无法写入内容：无法延迟初始化角色集合

Question

我有一对多关系，这是我的代码

@Entity
@Table(name = "catalog")
public class Catalog {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "catalog_id")
    private int catalog_id;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "name", nullable = false)
    private String name;

    @OneToMany(mappedBy="mycatalogorder")
    private List<Order> orders;

    @OneToMany(mappedBy="mycatalog")
    private List<CatalogItem> items;

    // setters and getters
}

 @Entity
 @Table(name = "catalogitem")
 public class CatalogItem {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "catalogitem_id")
    private int catalogitem_id;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "name", nullable = false)
    private String name;

    @NotEmpty
    @Column(name = "price", nullable = false)
    private Double price;

    @OneToOne(mappedBy="ordercatalogitem", cascade=CascadeType.ALL)
    private OrderItem morderitem;

    @ManyToOne
    @JoinColumn(name="catalog_id", nullable=false)
    private Catalog mycatalog;

    // setters and getters
}

@Entity
@Table(name = "orders")
public class Order {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "order_id")
    private int order_id;

    @NotEmpty
    @Size(min = 3, max = 255)
    @Column(name = "name", nullable = false)
    private String name;

    @NotEmpty
    @Size(min = 3, max = 1024)
    @Column(name = "note", nullable = false)
    private String note;

    @Temporal(TemporalType.TIMESTAMP)
    @DateTimeFormat(pattern = "ddmmYYYY HH:mm:ss")
    @Column(name = "created", nullable = false)
    private Date created;

    @OneToMany(mappedBy="myorder")
    private Set<OrderItem> orderItems;

    @ManyToOne
    @JoinColumn(name="catalog_id", nullable=false)
    private Catalog mycatalogorder;

    @PrePersist
    protected void onCreate() {
        created = new Date();
    }

    // setters and getters
}

@Entity
@Table(name = "orderitem")
public class OrderItem {

    @Id
    @Column(name="catalogitem_id", unique=true, nullable=false)
    @GeneratedValue(generator="gen")
    @GenericGenerator(name="gen", strategy="foreign", parameters=@Parameter(name="property", value="catalogitem"))
    private int catalogitem_id;

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

    @OneToOne
    @PrimaryKeyJoinColumn
    private CatalogItem ordercatalogitem;

    @ManyToOne
    @JoinColumn(name="order_id", nullable=false)
    private Order myorder;
     // setters and getters
}

我得到了例外：

org.springframework.http.converter.HttpMessageNotWritableException：无法编写内容：无法延迟初始化角色集合：com.example.helios.model.Catalog.items，无法初始化代理-
没有会话；嵌套异常是com.fasterxml.jackson.databind.JsonMappingException：无法延迟初始化角色集合：com.example.helios.model.Catalog.items，无法初始化代理-
没有会话org.springframework.http.converter.json
.AbstractJackson2HttpMessageConverter.writeInternal（AbstractJackson2HttpMessageConverter.java:271）org.springframework.http.converter.AbstractGenericHttpMessageConverter.write（AbstractGenericHttpMessageConverter.java:100）org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor

我的版本是：

• SpringFramework 4.2.4。发布
• Hibernate4.3.11.Final
• Jackson2.7.4
• Jackson类型2.7.1

Answer 1

这是正常的hibernate行为

在一对多关系中，hibernate会以LAZY模式加载父实体（在您的情况下为目录），但会加载子实体列表（在您的情况下为列表项和列表顺序）

这意味着您无法访问这些对象，因为它们只是代理，而不是真实的对象

为了避免在执行查询时加载整个数据库，这很有用

您有2个解决方案：

1. 在EAGER模式下加载子实体（我强烈建议您不要这样做，因为您可以加载完整的数据库…。但这与您的方案有关
2. 您不会通过使用com.fasterxml.jackson.annotation.JsonIgnore属性在JSON中对子实体进行序列化