }        public IDictionary<string, int> SortedList        {            get { return _sortedList; }            set { _sortedList = value; }        }        public IDictionary<string, int> SortedDictionary        {            get { return _sortedDictionary; }            set { _sortedDictionary = value; }        }    }

(3)索引

key和value肯定有索引所以要加所以字段

(4)排序

4.1 sort字段
<map name="SortedList" collection-type="sorted-list" sort="natural">

sort属性中允许的值包括 unsorted, natural和某个实现了System.Collections.IComparer的类的名称

4.2 order-by

<map name="SortedList" order-by="elt asc">

order-by属性的值是一个SQL排序子句而不是HQL的

5.idbag

<class name="A" table="a" lazy="false">    <id name="Id" column="id" unsaved-value="null">        <generator class="native" />    </id>    <property name="Name" column="aname" />    <idbag name="Items" cascade="all-delete-orphan" generic="true">        <collection-id type="Int32" column="item_id">            <generator class="increment" />        </collection-id>        <key column="a_id" />        <element type="string" />    </idbag></class>

与bag不同，多出了一个id字段,可以有效进行索引