JPA中的映射集合

CollectionModel.java

  

import hibernate.pojo.annotation.Image;

  

import java.util.ArrayList;

import java.util.Collection;

import java.util.HashMap;

import java.util.HashSet;

import java.util.List;

import java.util.Map;

import java.util.Set;

  

import javax.persistence.Column;

import javax.persistence.ElementCollection;

import javax.persistence.Embeddable;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.MapKeyColumn;

import javax.persistence.Table;

  

import org.hibernate.annotations.CollectionId;

import org.hibernate.annotations.GenericGenerator;

import org.hibernate.annotations.IndexColumn;

import org.hibernate.annotations.OrderBy;

import org.hibernate.annotations.Type;

  

@Entity

@Table(name = "collection")

@GenericGenerator(name = "nat", strategy = "increment")

public class CollectionModel {

    @Id

    @GeneratedValue(generator = "nat")

    private long id;

  

    private String name;

      

    /**

     * 对于@ElementCollection中targetClass代表的是collection类型，

     * 如果显示指定了collection类型，则hibernate不会自动侦测元素类型，此时必须告诉

     * 告诉hiberate应以何种type解析collection包含元素,

     * targetClass默认为集合类型,所以也可以写成@ElementCollection即可,

     * 如果没有显示指定集合类型，则可以省略@ElementCollection

     * 对于@JoinColumn属性nullable应该设为nullable = false，保证关联表数据保持一致

     */

    @ElementCollection(targetClass = java.lang.String.class)

    @JoinTable(name = "item", joinColumns = { @JoinColumn(nullable = false, name = "item_id", referencedColumnName = "id") })

    @Column(name = "filename", nullable = false)

    private Set<String> images = new HashSet<String>();

  

    /**

     * 

     * 插入list集合

     * 【list集合中需要额外加入@IndexColumn】来建立一个序列标识符，

     * 如果无@IndexColumn，则会当做一个包集合处理，

     * 相当于xml中的<bag></bag>标签

     */

      

    @ElementCollection(targetClass = java.lang.String.class)

    @JoinTable(name = "item", joinColumns = { @JoinColumn(nullable = false, name = "item_id") })

    @IndexColumn(name = "position", base = 1)

    /* 此处为list-index标识 位置 */

    @Column(name = "filename", nullable = false)

    @OrderBy(clause="item_id desc")

    private List<String> listImages = new ArrayList<String>();

      

    /**

     * 

     * 插入map集合

     * map集合中加入特殊的@MapKeyColumn

     */

    @ElementCollection

    @JoinTable(name="item", joinColumns={ @JoinColumn(nullable=false, name="item_id")})

    @MapKeyColumn(name="map_key")

    @Column(name="filename", nullable=false)

    private Map<String, String> mapImages = new HashMap<String, String>();

      

    /**

     * 

     *以一个组件的方式插入list中

     *以组件作为collection类型，此时作为类型的组件应该@Embeddable标记

     *private Collection<Image> list = new ArrayList<Image>();

     *如果此处改为private List<Image> list = new ArrayList<Image>();

     *则在组件所对应的表中，如果是复合主键，则需要让每一个主键都不能为空，如果其中有主键可以为空，那复合

     *主键的意义就不存在了

     *就如<bag></bag>和<idbag></idbag>标签类似，

     *可以加入一个代理主键【@CollectionId】,这样就不必限制符合主键内每个都不能

     *为空了，@CollectionId的generator属性不能为"native"

     */

    @ElementCollection

    @JoinTable(name="item_image", joinColumns= {@JoinColumn(nullable = false, name ="item_id")})

    @CollectionId(columns={@Column(name="item_auto_id")}, type=@Type(type="long"), generator="nat")

    private Collection<Image> list = new ArrayList<Image>();

  

    public long getId() {

        return id;

    }

  

    public void setId(long id) {

        this.id = id;

    }

  

    public String getName() {

        return name;

    }

  

    public void setName(String name) {

        this.name = name;

    }

  

    public Set<String> getImages() {

        return images;

    }

  

    public void setImages(Set<String> images) {

        this.images = images;

    }

  

    public List<String> getListImages() {

        return listImages;

    }

  

    public void setListImages(List<String> listImages) {

        this.listImages = listImages;

    }

  

    public Map<String, String> getMapImages() {

        return mapImages;

    }

  

    public void setMapImages(Map<String, String> mapImages) {

        this.mapImages = mapImages;

    }

  

    public Collection<Image> getList() {

        return list;

    }

  

    public void setList(Collection<Image> list) {

        this.list = list;

    }

}

  

  

  

Image.java

  

import javax.persistence.Column;

import javax.persistence.Embeddable;

  

@Embeddable

public class Image {

    private String filename;

      

    @Column(name="size_x")

    private int sizeX;

      

    @Column(name="size_y")

    private int sizeY;

  

    public boolean equals(Object obj) {

        if (!(obj instanceof Image))

            return false;

        Image image = (Image) obj;

        if ((image.getFilename().equals(this.getFilename()))

                && (image.sizeX == this.getSizeX())

                && image.getSizeY() == this.getSizeY()

                )

            return true;

        else return false;

    }

  

    public int hashCode() {

        // TODO Auto-generated method stub

        return 0;

    }

  

    public String getFilename() {

        return filename;

    }

  

    public void setFilename(String filename) {

        this.filename = filename;

    }

  

    public int getSizeX() {

        return sizeX;

    }

  

    public void setSizeX(int sizeX) {

        this.sizeX = sizeX;

    }

  

    public int getSizeY() {

        return sizeY;

    }

  

    public void setSizeY(int sizeY) {

        this.sizeY = sizeY;

    }

}

  

  

Test:

  

public class CollectionTest {

    public static void main(String[] args) {

        CollectionModel model = new CollectionModel();

        model.setName("李四");

        /*插入数据

//      Set<String> set = new HashSet<String>();

//      set.add("lisi -1");

//      set.add("lisi -1");

//      model.setImages(set);

//      List<String> list = new ArrayList<String>();

//      list.add("张三");

//      list.add("李四");

//      list.add("王五");

//      model.setListImages(list);

        */

        /**

         * 针对map的测试类

         */

        /*Map<String, String> map = new HashMap<String,String>();

        map.put("key1", "value1");

        map.put("key2", "value2");

        map.put("key3", "value3");

        model.setMapImages(map);

         */

        List<Image> list = new ArrayList<Image>();

        Image image = new Image();

        image.setFilename("file1");

        image.setSizeX(20);

        image.setSizeY(30);

        list.add(image);

          

        image = new Image();

        image.setFilename("file2");

        image.setSizeX(40);

        image.setSizeY(50);

        list.add(image);

        model.setList(list);

        JPASessionFactory.persistenceObject(model);

    }

  

}

 

描述：Ⅰ.Hibernate annotations 对包含值类型的集合映射支持非标准的注解. 对于值类型的对象不具备数据库的同一性，它属于一个实体的实例，值类型的类没有标识符或者标识属性，值类型的实例的生命周期由所依附的实体实例的生命周期所决定，且值类型的对象不支持共享引用。