Java Hibernate Annotation error java.lang.String

Question

I'm currently trying to setup hibernate for a Database, and I ran into this problem, which I've been trying to fix for like 4 hours.

The error:

Apr 27, 2021 8:22:26 AM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {5.4.0.Final}
Apr 27, 2021 8:22:26 AM org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
Apr 27, 2021 8:22:26 AM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.1.0.Final}
Apr 27, 2021 8:22:26 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
Apr 27, 2021 8:22:26 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [com.microsoft.sqlserver.jdbc.SQLServerDriver] at URL [jdbc:sqlserver://localhost:1434;DatabaseName=Chatbot]
Apr 27, 2021 8:22:26 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=sa}
Apr 27, 2021 8:22:26 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Apr 27, 2021 8:22:26 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
Apr 27, 2021 8:22:26 AM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.SQLServerDialect
org.hibernate.AnnotationException: @OneToOne or @ManyToOne on backend.classes.Result.answer references an unknown entity: java.lang.String
    at org.hibernate.cfg.ToOneFkSecondPass.doSecondPass(ToOneFkSecondPass.java:97)
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processEndOfQueue(InFlightMetadataCollectorImpl.java:1815)
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processFkSecondPassesInOrder(InFlightMetadataCollectorImpl.java:1759)
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1646)
    at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:287)
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:903)
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:934)
    at org.hibernate.jpa.HibernatePersistenceProvider.createEntityManagerFactory(HibernatePersistenceProvider.java:56)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:79)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:54)
    at backend.classes.DBConnector.setUp(DBConnector.java:28)
    at backend.classes.DBConnector.run(DBConnector.java:18)
    at backend.classes.DBConnector.main(DBConnector.java:13)

My Dataclass:

package backend.classes;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name = "dbo.AntwortUndTag")
public class Result {
    int id;
    String answer;
    String tag;
    int tagUpvotes;
    int tagDownvotes;
    int tagUsages;

    @Id
    @Column(name = "antwortUndTagID")
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "antwort")
    public String getAnswer() {
        return answer;
    }

    public void setAnswer(String answer) {
        this.answer = answer;
    }

    @OneToOne(cascade = CascadeType.ALL)
    public String getTag() {
        return tag;
    }

    public void setTag(String tag) {
        this.tag = tag;
    }

    
    public int getTagUpvotes() {
        return tagUpvotes;
    }

    public void setTagUpvotes(int tagUpvotes) {
        this.tagUpvotes = tagUpvotes;
    }

    public int getTagDownvotes() {
        return tagDownvotes;
    }

    public void setTagDownvotes(int tagDownvotes) {
        this.tagDownvotes = tagDownvotes;
    }

    @Column(name = "anzahlTagVerwendung")
    public int getTagUsages() {
        return tagUsages;
    }

    public void setTagUsages(int tagUsages) {
        this.tagUsages = tagUsages;
    }

    public Result(int id, String answer, String tag, int tagUpvotes, int tagDownvotes, int tagUsages) {
        super();
        this.id = id;
        this.answer = answer;
        this.tag = tag;
        this.tagUpvotes = tagUpvotes;
        this.tagDownvotes = tagDownvotes;
        this.tagUsages = tagUsages;
    }

    public Result() {

    }

    @Override
    public String toString() {
        return "Result [id=" + id + ", answer=" + answer + ", tag=" + tag + ", tagUpvotes=" + tagUpvotes
                + ", tagDownvotes=" + tagDownvotes + ", tagUsages=" + tagUsages + "]";
    }
}

My persistence.xml:

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
    version="2.0">

    <persistence-unit name="chatbot">
        <description>
            Persistence Unit for the Chatbot
        </description>


        <class>java.lang.String</class>
        <class>backend.classes.Result</class>
        
        <exclude-unlisted-classes>false</exclude-unlisted-classes>

        <properties>
            <property name="javax.persistence.jdbc.url" value="jdbc:sqlserver://localhost:1434;DatabaseName=Chatbot" />
            <property name="javax.persistence.jdbc.user" value="****" />
            <property name="javax.persistence.jdbc.password" value="****" />
            <property name="javax.persistence.jdbc.driver" value="com.microsoft.sqlserver.jdbc.SQLServerDriver" />

            <property name="hibernate.dialect" value="org.hibernate.dialect.SQLServerDialect" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.hbm2ddl.auto" value="create" />
        </properties>

    </persistence-unit>

</persistence>

My Demo Class to test my connection:

package backend.classes;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class DBConnector {
    private EntityManagerFactory entityManagerFactory;
    
    public static void main(String[] args) {
        new DBConnector().run();
    }

    void run() {
        try {
            setUp();
            testBasicUsage();
            tearDown();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void setUp() throws Exception {
        entityManagerFactory = Persistence.createEntityManagerFactory("chatbot");
    }

    public void tearDown() throws Exception {
        entityManagerFactory.close();
    }

    public void testBasicUsage() {
        EntityManager em = entityManagerFactory.createEntityManager();
        em.getTransaction().begin();
        
        List<Result> result = em.createQuery( "from dbo.AntwortUndTag", Result.class ).getResultList();
        for ( Result r : result ) {
            System.out.println(r.toString());
        }
        
        em.getTransaction().commit();
        em.close();
    }
}

My database looks like this: Database ORM

From both foreign keys im trying to get the 'antwort' String

I have already tried adding the classes 'Result' and 'String' in the persistence.xml

for a start why do you have <class>java.lang.String</class> ? Secondly, do you have tables called tag and answer, and if so why are they not in your persistence.xml ? — Scary Wombat
– Scary Wombat, Commented Apr 27, 2021 at 7:38
@JoinColumn(name = "antwort") looks wrong as well. Check your UML diagram — Scary Wombat
– Scary Wombat, Commented Apr 27, 2021 at 7:45

Davide D'Alto · Accepted Answer · 2021-04-27 07:52:29Z

2

Associations need to be associated to other entities (or embeddables). The error is telling you what's wrong: you are trying to associate a one to one to a String in Result.answer.

What you need to do is to map all three tables as entities:

@Entity
@Table(name = "Antworten")
class Antwort {
...
}

@Entity
@Table(name = "AntwortUndTag")
class Result {
    ...
}


@Entity
@Table(name = "Tags")
class Tag {
...
}

Now you can create the association in Result:

@Entity
@Table(name = "AntwortUndTag")
class Result {

   @ManyToOne
   @JoinColumn(name="antwortID")
   Antwort answer;

   @ManyToOne
   @JoinColumn(name="tagID")
   Tag tag;
}

Note that I've used a @ManyToOne because from the diagram it seems that an answer can have multiple tags.

You can find a lot of examples on how to map associations in the Hibernate ORM documentation. In particular see Example 172. Bidirectional many-to-many with link entity. It seems that's the mapping that you need.

edited Apr 27, 2021 at 7:52

answered Apr 27, 2021 at 7:41

Davide D'Alto

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1 Comment

Marconymous Over a year ago

It worked just like you told me, now I just have some connection / login error but I should be able to fix them myself. Thank you

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