I am using hibernate to map the data to my mysql database in a

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Editorial Team

Asked: June 11, 20262026-06-11T11:40:23+00:00 2026-06-11T11:40:23+00:00

I am using hibernate to map the data to my mysql database in a

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I am using hibernate to map the data to my mysql database in a Restful Web Service(using jersey).

This is my Activity class :

@Entity
public class Activity {

    private static final long serialVersionUID = 4937176332500551910L;

    @Id
    @GeneratedValue
    private long id;

    @Column(name = "short", unique = true, nullable = false)
    private String key;

    private String name;

    private String description;

    private float cost;

    private int orderIndex = 0;

    @ManyToOne(fetch = FetchType.LAZY)
    private Activity parent;

    @OneToMany(targetEntity = Activity.class, mappedBy = "parent", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JsonIgnore
    private Collection<Activity> children;

    @OneToMany(targetEntity = Project.class, mappedBy = "category", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JsonIgnore
    private Collection<Project> projects;

    @OneToMany(targetEntity = Task.class, mappedBy = "activity",  fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JsonIgnore
    private Collection<Task> tasks;

This query works perfect :

activities = session.createQuery("from Activity").list();

The result as a Json array is :

[{"id":100,"key":"scrum","name":"Scrum","description":"","cost":0.0,"orderIndex":1,"parent":null},{"id":101,"key":"c","name":"Consulting","description":"Just in special cases, authorized by Rüdiger after discussion with customer.","cost":990.0,"orderIndex":3,"parent":{"id":100,"key":"scrum","name":"Scrum","description":"","cost":0.0,"orderIndex":1,"parent":null}},{"id":102,"key":"d","name":"Development","description":"Usually this.","cost":690.0,"orderIndex":2,"parent":{"id":100,"key":"scrum","name":"Scrum","description":"","cost":0.0,"orderIndex":1,"parent":null}},{"id":103,"key":"sales","name":"Sales","description":"Sales related activities","cost":0.0,"orderIndex":2,"parent":null},{"id":104,"key":"doit","name":"Genomför arbeten","description":"","cost":690.0,"orderIndex":1,"parent":{"id":103,"key":"sales","name":"Sales","description":"Sales related activities","cost":0.0,"orderIndex":2,"parent":null}},{"id":105,"key":"t","name":"Traveling","description":"Travel time","cost":300.0,"orderIndex":4,"parent":{"id":100,"key":"scrum","name":"Scrum","description":"","cost":0.0,"orderIndex":1,"parent":null}},{"id":106,"key":"uni","name":"University Job","description":"Activities at university","cost":690.0,"orderIndex":3,"parent":null},{"id":107,"key":"work","name":"work","description":"One rate for everything: teaching, preparing, administration, meetings, etc.","cost":690.0,"orderIndex":1,"parent":{"id":106,"key":"uni","name":"University Job","description":"Activities at university","cost":690.0,"orderIndex":3,"parent":null}},{"id":108,"key":"v","name":"Vacation/Holidays","description":"Planned vacation (counting agains the 25 days)","cost":300.0,"orderIndex":5,"parent":{"id":100,"key":"scrum","name":"Scrum","description":"","cost":0.0,"orderIndex":1,"parent":null}}]

This query also works:

activities = session.createQuery("from Activity where id=100").list();

The result is:

[{"id":100,"key":"scrum","name":"Scrum","description":"","cost":0.0,"orderIndex":1,"parent":null}]

scrum Activity is a parent as you see.

but this query does not work :

activities = session.createQuery("from Activity where id=101").list();

Because Activity with id=101 is a kind of Child Activity.

I got this error:

<html><head><title>Apache Tomcat/7.0.23 - Error report</title><style><!--H1 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:22px;} H2 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:16px;} H3 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:14px;} BODY {font-family:Tahoma,Arial,sans-serif;color:black;background-color:white;} B {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;} P {font-family:Tahoma,Arial,sans-serif;background:white;color:black;font-size:12px;}A {color : black;}A.name {color : black;}HR {color : #525D76;}--></style> </head><body><h1>HTTP Status 500 - </h1><HR size="1" noshade="noshade"><p><b>type</b> Exception report</p><p><b>message</b> <u></u></p><p><b>description</b> <u>The server encountered an internal error () that prevented it from fulfilling this request.</u></p><p><b>exception</b> <pre>org.codehaus.jackson.map.JsonMappingException: could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]-&gt;se.softwerk.timelog.model.Activity[&quot;parent&quot;]-&gt;se.softwerk.timelog.model.Activity_$$_javassist_3[&quot;id&quot;])
    org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:218)
    org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:183)
    org.codehaus.jackson.map.ser.std.SerializerBase.wrapAndThrow(SerializerBase.java:140)
    org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:158)
    org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
    org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:446)
    org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
    org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
    org.codehaus.jackson.map.ser.std.StdContainerSerializers$IndexedListSerializer.serializeContents(StdContainerSerializers.java:122)
    org.codehaus.jackson.map.ser.std.StdContainerSerializers$IndexedListSerializer.serializeContents(StdContainerSerializers.java:71)
    org.codehaus.jackson.map.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:86)
    org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:610)
    org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:256)
    org.codehaus.jackson.map.ObjectMapper.writeValue(ObjectMapper.java:1604)
    org.codehaus.jackson.jaxrs.JacksonJsonProvider.writeTo(JacksonJsonProvider.java:558)
    com.sun.jersey.json.impl.provider.entity.JacksonProviderProxy.writeTo(JacksonProviderProxy.java:160)
    com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:306)
    com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1437)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339)
    com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:708)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
</pre></p><p><b>root cause</b> <pre>org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:149)
    org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:195)
    org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
    se.softwerk.timelog.model.Activity_$$_javassist_3.getId(Activity_$$_javassist_3.java)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    org.codehaus.jackson.map.ser.BeanPropertyWriter.get(BeanPropertyWriter.java:483)
    org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:418)
    org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
    org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
    org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:446)
    org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
    org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
    org.codehaus.jackson.map.ser.std.StdContainerSerializers$IndexedListSerializer.serializeContents(StdContainerSerializers.java:122)
    org.codehaus.jackson.map.ser.std.StdContainerSerializers$IndexedListSerializer.serializeContents(StdContainerSerializers.java:71)
    org.codehaus.jackson.map.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:86)
    org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:610)
    org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:256)
    org.codehaus.jackson.map.ObjectMapper.writeValue(ObjectMapper.java:1604)
    org.codehaus.jackson.jaxrs.JacksonJsonProvider.writeTo(JacksonJsonProvider.java:558)
    com.sun.jersey.json.impl.provider.entity.JacksonProviderProxy.writeTo(JacksonProviderProxy.java:160)
    com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:306)
    com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1437)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349)
    com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339)
    com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537)
    com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:708)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
</pre></p><p><b>note</b> <u>The full stack trace of the root cause is available in the Apache Tomcat/7.0.23 logs.</u></p><HR size="1" noshade="noshade"><h3>Apache Tomcat/7.0.23</h3></body></html>

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1 Answer

Editorial Team · Answer 1 · 2026-06-11T11:40:24+00:00

Editorial Team

2026-06-11T11:40:24+00:00Added an answer on June 11, 2026 at 11:40 am

I found the answer. The problem is here :

@ManyToOne(fetch = FetchType.LAZY)
private Activity parent;

I jsut need to use FetchType.EAGER or remove it.

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