Hibernate的集合映射

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<!-- [if !supportLists]-->节 1.01   <!-- [endif]-->映射 Set

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<!-- [if !supportLists]-->1、  <!-- [endif]-->为了隐藏 ITEM_IMAGE 为一个单独表，故在数据库设计中将 ITEM_IMAGE 的主键和外键设定都设定为 ITEM_ID, 在 Hibernate 配置文件中用 set 集合的形式加以隐藏。

<!-- [if !supportLists]-->2、  <!-- [endif]-->引文 Set 集合无法包含重复元素，因此在 ITEM_IMAGE 表中使用复合主键。

 

不可重复的元素，顺序无法保存

private Set images = new HashSet ();

< set name = "images" table = "ITEM_IMAGE" >

    < key column = "ITEM_ID" />

    < element type = "string" column = "FILENAME" not-null = "true" />

</ set >

<!-- [if !supportLists]-->节 1.02   <!-- [endif]-->映射 Bag

可重复的元素，不保存元素顺序

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private Collection images = new ArrayList ();

       < idbag name = "images" table = "ITEM_IMAGE" >

           < collection-id type = "long" column = "ITEM_IMAGE_ID" >

              < generator class = "sequence" />

           </ collection-id >

           < key column = "ITEM_ID" />

           < element type = "string" column = "FILENAME" not-null = "true" />

       </ idbag >

<!-- [if !supportLists]-->节 1.03   <!-- [endif]-->映射 List

可重复的元素，顺序可以保存

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<!-- [if !supportLists]-->1、  <!-- [endif]-->添加 POSITION 列目的是用于保存存储数据的顺序。

<!-- [if !supportLists]-->2、  <!-- [endif]-->表的主键为 ITEM_ID 和 POSITION 的复合主键。

private List images = new ArrayList();

       < list name = "images" table = "ITEM_IMAGE" >

           < key column = "ITEM_ID" />

           < list-index column = "POSITION" />

           < element type = "string" column = "FILENAME" not-null = "true" />

       </ list >

 

<!-- [if !supportLists]-->节 1.04   <!-- [endif]-->映射 Map

保存键 / 值对数据 , 顺序不可保存，为无序状态

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1 、将 ITEM_ID 和 IMAGENAME 设定为双主键。

 

 

private Map images = new HashMap ();

       < map name = "images" table = "ITEM_IMAGE" >

           < key column = "ITEM_ID" />

           < map-key type = "string" column = "IMAGENAME" />

           < element type = "string" column = "FILENAME" not-null = "true" />

       </ map >

<!-- [if !supportLists]-->节 1.05   <!-- [endif]-->排序集合 Sorted Collection

<!-- [if !supportLists]-->(a)      <!-- [endif]-->排序 Set

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Set images = new TreeSet ();

< set name = "images" table = "ITEM_IMAGE" sort = "natural" >

           < key column = "ITEM_ID" />

           < element type = "string" column = "FILENAME" not-null = "true" />

</ set >

<!-- [if !supportLists]-->(b)      <!-- [endif]-->排序 Map

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private SortedMap images = new TreeMap ();

< map name = "images" table = "ITEM_IMAGE" sort = "natural" >

           < key column = "ITEM_ID" />

           < map-key type = "string" column = "IMAGENAME" />

           < element type = "string" column = "FILENAME" not-null = "true" />

</ map >

 

 

<!-- [if !supportLists]-->节 1.06   <!-- [endif]-->有序集合 Ordered Collection

<!-- [if !supportLists]-->(a)      <!-- [endif]-->有序 Set

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private Set images = new LinkedHashSet ();

< set name = "images" table = "ITEM_IMAGE" order-by = "ITEM_ID" >

           < key column = "ITEM_ID" />

           < element type = "string" column = "FILENAME" not-null = "true" />

</ set >

<!-- [if !supportLists]-->(b)      <!-- [endif]-->有序 Map

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private Map images = new LinkedHashMap ();

< map name = "images" table = "ITEM_IMAGE" order-by = "IMAGENAME asc" >

           < key column = "ITEM_ID" />

           < map-key type = "string" column = "IMAGENAME" />

           < element type = "string" column = "FILENAME" not-null = "true" />

</ map >