如何使用 JPA 2.1 转换连接的元素集合？

Question

我有 3 个表 user、user_team 和 team ...

user
--------
id (number)
name (varchar)

team
--------
name (varchar)

user_team
--------
user_id (number) FK -> user.id
team_name (varchar) FK -> team.name

我想加载 User 实体，以便将团队转换为正确的类型。

@Entity
public class User implements Serializable {

    @Id
    @GeneratedValue( strategy = IDENTITY )
    private Long id;

    @Column( name = "name" )
    private String name;

    @ElementCollection
    @JoinTable( name = "user_team", 
            joinColumns = @JoinColumn( name = "user_id" ) )
    @Column( name = "team_name" )
    @Convert( converter = TeamToStringConverter.class )
    private Set<Team> teams;
}

public enum Team { NOTEAM, GEEKS, FREAKS, etc ... }

@Converter
public class TeamToStringConverter implements AttributeConverter<Team, String> {

    @Override
    public String convertToDatabaseColumn( Team value ) {
        return value == null ? NOTEAM.name() : value.name();
    }
    @Override
    public TEAM convertToEntityAttribute( String value ) {
        return Team.from( value );
    }
}

我认为问题在于它使用 TeamToStringConverter 来转换 user_team.user_id 字段而不是 user_team.team_name 字段（在 @Column 注释中指定）并且结果是异常的：

sql.SqlUtils - Attempted to convert SQLException to SQLException. Leaving it alone. [SQLState: null; errorCode: 0]
com.microsoft.sqlserver.jdbc.SQLServerException: An error occurred while converting the nvarchar value to JDBC data type INTEGER.
at com.microsoft.sqlserver.jdbc.DDC.convertStreamToObject(DDC.java:475)
at com.microsoft.sqlserver.jdbc.ServerDTVImpl.getValue(dtv.java:2536)
...
Caused by: java.lang.NumberFormatException: For input string: "NOTEAM"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
...

Answer 1

将映射更改为

@ElementCollection
@CollectionTable( name = "user_team", 
        joinColumns = @JoinColumn( name = "user_id" ) )
@Column( name = "team_name" )
@Enumerated(EnumType.STRING)
@Convert( converter = TeamToStringConverter.class )
private Set<Team> teams;

应该使用

@CollectionTable 而不是 @JoinTable，并且 @Enumerated(EnumType.STRING) 告诉 JPA 枚举值在数据库中存储为 String 而不是 Integer是默认值（枚举常量的索引）。

请注意，table team 在此设置中对 JPA 没有任何意义，因为它未映射到任何内容。

Answer 2

在低于 4.3.9 的 Hibernate 版本中，@Convert 注释不适用于集合字段。

见https://hibernate.atlassian.net/browse/HHH-9495

对于 Hibernate 较低的 4.3.9 使用 autoApply 属性:

@Converter(autoApply = true)
public class TeamToStringConverter implements AttributeConverter<Team, String> {...}

对于 Hibernate 更高版本 4.3.9 使用：

@ElementCollection
@CollectionTable( name = "user_team", joinColumns = @JoinColumn( name = "user_id" ) )
@Column( name = "team_name" )
@Convert( converter = TeamToStringConverter.class )
private Set<Team> teams;

如何使用 JPA 2.1 转换连接的元素集合？

How to convert joined element collection with JPA 2.1?

java

entity-framework

jpa