Hibernate- failed to lazily initialize a collectio

2020-03-01 00:01发布

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问题:

I use hibernate to create a rest api. I create a method to get all items in a table.

public List<Language> getAllLanguages(Session session) {
        List<Language> languages=(List<Language>)session.createQuery("from Language").list();
        return languages;
}

This is my Language.java

public class Language  implements java.io.Serializable {


     private Integer idlanguage;
     private String language;
     private Set<Patient> patients = new HashSet<Patient>(0);

    public Language() {
    }


    public Language(String language) {
        this.language = language;
    }
    public Language(String language, Set<Patient> patients) {
       this.language = language;
       this.patients = patients;
    }

    public Integer getIdlanguage() {
        return this.idlanguage;
    }

    public void setIdlanguage(Integer idlanguage) {
        this.idlanguage = idlanguage;
    }
    public String getLanguage() {
        return this.language;
    }

    public void setLanguage(String language) {
        this.language = language;
    }
    public Set<Patient> getPatients() {
        return this.patients;
    }

    public void setPatients(Set<Patient> patients) {
        this.patients = patients;
    }

}

And this is my Patient.java

// Generated Sep 14, 2016 4:33:23 PM by Hibernate Tools 4.3.1


import beans.DiabetesType;
import beans.Illness;
import beans.Language;
import beans.Reminder;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;

/**
 * Patient generated by hbm2java
 */
public class Patient  implements java.io.Serializable {

     private Integer idpatient;
     private DiabetesType diabetesType;
     private Language language;
     private String customId;
     private String diabetesOther;
     private String firstName;
     private String lastName;
     private String userName;
     private String password;
     private Date dateCreated;
     private Date lastUpdated;
     private Set<Illness> illnesses = new HashSet<Illness>(0);
     private Set<Reminder> reminders = new HashSet<Reminder>(0);


    public Patient() {
    }

    public Patient(Integer idpatient, String password) {
        this.idpatient = idpatient;
        this.password = password;
    }    

    public Patient(DiabetesType diabetesType, Language language, String customId, String firstName, String userName, String password, Date lastUpdated) {
        this.diabetesType = diabetesType;
        this.language = language;
        this.customId = customId;
        this.firstName = firstName;
        this.userName = userName;
        this.password = password;
        this.lastUpdated = lastUpdated;
    }
    public Patient(DiabetesType diabetesType, Language language, String customId, String diabetesOther, String firstName, String lastName,  String userName, String password, Date dateCreated, Date lastUpdated, Set<Illness> illnesses, Set<Reminder> reminders) {
       this.diabetesType = diabetesType;
       this.language = language;
       this.customId = customId;
       this.diabetesOther = diabetesOther;
       this.firstName = firstName;
       this.lastName = lastName;      
       this.userName = userName;
       this.password = password;
       this.dateCreated = dateCreated;
       this.lastUpdated = lastUpdated;
       this.illnesses = illnesses;
       this.reminders = reminders;
    }

    public Integer getIdpatient() {
        return this.idpatient;
    }

    public void setIdpatient(Integer idpatient) {
        this.idpatient = idpatient;
    }
    public DiabetesType getDiabetesType() {
        return this.diabetesType;
    }

    public void setDiabetesType(DiabetesType diabetesType) {
        this.diabetesType = diabetesType;
    }
    public Language getLanguage() {
        return this.language;
    }

    public void setLanguage(Language language) {
        this.language = language;
    }
    public String getCustomId() {
        return this.customId;
    }

    public void setCustomId(String customId) {
        this.customId = customId;
    }
    public String getDiabetesOther() {
        return this.diabetesOther;
    }

    public void setDiabetesOther(String diabetesOther) {
        this.diabetesOther = diabetesOther;
    }
    public String getFirstName() {
        return this.firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return this.lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getUserName() {
        return this.userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }
    public String getPassword() {
        return this.password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
    public Date getDateCreated() {
        return this.dateCreated;
    }

    public void setDateCreated(Date dateCreated) {
        this.dateCreated = dateCreated;
    }
    public Date getLastUpdated() {
        return this.lastUpdated;
    }

    public void setLastUpdated(Date lastUpdated) {
        this.lastUpdated = lastUpdated;
    }
    public Set<Illness> getIllnesses() {
        return this.illnesses;
    }

    public void setIllnesses(Set<Illness> illnesses) {
        this.illnesses = illnesses;
    }
    public Set<Reminder> getReminders() {
        return this.reminders;
    }

    public void setReminders(Set<Reminder> reminders) {
        this.reminders = reminders;
    }
}

Important: The beans and mappings are reverse engineered from MySQL database, via NetBeans. I do not need to get any data related to patient when calling getAllLangauges. My language table has only 2 columns, idlanguage and language. Patient table has a foriegn key of language table

Before using this method in rest api , it worked perfectly without any exception. But when I used this in rest api, it created a complexity in there.

I am not using annotations in here. I used hibernate reverse engineering wizard to map above entities . This is my rest api method.

@Path("/language")
public class LanguageJSONService {

    @GET
    @Path("/getAllLanguages")
    @Produces(MediaType.APPLICATION_JSON)
    public List<Language> getAllLanguages(){
        LanguageService languageService=new LanguageService();
        List<Language> list = languageService.getAllLanguages();
        return list;
    }
}

This is the way how I call the method,

Client client = ClientBuilder.newClient();
List<Language> list = client.target("http://localhost:8080/simple_rest/rest")
                .path("/language/getAllLanguages")
                .request(MediaType.APPLICATION_JSON)
                .get(new GenericType<List<Language>>() {
                });

for (int i = 0; i < list.size(); i++) {
      System.out.println("Id - " + list.get(i).getIdlanguage() + " Language - " + list.get(i).getLanguage());
}

When I call the method ,

failed to lazily initialize a collection of role: beans.Language.patients, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->beans.Language["patients"])

is occurred.

Interestingly, if I did not close the session, then I get an output like below which is totally something else, seems like it is trying to display its foreign key tables and their foreign key tables and so on...

    [{"idlanguage":1,"language":"English","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":{"iddiabetesType":1,"type":"Sever","patients":
[{"idpatient":1,"diabetesType":

Have any ideas about this problem ?

Update

my configuration file

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <property name="show_sql">true</property>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/*****</property>
    <property name="hibernate.connection.username">*****</property>
    <property name="hibernate.c3p0.min_size">5</property>
    <property name="hibernate.c3p0.max_size">20</property>
    <property name="hibernate.c3p0.timeout">3000</property>
    <property name="hibernate.c3p0.max_statements">50</property>
    <property name="hibernate.c3p0.idle_test_period">300</property>
    <property name="hibernate.c3p0.testConnectionOnCheckout">true</property>
    <property name="hibernate.c3p0.preferredTestQuery">SELECT 1</property>
    <property name="hibernate.connection.password">************</property>
    <mapping resource="beans/Reminder.hbm.xml"/>
    <mapping resource="beans/Food.hbm.xml"/>
    <mapping resource="beans/Patient.hbm.xml"/>
    <mapping resource="beans/Illness.hbm.xml"/>
    <mapping resource="beans/Language.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

Language.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Sep 14, 2016 4:33:23 PM by Hibernate Tools 4.3.1 -->
<hibernate-mapping>
    <class name="beans.Language" table="language" catalog="myglukose" optimistic-lock="version">
        <id name="idlanguage" type="java.lang.Integer">
            <column name="idlanguage" />
            <generator class="identity" />
        </id>
        <property name="language" type="string">
            <column name="language" length="45" not-null="true" />
        </property>
        <set name="patients" table="patient" inverse="true" lazy="true" fetch="select">
            <key>
                <column name="language_idlanguage" not-null="true" />
            </key>
            <one-to-many class="beans.Patient" />
        </set>
    </class>
</hibernate-mapping>

This is my patient mapping file,

Patient.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Sep 14, 2016 4:33:23 PM by Hibernate Tools 4.3.1 -->
<hibernate-mapping>
    <class name="beans.Patient" table="patient" catalog="myglukose" optimistic-lock="version">
        <id name="idpatient" type="java.lang.Integer">
            <column name="idpatient" />
            <generator class="identity" />
        </id>
        <many-to-one name="diabetesType" class="beans.DiabetesType" fetch="select">
            <column name="diabetes_type_iddiabetes_type" not-null="true" />
        </many-to-one>
        <many-to-one name="language" class="beans.Language" fetch="select">
            <column name="language_idlanguage" not-null="true" />
        </many-to-one>
        <property name="customId" type="string">
            <column name="custom_id" length="45" not-null="true" />
        </property>
        <property name="diabetesOther" type="string">
            <column name="diabetes_other" length="45" />
        </property>
        <property name="firstName" type="string">
            <column name="first_name" length="100" not-null="true" />
        </property>
        <property name="lastName" type="string">
            <column name="last_name" length="100" />
        </property>        
        <property name="userName" type="string">
            <column name="user_name" length="45" not-null="true" />
        </property>
        <property name="password" type="string">
            <column name="password" length="45" not-null="true" />
        </property>
        <property name="dateCreated" type="timestamp">
            <column name="date_created" length="19" />
        </property>
        <property name="lastUpdated" type="timestamp">
            <column name="last_updated" length="19" not-null="true">
                <comment>Stores the basic information of the patient</comment>
            </column>
        </property>
        <set name="illnesses" table="illness" inverse="true" lazy="true" fetch="select">
            <key>
                <column name="patient_idpatient" not-null="true" />
            </key>
            <one-to-many class="beans.Illness" />
        </set>
        <set name="reminders" table="reminder" inverse="true" lazy="true" fetch="select">
            <key>
                <column name="patient_idpatient" not-null="true" />
            </key>
            <one-to-many class="beans.Reminder" />
        </set>
    </class>
</hibernate-mapping>

回答1:

Your json converter tries to serialize the whole entity, which contains the list of all patients speaking each language. From what i understood, the list of patient in the json is not expected. So you have three options (ordered in which i would consider them) :

  • Remove the mapping to patients in Language entity. Do you need to get acces s to patients from the language entity ? If not remove this mapping.
  • Create a Language DTO where you transfer your data before exiting the tx layer. This way whoever calls the service will never get a LazyInitException. No surprise : DTO fields are always set eagerly.
  • Configure your json converter to not serialize the patient fields. You've not said which json lib you're using. Some of them give you an annotation to ignore some fields (@JsonIgnore for Jackson for example), other requires java configuration.

To apply the first solution, update those files this way :

Language.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Sep 14, 2016 4:33:23 PM by Hibernate Tools 4.3.1 -->
<hibernate-mapping>
    <class name="beans.Language" table="language" catalog="myglukose" optimistic-lock="version">
        <id name="idlanguage" type="java.lang.Integer">
            <column name="idlanguage" />
            <generator class="identity" />
        </id>
        <property name="language" type="string">
            <column name="language" length="45" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

Language.java

public class Language  implements java.io.Serializable {
    private Integer idlanguage;
    private String language;

    protected Language() {
    }


    public Language(String language) {
        this.language = language;
    }

    public Integer getIdlanguage() {
        return this.idlanguage;
    }

    protected void setIdlanguage(Integer idlanguage) {
        this.idlanguage = idlanguage;
    }
    public String getLanguage() {
        return this.language;
    }

    public void setLanguage(String language) {
        this.language = language;
    }
}

I've updated the no-arg constructor and setId method to protected. You can even update them to private : only hibernate should ever use them (and it can use private fields / methods).



回答2:

When you try to access a lazy field you need to do that before the session of hibernate is closed.

When you exit from the context of the session is not possible for hibernate to access the database if needed, so a LazyInitializationException is thrown.

From javadoc:

Indicates access to unfetched data outside of a session context. For example, when an uninitialized proxy or collection is accessed after the session was closed.



回答3:

From current explanation I am not able to see you are doing like : language.getPatients();

But if you are writing HQL query to access all patients form Language Entity then I think you should use join . As i can see the exception if related to LazyInitializationException in beans.Language.patients.

so i will suggest below code ...Check if it usefull to you or not..

public List<Language> getAllLanguages(Session session) {
        List<Language> languages=(List<Language>)session.createQuery("from Language as l JOIN l.patients").list();
        return languages;
}


标签： java mysql hibernate rest
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