Question

这基本上是一个后续问题或重新发布，因为问题How to use enums with JPA似乎已经以专有方式解决了。这是2012年 JPA 基本相同的问题，这里使用 EclipseLink 2.3.2 。

问题是如何将Java枚举映射到具有不同名称的数据库字符串。有一个包含VARCHAR值'M'，'C'，'N'和'F'的数据库列。它们很神秘，混合了英语和德语。为了改进业务层，我想将Java枚举映射到上面的DB字符串：

public enum TradingSector
{
    EMPLOYEE( "M" ), // Mitarbeiter
    CUSTOMER( "C" ),
    NOSTRO( "N" ),
    FUND( "F" );

// this works:
//    M( "M" ),
//    C( "C" ),
//    N( "N" ),
//    F( "F" );

    private final String ch;

    private TradingSector( String ch )
    {
        this.ch = ch;
    }

    @Override
    public String toString()
    {
        return this.ch;
    }
}

这是实体：

@Entity
@Table( name = "TRADES" )
@Inheritance( strategy = InheritanceType.SINGLE_TABLE )
@DiscriminatorColumn( name = "NOSTRO_FLAG", discriminatorType = DiscriminatorType.STRING, length = 1 )
public class Trade implements Serializable
{
    @Enumerated( EnumType.STRING )
    @Column( name = "NOSTRO_FLAG", insertable = false, updatable = false )
    private TradingSector discriminator;

    ...
}

这是一种特殊的，将枚举映射到已经是继承的鉴别器。然而，这应该有效，因为名为DB字符串的枚举显示。

TRADES表是目前整个上下文中最单一的表，并且将实体拆分为子类是非常可取的。

我原本希望简单地覆盖toString从我阅读的内容开始工作，但这导致：

Caused by: Exception [EclipseLink-116] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: No conversion value provided for the value [M] in field [TRADES.TRADING_SECTOR].
Mapping: org.eclipse.persistence.mappings.DirectToFieldMapping[discriminator-->TRADES.TRADING_SECTOR]
Descriptor: RelationalDescriptor(com.company.project.model.Trade --> [DatabaseTable(TRADES)])
    at org.eclipse.persistence.exceptions.DescriptorException.noFieldValueConversionToAttributeValueProvided(DescriptorException.java:1052)
    at org.eclipse.persistence.mappings.converters.ObjectTypeConverter.convertDataValueToObjectValue(ObjectTypeConverter.java:140)
    at org.eclipse.persistence.mappings.converters.EnumTypeConverter.convertDataValueToObjectValue(EnumTypeConverter.java:137)
    at org.eclipse.persistence.mappings.foundation.AbstractDirectMapping.getAttributeValue(AbstractDirectMapping.java:699)
    at org.eclipse.persistence.mappings.foundation.AbstractDirectMapping.valueFromRow(AbstractDirectMapping.java:1299)
    at org.eclipse.persistence.mappings.DatabaseMapping.readFromRowIntoObject(DatabaseMapping.java:1326)

这是http://wiki.eclipse.org/EclipseLink_Exception_Error_Reference_%28ELUG%29上的EclipseLink错误文档所说的内容：

 ECLIPSELINK-00116: No conversion value provided for the value [{0}] in field [{1}].
    Cause: The attribute conversion value for the fieldValue was not given in the object type mapping. 
    Action: Verify the field value, and provide a corresponding attribute value in the mapping.

啊，是的。： - /

问： 非专有（JPA 2）解决这个问题的方法是什么（如果可行的话，不会进入黑客攻击范围太远）？

PS：无法更改数据库值。

Answer 1

该死的，我在这里错过了Pascal Thivent的伟大的答案：https://stackoverflow.com/a/2751896/396732

这是最终的解决方案：

枚举：

public enum TradingSector
{
    EMPLOYEE( "M" ),
    CUSTOMER( "C" ),
    NOSTRO( "N" ),
    FUND( "F" );

    private final String ch;

    private TradingSector( String ch )
    {
        this.ch = ch;
    }

    public String getCharacter()
    {
        return this.ch;
    }

    public static TradingSector translate( String ch )
    {
        for ( TradingSector ts : TradingSector.values() )
        {
            if ( ch.equals( ts.getCharacter() ) )
            {
                return ts;
            }
        }

        return null;
    }
}

实体：

@Entity
@Table( name = "TRADES" )
@Inheritance( strategy = InheritanceType.SINGLE_TABLE )
@DiscriminatorColumn( name = "NOSTRO_FLAG", discriminatorType = DiscriminatorType.STRING, length = 1 )
public abstract class Trade implements Serializable
{
    @Column( name = "NOSTRO_FLAG", insertable = false, updatable = false )
    protected String discriminator;

    @Id
    @Column( name = "TRADE_ID" )
    protected Long id;

    ...

    protected Trade()
    {
    }

    public String getDiscriminator()
    {
        return this.discriminator;
    }

    public TradingSector getTradingSector()
    {
        return TradingSector.translate( this.discriminator );
    }

    ...
}

在某种程度上仍然有用。

将名为EMPLOYEE的枚举映射到VARCHAR鉴别器值'M'

1 个答案: