java - 带有 map 集合的 LazyInitializationException

Question

我知道这是一个老生常谈的问题，但我找不到解决方案。我有两个 bean，其中一个有 HashMap 集合。我在尝试阅读此集合时遇到异常。已指定映射配置来立即加载此集合。

我的环境是:

• hibernate 4.2.0
• mysql-connector-java 5.1.24

我还有两颗 bean :

public class FeaturedDoc {
    private Long id;
    private Map<Feature, Float> features;

    public FeaturedDoc() {
        features = new HashMap<Feature, Float>();
    }
   (getters and setters)
}

和

public class Feature {
    private Long id;
    private String name;
    private Long internalId;
    (getters and setters)    
}

这个bean有映射:

<class name="Feature" table="FEATURE">
    <id name="id" type="long" column="ID">
        <generator class="increment"/>
    </id>
    <property name="name" length="255" type="string" unique="true" column="NAME" index="INDEX_NAME"/>
    <property name="internalId" type="long" unique="true" not-null="false" column="INTERNAL_ID" index="INDEX_INTID"/>
    <sql-insert>insert into FEATURE (NAME, INTERNAL_ID, ID) values (?, ?, ?) on duplicate key update ID = ID</sql-insert>
</class>

<class name="FeaturedDoc" table="FEATURED_DOC">
    <id name="id" type="long" column="ID">
        <generator class="increment"/>
    </id>
    <map  name="features" table="DOC_FEATURE" cascade="all" lazy="false" fetch="join">
        <key column="ID"></key>
        <map-key-many-to-many column="FEATURE_ID" class="Feature"/>
        <element column="value" type="float"/>
    </map>
</class>

我还有 DAO 层，其方法为:

public FeaturedDoc read(long id) {
    FeaturedDoc fd = null;
    try {
        session.beginTransaction();
        fd = session.get(FeaturedDoc.class, id);
        session.getTransaction().commit();
    } catch (Exception e) {
        e.printStackTrace();
        session.getTransaction().rollback();
    } finally {
        close();
    }
    return fd;
}

当我尝试做这样的事情时:

FeaturedDoc fd = daoService.read(26);
System.out.println(fd.getFeatures());

我遇到异常

org.hibernate.LazyInitializationException: could not initialize proxy - no Session

你知道我应该如何修复这个错误吗？

Answer 1

假设其他一切都正常(在映射中)，您是否尝试过将 lazy="false" 放在 cascade="all" 之前。我发现这是我的映射中的一个问题，导致了此 LazyInitializationException 错误。

此顺序显示在以下 Hibernate 引用中:http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/collections.html