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java - 未能延迟初始化角色集合 : could not initialize proxy - no Session error in @ManyToMany mappin annotation in Hibernate?

转载 作者：行者123 更新时间：2023-11-29 01:55:52 26 4
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您好，我是 Java 服务器端创建 JSON API 的新手，我在 hibernate 中使用 ManytoMany 映射来连接两个表。我有两个类，一个是 Product.class和 Offers.class。

Product.class

@Entity
@Table(name = "products")
public class Product {

@Column(name = "merchant_code")
private String merchant_code;

@Column(name = "branch_code")
private String branch_code;

@Column(name = "product_category_code")
private String product_category_code;

@Id @GeneratedValue
@Column(name = "product_code")
private String product_code;

@Column(name = "product_short_desc")
private String product_short_desc;

@Column(name = "product_long_desc")
private String product_long_desc;

@Column(name = "image")
private String image;

@Column(name = "price")
private String price;

@Column(name = "Active_Inactive")
private String Active_Inactive;

@ManyToMany(mappedBy = "offer_relation_code", fetch = FetchType.EAGER)
@Where(clause = "offer_type_code = 1")
private List<Offers> offer;

//here my getter setter

}

Offers.class

@Entity
@Table(name = "offers")
public class Offers {

@Id @GeneratedValue
@Column(name = "offer_code")
private int offer_code;

@Column(name = "offer_type_code")
private int offer_type_code;

@Column(name = "offer_relation_code")
private int offer_relation_code;

@Column(name = "branch_code")
private int branch_code;

@Column(name = "valid_from")
private String valid_from;

@Column(name = "valid_until")
private String valid_until;

@Column(name = "offer_value")
private int offer_value;

@Column(name = "offer_desc")
private String offer_desc;

//here my getter setter     

}

获取数据

factory = cfg.configure().addAnnotatedClass(Product.class).buildSessionFactory(registry);

    Session session = factory.openSession();
    Transaction tx = null;

    try {

        tx = session.beginTransaction();

        Criteria criteria = session.createCriteria(Product.class);
        criteria.setFetchMode("product",FetchMode.JOIN);
        Criterion merchant_code_Criterion = Restrictions.eq("merchant_code", new String(merchant_code));
        Criterion branch_code_Criterion = Restrictions.eq("branch_code", new String(branch_code));
        LogicalExpression andExp = Restrictions.and(merchant_code_Criterion,branch_code_Criterion);
        criteria.add(andExp);

        search_products = (ArrayList<Product>) criteria.list();

        tx.commit();

    } catch (HibernateException e) {
        // TODO: handle exception
        if (tx != null)
            tx.rollback();
        e.printStackTrace();
    } finally {
        session.close();
    }

我正在将 offer 表与 product 表连接起来，例如 @ManyToMany(mappedBy = "offer_relation_code", fetch = FetchType.EAGER) 正在搜索在 Google 中，许多人说不要使用 EAGER，这会导致一些问题，但是当我使用 @ManyToMany(mappedBy = "offer_relation_code", fetch = FetchType.LAZY) 显示错误，如 未能延迟初始化角色集合:无法初始化代理 - 无 session 。当我使用 EAGER 时，它工作正常，没有错误。使用 EAGER 是好是坏。任何人都可以解释一下。

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