使用Hibernate加入JOIN的问题

Question

I'm beginner in Hibernate in JAVA and do not know how to solve this problem

I have two tables: Usuario and Certificado, and i want to create a relationship and theirs.

Class Certificado:

@Entity
@Table(name = "Certificado",
       uniqueConstraints = { @UniqueConstraint( columnNames = { "identifierUnique", "handleUser" } ) } )
public class Certificado {
    @Id
    @GenericGenerator(name="generator", strategy="increment")
    @GeneratedValue(generator="generator")
    private int handle;
    @Column(length = 255)
    @Column
    private int handleUser;

    @ManyToOne
    @JoinColumn(name="handle_user", referencedColumnName="handle")
    private Usuario usuario;
}

Class Usuario:

@Entity
@Table(name = "Usuario")
public class Usuario {
    @Id
    @GenericGenerator(name="generator", strategy="increment")
    @GeneratedValue(generator="generator")
    private int handle;
    @Column(length = 255, unique = true)
    private String email;   
    @Column(length = 20)
    private String password;    
    @OneToMany(mappedBy="usuario", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Set<Certificado> certificados;

        ...
}

When I Execute a SQL function:

public static List<Object[]> loadCertificado30DaysBeforeExperation() throws Exception{      
        Session.begin();
        try {
            try {
                String select = "SELECT c FROM Certificado c "
                    + "LEFT JOIN c.handleUser AS user";
                return Session.list(select);
            } catch (Exception e) {
                throw e;
            }
        } finally {
            Session.commit();
        }
    }

Error:

   java.lang.NullPointerException

StackTrace:

java.lang.NullPointerException
    at org.hibernate.hql.internal.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:393)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3645)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3431)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:3309)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:706)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:562)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:299)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:247)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:249)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:184)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:137)
    at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:105)
    at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:80)
    at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:168)
    at org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:221)
    at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:199)
    at org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1778)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.hibernate.context.internal.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:352)
    at com.sun.proxy.$Proxy15.createQuery(Unknown Source)
    at br.com.persistence.Session.list(Session.java:96)
    at br.com.utils.ServletUtils.loadCertificado30DaysBeforeExperation(ServletUtils.java:134)
    at br.com.monitoramento.MonitorThread.run(MonitorThread.java:25)

Answer 1

Hibernate's HQL does not support intervals ( and generally has extremely poor date maths support ).

You'll need to use native SQL, or express the query without interval by doing the date calculations locally on the Java side.

Or you can register a user-defined SQL function and create a PostgreSQL function that does the date maths you want.

See:

• Performing Date/Time Math In HQL?
• how to use date() in hibernate criteria
• Hibernate Criteria: NOW() < date + 1 day
• Date operations in HQL

and many more.

Answer 2

Have you tried removing the '' from '30' -> interval 30 days. Or escape the '30' -> \\'30\\'.