多語言JPA實體映射

Question

使用此示例：

CREATE TABLE IF NOT EXISTS COUNTRY (
    COUNTRY_CODE            VARCHAR(3) NOT NULL,
    DIALLING_CODE           VARCHAR(5) NOT NULL,
    CREATION_TIMESTAMP      TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    CREATED_BY              VARCHAR(20) NOT NULL,
    LAST_UPDATE_TIMESTAMP   TIMESTAMP NULL ON UPDATE CURRENT_TIMESTAMP,
    LAST_UPDATED_BY         VARCHAR(20),
    DELETION_TIMESTAMP      TIMESTAMP NULL,
    DELETED_BY              VARCHAR(20),

    PRIMARY KEY(NUMERIC_CODE),
    UNIQUE(ALPHA2_CODE),
    UNIQUE(ALPHA3_CODE),
    UNIQUE(DIALLING_CODE),
    FOREIGN KEY(CREATED_BY) REFERENCES USER(USER_NAME),
    FOREIGN KEY(LAST_UPDATED_BY) REFERENCES USER(USER_NAME),
    FOREIGN KEY (DELETED_BY) REFERENCES USER(USER_NAME)
) CHARACTER SET utf8;

CREATE TABLE IF NOT EXISTS COUNTRY_NAME (
    COUNTRY_CODE            VARCHAR(3) NOT NULL,
    LANGUAGE_CODE           VARCHAR(2) NOT NULL,
    NAME                    VARCHAR(20) NOT NULL,
    CREATION_TIMESTAMP      TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    CREATED_BY              VARCHAR(20) NOT NULL,
    LAST_UPDATE_TIMESTAMP   TIMESTAMP NULL ON UPDATE CURRENT_TIMESTAMP,
    LAST_UPDATED_BY         VARCHAR(20),

    PRIMARY KEY (COUNTRY_CODE, LANGUAGE_CODE),
    FOREIGN KEY (COUNTRY_CODE) REFERENCES COUNTRY (COUNTRY_CODE),
    FOREIGN KEY (LANGUAGE_CODE) REFERENCES LANGUAGE (ALPHA2_CODE),
    FOREIGN KEY (CREATED_BY) REFERENCES USER(USER_NAME),
    FOREIGN KEY (LAST_UPDATED_BY) REFERENCES USER(USER_NAME)
) CHARACTER SET utf8;

國家的JPA代表如下：

@XmlRootElement
@Entity
@Table(name="COUNTRY")
@Access(AccessType.FIELD)
@Cacheable
public class Country extends AbstractSoftDeleteAuditableEntity<String> implements za.co.sindi.persistence.entity.Entity<String>, Serializable {

    private static final long serialVersionUID = -4019436514961967327L;

    @Id
    @Column(name="COUNTRY_CODE", length=3, nullable=false)
    @Size(min=3, max=3)
    @Pattern(regexp="^\\d{3}$")
    private String id;

    @Column(name="DIALLING_CODE", length=5, nullable=false)
    @Pattern(regexp="^\\+[0-9]{2,5}$")
    private String diallingCode;

    @OneToMany(cascade= CascadeType.ALL, mappedBy="country")
    private List<CountryName> names;


    /* (non-Javadoc)
     * @see za.co.sindi.entity.IDBasedEntity#getId()
     */
    public String getId() {
        // TODO Auto-generated method stub
        return id;
    }

    /* (non-Javadoc)
     * @see za.co.sindi.entity.IDBasedEntity#setId(java.io.Serializable)
     */
    public void setId(String id) {
        // TODO Auto-generated method stub
        this.id = id;
    }

    /**
     * @return the diallingCode
     */
    public String getDiallingCode() {
        return diallingCode;
    }

    /**
     * @param diallingCode the diallingCode to set
     */
    public void setDiallingCode(String diallingCode) {
        this.diallingCode = diallingCode;
    }

    /**
     * @return the names
     */
    public List<CountryName> getNames() {
        return names;
    }

    /**
     * @param names the names to set
     */
    public void setNames(List<CountryName> names) {
        this.names = names;
    }
}

使用上面的模型，我將必須迭代names屬性以找到與語言代碼匹配的CountryName 。

是否有更好的方法根據語言代碼檢索Country和CountryName ？ 如果沒有，如何實現一種更簡單的方法，使我可以將帶有語言代碼的Country信息提取到實體，如下所示：

public class Country implements Serializable {
        private static final long serialVersionUID = -4019436514961967327L;

        @Id
        @Column(name="COUNTRY_CODE", length=3, nullable=false)
        @Size(min=3, max=3)
        @Pattern(regexp="^\\d{3}$")
        private String id;

        @Column(name="DIALLING_CODE", length=5, nullable=false)
        @Pattern(regexp="^\\+[0-9]{2,5}$")
        private String diallingCode;

        private String name;

        private Language language;


        //Getters and setters will be auto generated here....
}

這樣，可以實現：

Country country = countryDAO.find(countryCode);
System.out.println(country.getName());

Answer 1

正如我在評論中所說，我認為最好的解決方案是對CountryName使用單獨的查詢（和DAO），因為當您只需要為指定的countryCode一個國家名稱時，它將避免加載不必要的國家名稱。

一種選擇是使用@Transient java.util.Map字段，該字段將使用國家/地區名稱（使用countryCode作為映射鍵）加載，

@Transient
private Map<String, CountryName> countryNameMap;
...
public CountryName getName(String countryCode) {
    if (countryNameMap == null) {
        countryNameMap = loadNamesIntoMap(); // a loop with countryNameMap.put(countryName.getCountryCode(), countryName)
    }
    return countryNameMap.get(countryCode);
}

另一個有趣的選擇是實際上將java.util.Map用於Country和CountryName之間的關系

@OneToMany(mappedBy="country")
@MapKey(name="countryCode")
private Map<String, CountryName> names;

然后，您可以使用country.getNames().get(countryCode)訪問名稱。