jpa map 关系映射-蒲公英云

jpa map 关系映射

jpa Map 类型的映射关系总结

参考：https://thoughts-on-java.org/map-association-java-util-map/

key 、value 都是基础类型

@Setter
@NoArgsConstructor
@ToString
@Entity
@Table(name = “company”)
public class Company {

 private Long id;
 private String name;
 private Map<String, String> addresses = new HashMap<>();
 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 public Long getId() {
     return id;
 }
 @Column(name = "name")
 public String getName() {
     return name;
 }
 /**
  * key, value 都是基础类型 
  */
 @ElementCollection
 @CollectionTable(name = "company_address", joinColumns = @JoinColumn(name = "company_id"))
 @MapKeyColumn(name = "address_no")
 @Column(name = "address")
 public Map<String, String> getAddresses() {
     return addresses;
 }

}

mysql> select * from company;
+——+———+
| id | name |
+——+———+
| 1 | Alo7 |
+——+———+
1 row in set (0.00 sec)

mysql> select * from company_address;
+——————+—————+——————+
| company_id | address | address_no |
+——————+—————+——————+
| 1 | beijing | 001 |
| 1 | shanghai | 002 |
+——————+—————+——————+
2 rows in set (0.00 sec)

key 是基础类型，value 是 Embeddable 类

@Embeddable
@Data
@ToString
@NoArgsConstructor
@AllArgsConstructor
public class Address {
```
 private String country;
 private String street;
```
}

@ToString
@Setter
@NoArgsConstructor
@Entity
@Table(name = "schooler")
public class Schooler {
    private Long id;
    private String name;
    private Map<String, Address> addressMap = new HashMap<>();
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Long getId() {
        return id;
    }
    @Column(name = "name")
    public String getName() {
        return name;
    }
    /**
     * key 是基础类型， value 是 Embeddable 类
     */
    @ElementCollection
    @CollectionTable(name = "schooler_address", joinColumns = {@JoinColumn(name = "schooler_id")})
    @MapKeyColumn(name = "address_no")
    public Map<String, Address> getAddressMap() {
        return addressMap;
    }
}
mysql> select * from scholler;
+----+---------+
| id | name    |
+----+---------+
|  1 | qinghua |
+----+---------+
1 row in set (0.00 sec)
mysql> select * from schooler_address;
+-------------+---------+--------+------------+
| schooler_id | country | street | address_no |
+-------------+---------+--------+------------+
|           1 | CH      | Nj     | 01         |
|           1 | US      | NY     | 02         |
+-------------+---------+--------+------------+

key 是基础类型，value 是 entity

@ToString
@Setter
@NoArgsConstructor
@Entity
@Table(name = “author”)
public class Author {

 private Long id;
 private String aname;
 private Map<String, Book> books = new HashMap<>();
 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 public Long getId() {
     return id;
 }
 @Column(name = "aname")
 public String getAname() {
     return aname;
 }
 @ManyToMany
 @JoinTable(name = "author_book",
         joinColumns = {@JoinColumn(name = "author_id", referencedColumnName = "id")},
         inverseJoinColumns = {@JoinColumn(name = "book_id", referencedColumnName = "id")}
 )
 @MapKeyColumn(name = "book_name")
 public Map<String, Book> getBooks() {
     return books;
 }

}

@ToString
@Setter
@NoArgsConstructor
@Entity
@Table(name = "book")
public class Book {
    private Long id;
    private String bname;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Long getId() {
        return id;
    }
    @Column(name = "bname")
    public String getBname() {
        return bname;
    }
}
mysql> select * from author_book;
+-----------+---------+-----------+
| author_id | book_id | book_name |
+-----------+---------+-----------+
|         1 |       1 | java      |
|         1 |       2 | c#        |
+-----------+---------+-----------+
2 rows in set (0.00 sec)
mysql> select * from book;
+----+-------+
| id | bname |
+----+-------+
|  1 | java  |
|  2 | c#    |
+----+-------+
2 rows in set (0.00 sec)
mysql> select * from author;
+----+-------+
| id | aname |
+----+-------+
|  1 | wang  |
+----+-------+
1 row in set (0.00 sec)