java - 没有使用 JPQL join fetch 的 Hibernate session

Question

我一直在尝试使用 JPQL JOIN FETCH 将实体(购买)集合获取到选定的实体(客户)，但是在我获取实体之后并且当我尝试引用该集合时，堆栈跟踪将发布在这篇文章的结尾被抛出。

这是我的实体:

@Entity
public class Customers {

    @Id
    @GeneratedValue
    private int id;

    private String name;
    private int age;

    @Column(name="spend_money")
    private Double spendMoney;

    @OneToOne(cascade=CascadeType.ALL, orphanRemoval=true)
    @JoinColumn(name="contact_id")
    private Contacts contact;

    @ManyToOne
    @JoinColumn(name="country_id")
    private Country country;

    @OneToMany(mappedBy="customer")
    private Set<Purchase> purchases;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Double getSpendMoney() {
        return spendMoney;
    }

    public void setSpendMoney(Double spendMoney) {
        this.spendMoney = spendMoney;
    }

    public Contacts getContact() {
        return contact;
    }

    public void setContact(Contacts contact) {
        this.contact = contact;
    }

    public Country getCountry() {
        return country;
    }

    public void setCountry(Country country) {
        this.country = country;
    }

    public Set<Purchase> getPurchases() {
        return purchases;
    }

    public void setPurchases(Set<Purchase> purchases) {
        this.purchases = purchases;
    }


}

以及我通过给定 ID 选择客户实体的方法:

@Override
    public Customers getCustomerLazy(int id) {
        TypedQuery<Customers> query = em.createQuery(
                "SELECT c FROM Customers c JOIN c.purchases WHERE c.id = :id",
                Customers.class);

        return query.setParameter("id", id).getSingleResult();
    }

堆栈跟踪:

SEVERE: Servlet.service() for servlet jsp threw exception
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: pl.hibernate.basics.model.Customers.purchases, could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:575)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:214)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:554)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:142)
    at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180)
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.toForEachIterator(ForEachSupport.java:348)
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.supportedTypeForEachIterator(ForEachSupport.java:224)
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:155)
    at javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:256)
    at org.apache.jsp.WEB_002dINF.views.user_jsp._jspx_meth_c_005fforEach_005f0(user_jsp.java:467)
    at org.apache.jsp.WEB_002dINF.views.user_jsp._jspService(user_jsp.java:215)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:721)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:466)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:391)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:318)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:264)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1208)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:992)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:939)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:844)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:617)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

lut 10, 2016 10:54:09 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [appServlet] in context with path [/basics] threw exception [org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: pl.hibernate.basics.model.Customers.purchases, could not initialize proxy - no Session] with root cause
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: pl.hibernate.basics.model.Customers.purchases, could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:575)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:214)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:554)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:142)
    at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180)
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.toForEachIterator(ForEachSupport.java:348)
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.supportedTypeForEachIterator(ForEachSupport.java:224)
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:155)
    at javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:256)
    at org.apache.jsp.WEB_002dINF.views.user_jsp._jspx_meth_c_005fforEach_005f0(user_jsp.java:467)
    at org.apache.jsp.WEB_002dINF.views.user_jsp._jspService(user_jsp.java:215)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:721)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:466)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:391)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:318)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:264)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1208)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:992)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:939)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:844)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:617)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

Answer 1

更新 JPQL 以 FETCH 购买集合。仅使用“JOIN FETCH”而不是“JOIN”

    TypedQuery<Customers> query = em.createQuery("SELECT c FROM Customers c JOIN FETCH c.purchases p WHERE c.id = :id",Customers.class);

“连接获取”使用单个选择来初始化值集合及其父对象。这个link解释一下获取策略。