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如何通过在休眠中使用 session.get 检索数据来跳过空值

Marina 发表于 Dev
10
码头

我想从数据库中检索一些数据，但有两个错误，NullPointerException 和“无法定位持久器”。我的数据库中有空值，如何跳过？它不应该使用我在 session.get 中提供的特定主键检索元组吗？然后元组存在于我的数据库中，为什么它告诉我它不是持久的？谢谢。

Parliamentary class

@Entity
@Table(name = "parlamentari")
@IdClass(Parlamentare.class)
public class Parlamentare implements Serializable{

@Id
@GeneratedValue(strategy= GenerationType.AUTO)
@Column(name = "nome")
 String nome;
@Id
@Column(name = "partito")
 String partito;
@Id
@Column(name = "circoscrizione")
 String circoscrizione;
 Date data_nascita; 
 String luogo; 
 String titolo_studi; 
 String[] mandati; 
 String[] commissioni;
 //DateRange[] periodo_carica;
 
 @ManyToMany(mappedBy = "parlamentare",fetch=FetchType.EAGER)
private List<Range2<LocalDate>> periodo_carica = new ArrayList<Range2<LocalDate>>();
 
 public Parlamentare() {
    
        this.nome = "";
        this.partito = "";
        this.circoscrizione = "";  
        this.data_nascita = null;
        this.luogo = null;
        this.titolo_studi = "";
        this.mandati = null;
        this.commissioni = null; 
        this.periodo_carica = null;
 }
 
public Parlamentare(String nome, String partito, String circoscrizione) {
    super();
    this.nome = nome;
    this.partito = partito;
    this.circoscrizione = circoscrizione;
}



public Parlamentare(String nome, String partito, String circoscrizione, Date data_nascita, String luogo,
        String titolo_studi, String[] mandati, String[] commissioni, List<Range2<LocalDate>> periodo_carica) {
    super();
    this.nome = nome;
    this.partito = partito;
    this.circoscrizione = circoscrizione;
    this.data_nascita = data_nascita;
    this.luogo = luogo;
    this.titolo_studi = titolo_studi;
    this.mandati = mandati;
    this.commissioni = commissioni;
    this.periodo_carica = periodo_carica;
}

....

}       
}

Range2 类与 Vlad Mihalcea 的 Range 类相同，但增加了：

@ManyToMany
private Parlamentare parlamentare;


public Parlamentare getParlamentare() {
    return parlamentare;
}


public void setParlamentare(Parlamentare parlamentare) {
    this.parlamentare = parlamentare;
}

hibernate.cfg.xml 文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
    <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
    <property name="hibernate.connection.url">jdbc:postgresql://localhost/Parlamento</property>
    <property name="hibernate.connection.username">postgres</property>
    <property name="hibernate.connection.password"></property>
    <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>
    <property name="hbm2ddl.auto">update</property>
    <property name="show_sql">true</property>
</session-factory>
</hibernate-configuration>

应用程序.java

public class App 
{
private static ServiceRegistry serviceregistry;
private static SessionFactory sf;
public static SessionFactory getSessionFactory() {
    if (sf == null) {
        StandardServiceRegistry standardRegistry = new 
 StandardServiceRegistryBuilder().configure().build();
        Metadata metadata = new MetadataSources(standardRegistry).getMetadataBuilder().build();
        sf = metadata.getSessionFactoryBuilder().build();
    }
    return sf;
}

public static void main( String[] args )throws ParseException, NullPointerException{

Parlamentare parlamentare = new Parlamentare();

Configuration con  = new 
Configuration().configure().addAnnotatedClass(Parlamentare.class).addAnnotatedClass(Range2.class);      
    
     //serviceregistry.applySettings(con.getProperties()).buildServiceRegistry();
    getSessionFactory();

    serviceregistry = new 
StandardServiceRegistryBuilder().applySettings(con.getProperties()).build();
    try {
 sf = con.buildSessionFactory(serviceregistry);
    } catch (NullPointerException e) {
        e.printStackTrace();
    }
    Session session = sf.openSession();
    session.beginTransaction(); 

    parlamentare = (Parlamentare) session.get(Parlamentare.class, 
            new Parlamentare("Abate Rosa Silvana","M5S", "Calabria"));
    //parlamentare.getpk("Abate Rosa Silvana","M5S", "Calabria"));

    System.out.println(parlamentare.getNome());
    System.out.println(parlamentare.getPartito());
    System.out.println(parlamentare.getCircoscrizione());
    System.out.println(parlamentare.getData_nascita());
    System.out.println(parlamentare.getLuogo());
    System.out.println(parlamentare.getTitolo_studi());
    System.out.println(parlamentare.getMandati()); 
    System.out.println(parlamentare.getCommissioni()); 
    System.out.println(parlamentare.getPeriodo_carica());

    
    List<Range2<LocalDate>> periodo_carica = new ArrayList<Range2<LocalDate>>();
    periodo_carica = parlamentare.getPeriodo_carica();
    for(Range2<LocalDate> dr : periodo_carica)
    {
        System.out.println(dr);
    }

    session.getTransaction().commit();
   // tx.commit();
    session.close();
    sf.close();
}

}

     OUTPUT:

mag 01, 2021 10:49:19 AM org.hibernate.Version logVersion
    INFO: HHH000412: Hibernate ORM core version 5.4.30.Final
     mag 01, 2021 10:49:19 AM org.hibernate.annotations.common.reflection.java.JavaReflectionManager

 <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
mag 01, 2021 10:49:20 AM 
 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
 WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
 mag 01, 2021 10:49:20 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [org.postgresql.Driver] at URL 
[jdbc:postgresql://localhost/Parlamento]
mag 01, 2021 10:49:20 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=postgres}
mag 01, 2021 10:49:20 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
mag 01, 2021 10:49:20 AM 
 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections

<init>
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
mag 01, 2021 10:49:21 AM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
mag 01, 2021 10:49:24 AM 
org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl

getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess   [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@7 a18e8d] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will 
 be committed and the Connection will be set into auto-commit mode.
mag 01, 2021 10:49:25 AM org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformInitiator

initiateService
INFO: HHH000490: Using JtaPlatform implementation: 
[org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
 mag 01, 2021 10:49:25 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
mag 01, 2021 10:49:25 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [org.postgresql.Driver] at URL 
[jdbc:postgresql://localhost/Parlamento]
mag 01, 2021 10:49:25 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=postgres}
 mag 01, 2021 10:49:25 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
mag 01, 2021 10:49:25 AM 
org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections

<init>
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
 mag 01, 2021 10:49:26 AM org.hibernate.dialect.Dialect <init>
 INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
 java.lang.NullPointerException     at 
org.hibernate.cfg.ColumnsBuilder.extractMetadata(ColumnsBuilder.java:144)   at 
org.hibernate.cfg.AnnotationBinder.processElementAnnotations(AnnotationBinder.java:1685)    at 
org.hibernate.cfg.AnnotationBinder.fillComponent(AnnotationBinder.java:2790)    at 
org.hibernate.cfg.AnnotationBinder.bindIdClass(AnnotationBinder.java:2893)  at 
org.hibernate.cfg.AnnotationBinder.mapAsIdClass(AnnotationBinder.java:1063)     at 
org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:791)     at  
org.hibernate.boot.model.source.internal.annotations.AnnotationMetadataSourceProcessorImpl.
processEntityHierarchies(AnnotationMetadataSourceProcessorImpl.java:248)    at  
org.hibernate.boot.model.process.spi.MetadataBuildingProcess$1.processEntityHierarchies
(MetadataBuildingProcess.java:239)  at 
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete
(MetadataBuildingProcess.java:282)  at 
org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build
(MetadataBuildingProcess.java:86)    
at org.hibernate.boot.internal.MetadataBuilderImpl.build 
(MetadataBuilderImpl.java:479)  at 
org.hibernate.boot.internal.MetadataBuilderImpl.build
(MetadataBuilderImpl.java:85)   at 
org.hibernate.cfg.Configuration.buildSessionFactory
(Configuration.java:689)    at 
swt.mvn.Parlamento.App.main(App.java:132)
Exception in thread "main" org.hibernate.UnknownEntityTypeException:
Unable to locate persister: 
swt.mvn.Parlamento.src.Servlet_Parlamento.Parlamentari.Parlamentare     at 
org.hibernate.metamodel.internal.MetamodelImpl.locateEntityPersister(MetamodelImpl.java:721)    at 
org.hibernate.internal.SessionImpl.locateEntityPersister(SessionImpl.java:2946)     at 
org.hibernate.internal.SessionImpl.access$1800(SessionImpl.java:193)    at 
org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.<init>(SessionImpl.java:2675)   at 
org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.<init>(SessionImpl.java:2658)   at 
org.hibernate.internal.SessionImpl.byId(SessionImpl.java:1140)  at 
org.hibernate.internal.SessionImpl.get(SessionImpl.java:983)    at 
swt.mvn.Parlamento.App.main(App.java:139)

议会文件

PK.java

范围2.java

戴维德

乍一看，有几件事似乎不正确：

1.多对多关联

You used a @ManyToMany on a single field:

@ManyToMany
private Parlamentare parlamentare;

This is not correct because you cannot have many Parlamentare if the association doesn't use a Collection. You need to change it to:

@ManyToMany
Set<Parlamentare> parlamentari;

or

@ManyToOne
Parlamentare parlamentare;

If it refers to a single parlamentare.

Check the Hibernate ORM documentation for examples of @ManyToMany associations and @ManyToOne associations.

2. @IdClass

You can use @IdClass to create composite identifiers, but you have to create a class that maps the identifier:

@Entity
@Table(name = "parlamentari")
@IdClass(ParlamentarePK.class)
public class Parlamentare implements Serializable{

@Id
@GeneratedValue(strategy= GenerationType.AUTO)
@Column(name = "nome")
 String nome;

@Id
@Column(name = "partito")
 String partito;

@Id
@Column(name = "circoscrizione")
String circoscrizione;
 ...
}

public class ParlamentarePK implements Serializable {

    String nome;

    String partito;

    String circoscrizione;

   ...// getters,setters and so on
}

3. EAGER associations

@ManyToMany(mappedBy ="parlamentare",fetch=FetchType.EAGER)
private List<Range2<LocalDate>> periodo_carica = new ArrayList<Range2<LocalDate>>();

This might be correct, but it's usually discouraged to map associations as eager. It may lead to poor performance because the association will always be loaded even when you don't need it.

您可以仅在需要时通过查询或实体图急切地获取关联。

为了使它变得懒惰，您可以将映射更改为：

@ManyToMany(mappedBy ="parlamentare",fetch=FetchType.LAZY)
private List<Range2<LocalDate>> periodo_carica = new ArrayList<Range2<LocalDate>>();

4. 数组作为类型

示例：

String[] commissioni;

Hibernate ORM 将这些值保存为一个二进制字节数组。我不确定这是否是你想要的。这篇关于映射数组的文章解释了所有选项。

本文收集自互联网，转载请注明来源。

如有侵权，请联系 [email protected] 删除。

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