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