Description
This is because the saveXWikiCollection method calls getxWikiClass which in turn tries to load the same document which haven't been saved yet...
The error we get is:
com.xpn.xwiki.XWikiException: Error number 3202 in 3: Exception while reading document Blog.Categories Wrapped Exception: a different object with the same identifier value was already associated with the session: [com.xpn.xwiki.doc.XWikiDocument#2090668008] at com.xpn.xwiki.store.XWikiHibernateStore.loadXWikiDoc(XWikiHibernateStore.java:596) at com.xpn.xwiki.store.XWikiCacheStore.loadXWikiDoc(XWikiCacheStore.java:158) at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1101) at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1143) at com.xpn.xwiki.XWiki.getClass(XWiki.java:5359) at com.xpn.xwiki.objects.BaseCollection.getxWikiClass(BaseCollection.java:126) at com.xpn.xwiki.store.XWikiHibernateStore.saveXWikiCollection(XWikiHibernateStore.java:734) at com.xpn.xwiki.store.XWikiHibernateStore.saveXWikiDoc(XWikiHibernateStore.java:434) at com.xpn.xwiki.store.XWikiCacheStore.saveXWikiDoc(XWikiCacheStore.java:97) at com.xpn.xwiki.store.XWikiCacheStore.saveXWikiDoc(XWikiCacheStore.java:91) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1077) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1050) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1044) at com.xpn.xwiki.plugin.packaging.Package.installDocument(Package.java:591) at com.xpn.xwiki.plugin.packaging.Package.install(Package.java:520) at com.xpn.xwiki.tool.backup.Importer.importDocuments(Importer.java:77) at com.xpn.xwiki.tool.backup.ImportMojo.execute(ImportMojo.java:64) at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:549) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:544) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:332) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:149) at org.apache.maven.DefaultMaven.execute_aroundBody0(DefaultMaven.java:223) at org.apache.maven.DefaultMaven.execute_aroundBody1$advice(DefaultMaven.java:304) at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:1) at org.apache.maven.embedder.MavenEmbedder.execute_aroundBody4(MavenEmbedder.java:880) at org.apache.maven.embedder.MavenEmbedder.execute_aroundBody5$advice(MavenEmbedder.java:304) at org.apache.maven.embedder.MavenEmbedder.execute(MavenEmbedder.java:1) at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:176) at org.apache.maven.cli.MavenCli.main(MavenCli.java:63) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:585) at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289) at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229) at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:408) at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:351) Wrapped Exception: org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [com.xpn.xwiki.doc.XWikiDocument#2090668008] at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:150) at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:195) at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:103) at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:878) at org.hibernate.impl.SessionImpl.load(SessionImpl.java:784) at com.xpn.xwiki.store.XWikiHibernateStore.loadXWikiDoc(XWikiHibernateStore.java:491) at com.xpn.xwiki.store.XWikiCacheStore.loadXWikiDoc(XWikiCacheStore.java:158) at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1101) at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1143) at com.xpn.xwiki.XWiki.getClass(XWiki.java:5359) at com.xpn.xwiki.objects.BaseCollection.getxWikiClass(BaseCollection.java:126) at com.xpn.xwiki.store.XWikiHibernateStore.saveXWikiCollection(XWikiHibernateStore.java:734) at com.xpn.xwiki.store.XWikiHibernateStore.saveXWikiDoc(XWikiHibernateStore.java:434) at com.xpn.xwiki.store.XWikiCacheStore.saveXWikiDoc(XWikiCacheStore.java:97) at com.xpn.xwiki.store.XWikiCacheStore.saveXWikiDoc(XWikiCacheStore.java:91) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1077) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1050) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1044) at com.xpn.xwiki.plugin.packaging.Package.installDocument(Package.java:591) at com.xpn.xwiki.plugin.packaging.Package.install(Package.java:520) at com.xpn.xwiki.tool.backup.Importer.importDocuments(Importer.java:77) at com.xpn.xwiki.tool.backup.ImportMojo.execute(ImportMojo.java:64) at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:549) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:544) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:332) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:149) at org.apache.maven.DefaultMaven.execute_aroundBody0(DefaultMaven.java:223) at org.apache.maven.DefaultMaven.execute_aroundBody1$advice(DefaultMaven.java:304) at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:1) at org.apache.maven.embedder.MavenEmbedder.execute_aroundBody4(MavenEmbedder.java:880) at org.apache.maven.embedder.MavenEmbedder.execute_aroundBody5$advice(MavenEmbedder.java:304) at org.apache.maven.embedder.MavenEmbedder.execute(MavenEmbedder.java:1) at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:176) at org.apache.maven.cli.MavenCli.main(MavenCli.java:63) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:585) at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289) at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229) at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:408) at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:351) com.xpn.xwiki.XWikiException: Error number 3202 in 3: Exception while reading document Blog.Categories Wrapped Exception: a different object with the same identifier value was already associated with the session: [com.xpn.xwiki.doc.XWikiDocument#2090668008] at com.xpn.xwiki.store.XWikiHibernateStore.loadXWikiDoc(XWikiHibernateStore.java:596) at com.xpn.xwiki.store.XWikiCacheStore.loadXWikiDoc(XWikiCacheStore.java:158) at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1101) at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1143) at com.xpn.xwiki.XWiki.getClass(XWiki.java:5359) at com.xpn.xwiki.objects.BaseCollection.getxWikiClass(BaseCollection.java:126) at com.xpn.xwiki.store.XWikiHibernateStore.saveXWikiCollection(XWikiHibernateStore.java:734) at com.xpn.xwiki.store.XWikiHibernateStore.saveXWikiDoc(XWikiHibernateStore.java:434) at com.xpn.xwiki.store.XWikiCacheStore.saveXWikiDoc(XWikiCacheStore.java:97) at com.xpn.xwiki.store.XWikiCacheStore.saveXWikiDoc(XWikiCacheStore.java:91) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1077) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1050) at com.xpn.xwiki.XWiki.saveDocument(XWiki.java:1044) at com.xpn.xwiki.plugin.packaging.Package.installDocument(Package.java:591) at com.xpn.xwiki.plugin.packaging.Package.install(Package.java:520) at com.xpn.xwiki.tool.backup.Importer.importDocuments(Importer.java:77) at com.xpn.xwiki.tool.backup.ImportMojo.execute(ImportMojo.java:64) at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:549) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:544) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:332) at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:149) at org.apache.maven.DefaultMaven.execute_aroundBody0(DefaultMaven.java:223) at org.apache.maven.DefaultMaven.execute_aroundBody1$advice(DefaultMaven.java:304) at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:1) at org.apache.maven.embedder.MavenEmbedder.execute_aroundBody4(MavenEmbedder.java:880) at org.apache.maven.embedder.MavenEmbedder.execute_aroundBody5$advice(MavenEmbedder.java:304) at org.apache.maven.embedder.MavenEmbedder.execute(MavenEmbedder.java:1) at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:176) at org.apache.maven.cli.MavenCli.main(MavenCli.java:63) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:585) at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289) at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229) at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:408) at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:351)
Note that we have 2 such documents in XE: Blog.Categories and XWiki.XWikiPreferences