尝试创建新对象并将其添加到 Arraylist 时出现 Java JPA LazyInitializationException

Question

我有一个 Java spring JPA 应用程序，它有一个 Bord 实体和一个 BordRow 实体。一个 Bord 具有多个 BordRow。现在我尝试创建一个新的 BordRow 并将其添加到 Bord 中的 BordRows 列表中。但是，我收到 LazyInitializationException。我必须如何更改代码才能创建新的 BordRow、将其保存在数据库中并返回整个 Bord 对象？参数content类似于:{title: "Test Row", bord_id: 1}

异常(exception):

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: Bord.rows, could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:606) ~[hibernate-core-5.4.6.Final.jar:5.4.6.Final]
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:218) ~[hibernate-core-5.4.6.Final.jar:5.4.6.Final]
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:585) ~[hibernate-core-5.4.6.Final.jar:5.4.6.Final]
    at org.hibernate.collection.internal.AbstractPersistentCollection.write(AbstractPersistentCollection.java:409) ~[hibernate-core-5.4.6.Final.jar:5.4.6.Final]
    at org.hibernate.collection.internal.PersistentBag.add(PersistentBag.java:383) ~[hibernate-core-5.4.6.Final.jar:5.4.6.Final]
    at WebSocketController.create(WebSocketController.java:47) ~[main/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_221]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_221]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_221]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_221]
    at org.springframework.messaging.handler.invocation.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:171) ~[spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.messaging.handler.invocation.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:120) ~[spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler.handleMatch(AbstractMethodMessageHandler.java:565) [spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.messaging.simp.annotation.support.SimpAnnotationMethodMessageHandler.handleMatch(SimpAnnotationMethodMessageHandler.java:511) [spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.messaging.simp.annotation.support.SimpAnnotationMethodMessageHandler.handleMatch(SimpAnnotationMethodMessageHandler.java:94) [spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler.handleMessageInternal(AbstractMethodMessageHandler.java:520) [spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler.handleMessage(AbstractMethodMessageHandler.java:454) [spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.messaging.support.ExecutorSubscribableChannel$SendTask.run(ExecutorSubscribableChannel.java:144) [spring-messaging-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_221]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_221]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_221]

边界类别:

@Table(name = "bords")
@Entity
public class Bord
{
    @Id
    @GeneratedValue
    private int id;

    @NotNull
    private String name;

    @Column
    private String icon;

    @Column
    private String background;

    @OneToMany(mappedBy = "bord", fetch = FetchType.LAZY)
    @JsonIgnore
    private List<BordRow> rows;

    public Bord()
    {
        rows = new ArrayList<>();
    }

    public void addRow(BordRow row)
    {
        this.rows.add(row);
    }

    // Getters and setters
}

BordRow 类:

@Entity
@Table(name = "bord_rows")
public class BordRow
{
    @Id
    @GeneratedValue
    private int id;

    @NotNull
    private String title;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "bord_id")
    @JsonIgnore
    private Bord bord;

    public BordRow(String title) {
        this.title = title;
    }

    // Getters and setters
}

WebsocketController 方法:

@MessageMapping("/bord_row/create")
@SendTo("/bord_row/created")
public Optional<Bord> create(String content) {
    JSONObject object = new JSONObject(content);
    Optional<Bord> bord = bordRepository.findById(object.getInt("bord_id"));

    if(bord.isPresent())
    {
        BordRow row = new BordRow(object.getString("title"));
        row.setBord(bord.get());
        List<BordRow> rows = bord.get().getRows();
        rows.add(row);
        bord.get().setRows(rows);
        bordRepository.save(bord.get());
    }

    return bord;
}

WebsocketController方法其他尝试:

@MessageMapping("/bord_row/create")
@SendTo("/bord_row/created")
public Optional<Bord> create(String content) {
    JSONObject object = new JSONObject(content);
    Optional<Bord> bord = bordRepository.findById(object.getInt("bord_id"));

    if(bord.isPresent())
    {
        BordRow row = new BordRow(object.getString("title"));
        row.setBord(bord.get());
        bord.get().addRow(row);
        bordRepository.save(bord.get());
    }

    return bord;
}

Answer 1

这里从数据库加载一个对象

可选 bord = bordRepository.findById(object.getInt("bord_id"))

带有 BoardRows 的列表是延迟加载的，这意味着一旦事务关闭，您将在代理上工作。这是您遇到的错误，因为您想在代理上添加一些内容。

您可以将延迟加载更改为急切加载，但由于性能原因，不建议这样做。您可以使用 EntityGraph。这些允许您加载更深的对象，即使它们是延迟加载的。

我希望这有帮助

马蒂亚斯