无法写内容：懒得初始化角色集合 [英] Could not write content: failed to lazily initialize a collection of role

问题描述

我有一对多的关系，这是我的代码

I have One-To-Many relationship, here is my code

@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：
无法写内容：懒得初始化$ b的集合$ b role：com.example.helios.model.Catalog.items，无法初始化
代理 - 没有Session;嵌套异常是
com.fasterxml.jackson.databind.JsonMappingException：懒得
初始化一个角色集合：
com.example.helios.model.Catalog.items，无法初始化代理 -
没有Session
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.writeWithMessageConverters（AbstractMessageConverterMethodProcessor.java:222）
org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor .handleReturnValue（HttpEntityMethodProcessor.java:183）
org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue（HandlerMethodReturnValueHandlerComposite.java:80）
o rg.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle（ServletInvocableHandlerMethod.java:126）

org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: failed to lazily initialize a collection of role: com.example.helios.model.Catalog.items, could not initialize proxy - no Session; nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.example.helios.model.Catalog.items, could not initialize proxy - no Session 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.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:222) org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:183) org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:80) org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:126)

我的版本是：

• SpringFramework 4.2.4.RELEASE


• Hibernate 4.3.11.Final


• Jackson 2.7.4


• Jacksontype 2.7.1

• SpringFramework 4.2.4.RELEASE
• Hibernate 4.3.11.Final
• Jackson 2.7.4
• Jacksontype 2.7.1

推荐答案

这是正常的Hibernate行为

This is the normal Hibernate behaviour

在一对多关系中，hibernate加载父实体（在你的情况下为Catalog）但它会在LAZY模式下加载子实体列表（在您的情况下列出项目和列表顺序）

In one to many relations, hibernate loads the father entity (Catalog in your case) but it will load the children entities List (List items and List orders in your case) in a LAZY mode

这意味着您无法访问这些对象，因为它们只是代理和不是真实的对象

This means you can't access to these objects because they are just proxies and not real objects

这是有用的，以避免在执行查询时加载完整的数据库

This is usefull in order to avoid to load the full DB when you execute a query

你有2个解决方案：

1. 在EAGER模式下加载子实体（我强烈建议你o不能这样做，因为你可以加载完整的数据库....但它与你的场景有关。


2. 你没有使用com在你的JSON中序列化子实体。 fasterxml.jackson.annotation.JsonIgnore property

Angelo

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