Spring JPA 创建新记录而不是更新现有记录

如何解决Spring JPA 创建新记录而不是更新现有记录

我正在使用标准的 Spring CrudRepository。尝试更新记录时，即使为主键分配了非空值，也会创建新记录。

对我做错了什么有什么建议吗？

谢谢，蒂莫西

软件版本

Spring Boot 2.4.0
数据库 postgres 9.6.17

要保存的实体

python3 mycode.py

服务层中的保存方法

@Entity
@Table(name = "dc_motor")
public class DcMotor implements Serializable,DatabaseEntity {
    private static final long serialVersionUID = 4015060163435939638L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Version
    private Integer version;
    // other fields here
    // does NOT define equals() nor hashCode()
}

日志输出

@Override
    public DcMotorRest saveMotor(DcMotorRest motorToBeSaved) throws MotorNotFoundException {
        if (motorToBeSaved.getId() != null) {

            Optional<DcMotor> motor = dcRepo.findById(motorToBeSaved.getId());

            if (!motor.isPresent())
                throw new MotorNotFoundException(
                        "DC Motor with ID [%d] not found.  Unable to update.  Use empty / null id to create a new DC Motor"
                                .formatted(motorToBeSaved.getId()));
        }

        // troubleshooting code
        DcMotor t = new DcMotor(motorToBeSaved);
        if (t.getId() == null) {
            logger.debug("ID is null in motor to be saved");
        } else {
            logger.debug("ID is [{}] in motor to be saved",t.getId());
        }
        DcMotor savedMotor = dcRepo.save(t);    // dcRepo extends CrudRepository<DcMotor,Long>

        // DcMotor savedMotor = new DcMotor(motorToBeSaved);

        return new modelmapper().map(savedMotor,DcMotorRest.class);
    }

解决方法

你需要使用

Below method will help in getting contact name when using phone number or email id
  public static String fetchContactNameFromContacts(Context context,final String phoneOrEmail) {
        String name = phoneOrEmail;
        Uri uri;
        try {
            if (ContextCompat.checkSelfPermission(context,READ_CONTACTS) == PackageManager.PERMISSION_GRANTED) {
                Log.d(TAG,"permission granted");
                String contactName = "";
                if(isValidMobile(phoneOrEmail)) {
                    Log.d(TAG,"its phone number");
                    uri = Uri.withAppendedPath(ContactsContract.PhoneLookup.CONTENT_FILTER_URI,Uri.encode(phoneOrEmail));
                }else {
                    Log.d(TAG,"its email id");
                    uri = Uri.withAppendedPath(ContactsContract.CommonDataKinds.Email.CONTENT_FILTER_URI,Uri.encode(phoneOrEmail));

                }
                String[] projection = new String[]{ContactsContract.PhoneLookup.DISPLAY_NAME};
                Cursor cursor = context.getContentResolver().query(uri,projection,null,null);

                if (cursor != null) {
                    if (cursor.moveToFirst()) {
                        contactName = cursor.getString(0);
                    }
                    cursor.close();

                    if (contactName == null) {
                        return name;
                    }
                    if (contactName.isEmpty()) {
                        return name;
                    }
                }

            }
        } catch (Exception e) {
           
        }
        return name;
    }

更新那个实例然后调用

var inDb = dcRepo.findOne(motorToBeSaved.getId());

另一种方法是使用 dcRepo.save(inDb); https://stackoverflow.com/a/62925149/14072498

是的，问题出在这里：

DcMotor t = new DcMotor(motorToBeSaved);

基本上它是你创建的一个对象，Hibernate 不知道它，所以它被认为是一个新对象。您需要先在数据库中找到该实体，更新它然后保存。