如何在jpa single_table继承中更新父类？

Question

我有一个类ContactDTO的JPA继承，UserDTO使用 Single_Table 策略进行扩展：

package ch.ffhs.cryptomess.server.dto;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.DiscriminatorValue;
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.ManyToMany;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;
import javax.persistence.Version;

import org.springframework.transaction.annotation.Transactional;

@Transactional
@Entity(name = "ch.ffhs.cryptomess.server.dto.ContactDTO")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "discriminator", discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue(value = "ContactDTO")
@Table(name = "user", uniqueConstraints = @UniqueConstraint(columnNames = {
        "username", "discriminator" }))
public class ContactDTO implements Serializable {

    private static final long serialVersionUID = 7706720499337697645L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY, generator = "user_id_seq")
    @SequenceGenerator(name = "user_id_seq", allocationSize = 1, initialValue = 10)
    @Column(name = "id")
    protected Long id;

    @Version
    protected Long version;

    @Column(name = "public_key", length = 255)
    protected String publicKey;

    @Id
    @Column(length = 50, updatable = false)
    protected String username;

    @ManyToMany(mappedBy = "contacts", targetEntity = CommunicationDTO.class)
    protected Set<CommunicationDTO> communications = new HashSet<CommunicationDTO>(
            0);

    @Override
    public boolean equals(final Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        final ContactDTO other = (ContactDTO) obj;
        if (username == null) {
            if (other.username != null)
                return false;
        } else if (!username.equals(other.username))
            return false;
        return true;
    }

    public Set<CommunicationDTO> getCommunications() {
        return communications;
    }

    public Long getId() {
        return id;
    }

    public String getPublicKey() {
        return publicKey;
    }

    public String getUsername() {
        return username;
    }

    public Long getVersion() {
        return version;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((username == null) ? 0 : username.hashCode());
        return result;
    }

    public void setCommunications(final Set<CommunicationDTO> communications) {
        this.communications = communications;
    }

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

    public void setPublicKey(final String publicKey) {
        this.publicKey = publicKey;
    }

    public void setUsername(final String username) {
        this.username = username;
    }

    public void setVersion(final Long version) {
        this.version = version;
    }
}

和

package ch.ffhs.cryptomess.shared.dto;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;

import org.springframework.transaction.annotation.Transactional;

import ch.ffhs.cryptomess.server.dto.ContactDTO;

import com.google.gwt.view.client.ProvidesKey;

@Transactional
@Entity
@DiscriminatorValue(value = "UserDTO")
public class UserDTO extends ContactDTO implements Serializable {

    private static final long serialVersionUID = -3078472527069117428L;

    @Column(length = 80)
    protected String password;

    @Column(name = "is_account_non_expired", columnDefinition = "BIT")
    protected boolean isAccountNonExpired;

    @Column(name = "is_account_locked", columnDefinition = "BIT")
    protected boolean isAccountLocked;

    @Column(name = "is_credentials_non_expired", columnDefinition = "BIT")
    protected boolean isCredentialsNonExpired;

    @Column(name = "is_disabled", columnDefinition = "BIT")
    protected boolean isDisabled;

    /**
     * The key provider that provides the unique ID of a contact.
     */
    public static final ProvidesKey<UserDTO> KEY_PROVIDER = new ProvidesKey<UserDTO>() {

        @Override
        public Object getKey(final UserDTO item) {
            return item == null ? null : item.getId();
        }
    };

    public String getPassword() {
        return password;
    }

    public boolean isAccountLocked() {
        return isAccountLocked;
    }

    public boolean isAccountNonExpired() {
        return isAccountNonExpired;
    }

    public boolean isAccountNonLocked() {
        return !isAccountLocked;
    }

    public boolean isCredentialsNonExpired() {
        return isCredentialsNonExpired;
    }

    public boolean isDisabled() {
        return isDisabled;
    }

    public boolean isEnabled() {
        return !isDisabled;
    }

    public void setAccountLocked(final boolean isAccountLocked) {
        this.isAccountLocked = isAccountLocked;
    }

    public void setAccountNonExpired(final boolean isAccountNonExpired) {
        this.isAccountNonExpired = isAccountNonExpired;
    }

    public void setAccountNonLocked(final boolean isAccountNonLocked) {
        this.isAccountLocked = !isAccountNonLocked;
    }

    public void setCredentialsNonExpired(final boolean isCredentialsNonExpired) {
        this.isCredentialsNonExpired = isCredentialsNonExpired;
    }

    public void setDisabled(final boolean isDisabled) {
        this.isDisabled = isDisabled;
    }

    public void setEnabled(final boolean isEnabled) {
        this.isDisabled = !isEnabled;
    }

    public void setPassword(final String password) {
        this.password = password;
    }
}

如果我在UserDTO - enity上进行合并或创建，我希望在数据库中创建/更新ContactDTO - 实体。有没有办法实现这一点，而不单独处理这两个实体？

感谢您的帮助！