如何正确使用JPA/Hibernate？

Question

我试图更好地理解JPA/Hibernate和SQL服务器的注释。

我创建了一个简单的项目：一个名为“Articles”的抽象类。有两个类继承了它：Ramette添加了权重，Pen添加了颜色。下面的代码无效，我无法更正错误。你有什么想法吗？非常感谢。

package fr.eni.hibernate.entities;
 
import java.io.Serializable;
 
import javax.persistence.Column;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.Table;
 
@Entity
@Table(name = "Articles")
@Inheritance( strategy = InheritanceType.SINGLE_TABLE )
@DiscriminatorColumn( name="type", discriminatorType = DiscriminatorType.STRING)
public abstract class Articles implements Serializable {
 
    private static final long serialVersionUID = 1L;
 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "idarticle")
    private Integer idarticle;
    @Column(name = "reference")
    private String reference;
    @Column(name = "marque")
    private String marque ;
    @Column(name = "designation")
    private String designation;
    @Column(name = "prixUnitaire")
    private float prixUnitaire ;
    @Column(name = "qteStock")
    private int qteStock ;
 
    public Articles() {
    }
 
 
 
    public Integer getIdArticle() {
        return idarticle;
    }
 
    public String getReference() {
        return reference;
    }
 
    public void setReference(String reference) {
        this.reference = reference;
    }
 
    public String getMarque() {
        return marque;
    }
 
    public void setMarque(String marque) {
        this.marque = marque;
    }
 
    public String getDesignation() {
        return designation;
    }
 
    public void setDesignation(String designation) {
        this.designation = designation;
    }
 
    public float getPrixUnitaire() {
        return prixUnitaire;
    }
 
    public void setPrixUnitaire(float prixUnitaire) {
        this.prixUnitaire = prixUnitaire;
    }
 
    public int getQteStock() {
        return qteStock;
    }
 
    public void setQteStock(int qteStock) {
        this.qteStock = qteStock;
    }
 
    @Override
    public String toString() {
        return "Article [idArticle=" + idarticle + ", reference=" + reference + ", marque=" + marque + ", designation="
                + designation + ", prixUnitaire=" + prixUnitaire + ", qteStock=" + qteStock + "]";
    }
 
}



package fr.eni.hibernate.entities;
 
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
 
@Entity
@DiscriminatorValue("Ramette")
public class Ramette extends Articles {
 
 
    private static final long serialVersionUID = 1L;
    private int grammage;
 
    public Ramette() {
 
    }
 
 
 
    @Column(name = "grammage")
    public int getGrammage() {
        return grammage;
    }
 
    public void setGrammage(int grammage) {
        this.grammage = grammage;
    }
 
    @Override
    public String toString() {
        return super.toString() + " Ramette [grammage=" + grammage + "]";
    }
 
}


package fr.eni.hibernate.entities;
 
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
 
@Entity
@DiscriminatorValue("Stylo")
public class Stylo extends Articles {
 
 
    private static final long serialVersionUID = 1L;
    private String couleur;
 
    public Stylo() {
 
    }
 
 
 
    @Column(name = "couleur")
    public String getCouleur() {
        return couleur;
    }
 
    public void setCouleur(String couleur) {
        this.couleur = couleur;
    }
 
    @Override
    public String toString() {
        return super.toString() + " Stylo [couleur=" + couleur + "]";
    }
 
}



package fr.eni.hibernate.entities;
 
import java.util.List;
 
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.TypedQuery;
 
public class Main {
 
    public static void main(String[] args) throws Exception {
 
        EntityManagerFactory entityManagerFactory = null;
        EntityManager entityManager = null;
        try {
            entityManagerFactory = Persistence.createEntityManagerFactory("WebStore");
            entityManager = entityManagerFactory.createEntityManager();
 
            TypedQuery<Articles> query = entityManager.createQuery("from Articles", Articles.class);
            List<Articles> art = query.getResultList();
            for (Articles article : art) {
                System.out.println(art.getClass().getName());
                System.out.println("\t" + article);
            }
 
        } finally {
            if (entityManager != null)
                entityManager.close();
            if (entityManagerFactory != null)
                entityManagerFactory.close();
        }
    }
}



<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns<img src="images/smilies/icon_mad.gif" border="0" alt="" title=":x" class="inlineimg" />si="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="WebStore">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
 
        <class>fr.eni.hibernate.entities.Articles</class>
                <class>fr.eni.hibernate.entities.Stylo</class>
                <class>fr.eni.hibernate.entities.Ramette</class>
 
 
        <properties>
            <property name="javax.persistence.jdbc.driver"
                value="com.microsoft.sqlserver.jdbc.SQLServerDriver" />
            <property name="javax.persistence.jdbc.url"
                value="jdbc:sqlserver://localhost;database=PAPETERIE_TEST" />
            <property name="javax.persistence.jdbc.user" value="xx" />
            <property name="javax.persistence.jdbc.password" value="x" />
 
            <property name="hibernate.dialect"
                value="org.hibernate.dialect.SQLServerDialect" />
            <property name="hibernate.format_sql" value="false" />
        </properties>
    </persistence-unit>
 
</persistence>


CREATE TABLE Articles
(
    idarticle INT IDENTITY(1,1),
    reference varchar(10) NOT NULL,
    marque nvarchar(200) NOT NULL,
    designation nvarchar(250) NOT NULL,
    prixUnitaire float NOT NULL,
    qteStock int NOT NULL,
    grammage int NULL,
    couleur nvarchar(50) NULL,
    type nchar(10) NOT NULL,
 
    CONSTRAINT PK_Articles PRIMARY KEY (idarticle)
)
 
INSERT INTO Articles (reference, marque, designation, prixUnitaire, qteStock, grammage, couleur, type) 
VALUES ('Bic', 'BBOrange', 'Bic bille Orange', 1.2, 20, 0, 'Bleu', 'Stylo'),
       ('Bic', 'BBOrange', 'Bic bille Orange', 1.2, 20, 0,'noir', 'Stylo'),
       ('Clairef', 'CRA4S', 'Ramette A4 Sup', 9, 20, 80, null, 'Ramette');

Answer 1

这没有多大意义。只有当表中的鉴别器在实体模型中没有匹配项时，才会引发此异常。也许您在表中有尾随空格？