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NEWSGROUP テーブルに余分な行があります。それを防ぐためにエンティティまたはクエリを変更するにはどうすればよいですか?

スキーマ:

mysql> 
mysql> USE usenet;SHOW TABLES;DESCRIBE ARTICLE;DESCRIBE NEWSGROUP;
Database changed
+------------------+
| Tables_in_usenet |
+------------------+
| ARTICLE          |
| NEWSGROUP        |
+------------------+
2 rows in set (0.00 sec)

+---------------+------------+------+-----+---------+----------------+
| Field         | Type       | Null | Key | Default | Extra          |
+---------------+------------+------+-----+---------+----------------+
| ID            | bigint(20) | NO   | PRI | NULL    | auto_increment |
| MESSAGENUMBER | int(11)    | YES  |     | NULL    |                |
| NEWSGROUP_ID  | bigint(20) | YES  | MUL | NULL    |                |
+---------------+------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| ID        | bigint(20)   | NO   | PRI | NULL    | auto_increment |
| NEWSGROUP | varchar(255) | YES  |     | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql>

当分の間ソリューションをシンプルに保つためにデータベースへの単一接続を想定していますが、それは複雑なトピックであることがわかりますが、おそらく「正しい」条件を想定したシンプルなアプローチがあるでしょう。

Article エンティティ:

    package net.bounceme.dur.usenet.model;

    import java.io.Serializable;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.Set;
    import javax.mail.Folder;
    import javax.mail.Message;
    import javax.persistence.*;

    @Entity
    public class Article implements Serializable {

        private static final long serialVersionUID = 1L;
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;
        @Column
        private int messageNumber;
        @ManyToOne(cascade = CascadeType.PERSIST)
        private Newsgroup newsgroup;

        public Article() {
        }

        public Article(Message message, Folder folder) {
            messageNumber = message.getMessageNumber();
            newsgroup = new Newsgroup(folder); //need to ensure uniqueness
        }

        public Long getId() {
            return id;
        }

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

        @Override
        public int hashCode() {
            int hash = 0;
            hash += (id != null ? id.hashCode() : 0);
            return hash;
        }

        @Override
        public boolean equals(Object object) {
            // TODO: Warning - this method won't work in the case the id fields are not set
            if (!(object instanceof Article)) {
                return false;
            }
            Article other = (Article) object;
            if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
                return false;
            }
            return true;
        }

        @Override
        public String toString() {
            return "\nmessageNumber\t" + messageNumber;
        }

        public int getMessageNumber() {
            return messageNumber;
        }

        public void setMessageNumber(int messageNumber) {
            this.messageNumber = messageNumber;
        }
    }



And the Newsgroup entity:


package net.bounceme.dur.usenet.model;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.mail.Folder;
import javax.persistence.*;

@Entity
public class Newsgroup implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column //@Unique @UniqueConstraint interface..?
    private String newsgroup;
    @OneToMany(mappedBy = "newsgroup", cascade = CascadeType.PERSIST)
    private Set<Article> articles = new HashSet<>();

    public Newsgroup() {
    }

    public Newsgroup(Folder folder) {
        newsgroup = folder.getFullName();//if row already exists, then what?
    }

    public Long getId() {
        return id;
    }

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

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Newsgroup)) {
            return false;
        }
        Newsgroup other = (Newsgroup) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return newsgroup;
    }
}

毎回新しいニュースグループ エンティティを作成する代わりに、まず既存のニュースグループを照会するにはどうすればよいですか?

NEWSGROUP の余分な行:

mysql> 
mysql> USE usenet;SELECT * FROM ARTICLE;SELECT * FROM NEWSGROUP;
Database changed
+----+---------------+--------------+
| ID | MESSAGENUMBER | NEWSGROUP_ID |
+----+---------------+--------------+
|  1 |             4 |            1 |
|  2 |             5 |            2 |
|  3 |             6 |            3 |
|  4 |             7 |            4 |
|  5 |             8 |            5 |
|  6 |             9 |            6 |
|  7 |            10 |            7 |
|  8 |            11 |            8 |
|  9 |             4 |            9 |
| 10 |             4 |           10 |
| 11 |             5 |           11 |
| 12 |             6 |           12 |
| 13 |             7 |           13 |
| 14 |             8 |           14 |
| 15 |             9 |           15 |
| 16 |            10 |           16 |
| 17 |            11 |           17 |
| 18 |             4 |           18 |
| 19 |             5 |           19 |
| 20 |             6 |           20 |
| 21 |             7 |           21 |
| 22 |             8 |           22 |
| 23 |             9 |           23 |
| 24 |            10 |           24 |
| 25 |            11 |           25 |
+----+---------------+--------------+
25 rows in set (0.00 sec)

+----+-------------------------------+
| ID | NEWSGROUP                     |
+----+-------------------------------+
|  1 | gwene.com.androidcentral      |
|  2 | gwene.com.androidcentral      |
|  3 | gwene.com.androidcentral      |
|  4 | gwene.com.androidcentral      |
|  5 | gwene.com.androidcentral      |
|  6 | gwene.com.androidcentral      |
|  7 | gwene.com.androidcentral      |
|  8 | gwene.com.androidcentral      |
|  9 | gwene.com.blogspot.emacsworld |
| 10 | gwene.com.blogspot.googlecode |
| 11 | gwene.com.blogspot.googlecode |
| 12 | gwene.com.blogspot.googlecode |
| 13 | gwene.com.blogspot.googlecode |
| 14 | gwene.com.blogspot.googlecode |
| 15 | gwene.com.blogspot.googlecode |
| 16 | gwene.com.blogspot.googlecode |
| 17 | gwene.com.blogspot.googlecode |
| 18 | gwene.com.economist           |
| 19 | gwene.com.economist           |
| 20 | gwene.com.economist           |
| 21 | gwene.com.economist           |
| 22 | gwene.com.economist           |
| 23 | gwene.com.economist           |
| 24 | gwene.com.economist           |
| 25 | gwene.com.economist           |
+----+-------------------------------+
25 rows in set (0.00 sec)

mysql>
4

1 に答える 1

1

あなたの問題は、常にニュースグループを削除していることです...もちろん、記事を保存すると、IDがないため、新しい「冗長な」ニュースグループがデータベースに挿入されます。

ヒント（うまくいけば）：

Articles Countstructor 内 (または Article クラスの外側) を検索して、Article に追加する NewsGroup を探します。

私の問題は...その「フォルダー」が何であるかわからないので、UAのヒントを与えることができます：

Query query = entityManager.createNativeQuery("SELECT * FROM Newsgroup WHERE "dunno what you want to select here" = ?1",
            Newsgroup.class);
query.setParameter(1, "your parameter);

Newsgroup group = (Newsgroup) query.getSingleResult();

NewsGroup がnull新しい One を作成する場合は、見つけたものを追加します。

于 2012-08-03T09:35:10.073 に答える