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    Spring Data JPA Enum converter

Column 使用 NUMBER 型別，如何在 JPA 中用 Enum 做 mapping，且不使用 @Enumerated(EnumType.ORDINAL)
CREATE TABLE CHALLENGE_LOG (
  ACTION NUMBER(1) NOT NULL
);
COMMENT ON COLUMN CHALLENGE_LOG.ACTION IS '0=Send OTP, 1=Verify OTP';
1. 新增 PersistableEnum interface，要 mapping 的 Enum 需要實作此介面

public interface PersistableEnum<T> {
  T getCode();
}
2. 新增一個通用的 AbstractEnumConverter，實作 javax.persistence.AttributeConverter

import javax.persistence.AttributeConverter;

/*
 Base Enum converter for JPA
*/
public abstract class AbstractEnumConverter<T extends Enum<T> & PersistableEnum<E>, E>
    implements AttributeConverter<T, E> {

  private final Class<T> clazz;

  public AbstractEnumConverter(Class<T> clazz) {
    this.clazz = clazz;
  }

  @Override
  public E convertToDatabaseColumn(T attribute) {
    return attribute != null ? attribute.getCode() : null;
  }

  @Override
  public T convertToEntityAttribute(E dbData) {
    T[] enums = clazz.getEnumConstants();

    for (T e : enums) {
      if (e.getCode().equals(dbData)) {
        return e;
      }
    }

    throw new UnsupportedOperationException(
        String.format("%s cannot convert to %s enum value.", dbData, clazz));
  }
}
3. 新增 Enum. 實作 PersistableEnum 並新增 converter

@Getter
@AllArgsConstructor
public enum ChallengeAction implements PersistableEnum<Integer> {
  // 0=Send OTP, 1=Verify OTP
  SEND_OTP(0),
  VERIFY_OTP(1);

  private final Integer code;

  // JPA converter
  @javax.persistence.Converter(autoApply = true)
  public static class Converter extends AbstractEnumConverter<ChallengeAction, Integer> {
    public Converter() {
      super(ChallengeAction.class);
    }
  }
}
4. Entity. action 欄位使用 ChallengeAction enum

@Entity
@Data
public class ChallengeLog  {
  @Id
  @GeneratedValue(generator = "UUID")
  @GenericGenerator(name = "UUID", strategy = "org.hibernate.id.UUIDGenerator")
  @Column(name = "UUID")
  private String id;
  
  private ChallengeAction action;

}
5. 測試

Insert
ChallengeLog challengeLog = new ChallengeLog();
challengeCodeLog.setAction(ChallengeAction.SEND_OTP);
challengeCodeRepository.save(challengeCodeLog);
// -> action 欄位為 0
Query
challengeCodeRepository.findAll();
// -> 正確將 action 欄位 mapping 成 ChallengeAction enum