jsf - @ManyToMany的selectManyCheckbox中的LazyInitializationException(fetch = LAZY)

Question

当您需要填写JPA M:N关系时，最好的方法是处理多个hackbox。例如，我有一个JPA实体硬件和实体连接性。

硬件具有一组连通性:

private Set<Connectivity> connectivities = new HashSet<Connectivity>(0);

并具有这样的setter和getter:

@ManyToMany(fetch = FetchType.LAZY, cascade = { CascadeType.PERSIST, CascadeType.REFRESH }, mappedBy = "hwProviders")
    public Set<Connectivity> getConnectivities() {
        return this.connectivities;
    }

    public void setConnectivities(Set<Connectivity> connectivities) {
        this.connectivities = connectivities;
    }

我在具有的gui中使用JSF2.2和primefaces 5.3:

<p:selectManyCheckbox id="connectivity" value="#{hardware.connectivities}" converter="omnifaces.SelectItemsConverter" layout="pageDirection">
     <f:selectItems value="#{connectivityes}" var="connect" itemValue="#{connect}" itemLabel="#{connect.name}"/>
</p:selectManyCheckbox>

即使在渲染 View 之前打电话强行加载集合，我也会遇到延迟异常的问题:

hardware.getConnectivities().size();

有关如何处理这种情况的任何建议？

我正在使用omnifaces进行实体转换。

Tnx到BalusC我已经设法正确地进行了加载，但是在保存方面仍然存在问题。当我选中复选框并提交表单时，我在转换中得到了懒惰异常，我认为:

16:34:50,538 SEVERE [javax.enterprise.resource.webcontainer.jsf.context] (default task-12) org.hibernate.LazyInitializationException: failed to lazily initialize a collection, 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.PersistentSet.add(PersistentSet.java:202)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.convertSelectManyValuesForModel(MenuRenderer.java:381)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.convertSelectManyValue(MenuRenderer.java:128)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.getConvertedValue(MenuRenderer.java:314)
    at org.primefaces.component.selectmanycheckbox.SelectManyCheckboxRenderer.getConvertedValue(SelectManyCheckboxRenderer.java:39)
    at javax.faces.component.UIInput.getConvertedValue(UIInput.java:1045)
    at javax.faces.component.UIInput.validate(UIInput.java:975)
    at javax.faces.component.UIInput.executeValidate(UIInput.java:1248)
    at javax.faces.component.UIInput.processValidators(UIInput.java:712)
    at javax.faces.component.UIForm.processValidators(UIForm.java:253)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1260)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1260)
    at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1195)
    at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:76)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646)
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:130)
    at si.arctur.filter.SessionFilter.doFilter(SessionFilter.java:76)
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60)
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:132)
    at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:85)
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:61)
    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
    at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:56)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:45)
    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:63)
    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58)
    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:70)
    at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:261)
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:247)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:76)
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:166)
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:197)
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:759)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

您需要在事务内部(因此，在service方法内部)获取它，而在事务外部(例如，在JSF受管bean的init/action方法内部)则而不是来获取它，因此将抛出LazyInitializationException。

所以，你的尝试

hardware.getConnectivities().size();

必须在交易内部进行。如有必要，请创建新的服务方法，以使您传递之前在另一笔交易中获得的实体。

hardwareService.fetchConnectivities(hardware);

public void fetchConnectivities(Hardware hardware) {
    hardware.setConnectivities(em.merge(hardware).getConnectivities()); // Becomes managed.
    hardware.getConnectivities().size(); // Triggers lazy initialization.
}

一种替代方法是创建一个DTO，以期获得它的急切目的。

然后，要保存选择的项目，请确保您将选择组件的collectionType属性显式指定为标准Java类型，而不是让它自动发现JPA隐式特定于延迟加载的类型，例如您的特定情况下的org.hibernate.collection.internal.PersistentSet。 JSF需要它以便实例化集合，然后再用选定的项目填充它。

<p:selectManyCheckbox ... collectionType="java.util.LinkedHashSet">

另请参见org.hibernate.LazyInitializationException at com.sun.faces.renderkit.html_basic.MenuRenderer.convertSelectManyValuesForModel。