I am using hibernate to map the data from mysql database.
This is my queries :
long id = (Long) session.createQuery("Select category.id from Project as p where p.id =:projectId").setLong("projectId", projectId).uniqueResult();
activities = session.createQuery("Select name from Activity as a where a.parent.id =:activityId").setLong("activityId", id).list();
It works fine. How can I merge these two queries to one query?
addenda
Activity class:
@Entity
public class Activity implements BaseEntry, Comparable<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;
@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;
Project class:
@Entity
public class Project implements BaseEntry, Comparable<Project> {
private static final long serialVersionUID = 1911160043392595450L;
@Id
@GeneratedValue
private long id;
@Column(name = "short", unique = true, nullable = false)
private String key;
@Column(nullable = false)
private String name;
@ManyToOne(optional = false, fetch = FetchType.EAGER)
private Activity category;
I used:
activities = session.createQuery("Select a.name from Activity as a where a.parent.id = (Select p.category.id from Project as p where p.id =:projectId)")
.setLong("projectId", projectId).list();
And got an Error:
Apache Tomcat/7.0.23 – Error report
HTTP Status 500 –
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.codehaus.jackson.map.JsonMappingException: could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->se.softwerk.timelog.model.Activity["parent"]->se.softwerk.timelog.model.Activity_$$_javassist_3["id"])
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)
root cause
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)
note The full stack trace of the root cause is available
The simpliest way to merge these queries is to use a subquery: