[java] How do I update an entity using spring-data-jpa?

Well the question pretty much says everything. Using JPARepository how do I update an entity?

JPARepository has only a save method, which does not tell me if it's create or update actually. For example, I insert a simple Object to the database User, which has three fields: firstname, lastname and age:

 @Entity
 public class User {

  private String firstname;
  private String lastname;
  //Setters and getters for age omitted, but they are the same as with firstname and lastname.
  private int age;

  @Column
  public String getFirstname() {
    return firstname;
  }
  public void setFirstname(String firstname) {
    this.firstname = firstname;
  }

  @Column
  public String getLastname() {
    return lastname;
  }
  public void setLastname(String lastname) {
    this.lastname = lastname;
  }

  private long userId;

  @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
  public long getUserId(){
    return this.userId;
  }

  public void setUserId(long userId){
    this.userId = userId;
  }
}

Then I simply call save(), which at this point is actually an insert into database:

 User user1 = new User();
 user1.setFirstname("john"); user1.setLastname("dew");
 user1.setAge(16);

 userService.saveUser(user1);// This call is actually using the JPARepository: userRepository.save(user);

So far so good. Now I want to update this user, say change his age. For this purpose I could use a Query, either QueryDSL or NamedQuery, whatever. But, considering I just want to use spring-data-jpa and the JPARepository, how do I tell it that instead of an insert I want to do an update?

Specifically, how do I tell spring-data-jpa that users with the same username and firstname are actually EQUAL and that the existing entity supposed to be updated? Overriding equals did not solve this problem.

Since the answer by @axtavt focuses on JPA not spring-data-jpa

To update an entity by querying then saving is not efficient because it requires two queries and possibly the query can be quite expensive since it may join other tables and load any collections that have fetchType=FetchType.EAGER

Spring-data-jpa supports update operation.
You have to define the method in Repository interface.and annotated it with @Query and @Modifying.

@Modifying
@Query("update User u set u.firstname = ?1, u.lastname = ?2 where u.id = ?3")
void setUserInfoById(String firstname, String lastname, Integer userId);

@Query is for defining custom query and @Modifying is for telling spring-data-jpa that this query is an update operation and it requires executeUpdate() not executeQuery().

You can specify other return types:
int - the number of records being updated.
boolean - true if there is a record being updated. Otherwise, false.

Note: Run this code in a Transaction.

Specifically how do I tell spring-data-jpa that users that have the same username and firstname are actually EQUAL and that it is supposed to update the entity. Overriding equals did not work.

For this particular purpose one can introduce a composite key like this:

CREATE TABLE IF NOT EXISTS `test`.`user` (
  `username` VARCHAR(45) NOT NULL,
  `firstname` VARCHAR(45) NOT NULL,
  `description` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`username`, `firstname`))

Mapping:

@Embeddable
public class UserKey implements Serializable {
    protected String username;
    protected String firstname;

    public UserKey() {}

    public UserKey(String username, String firstname) {
        this.username = username;
        this.firstname = firstname;
    }
    // equals, hashCode
}

Here is how to use it:

@Entity
public class UserEntity implements Serializable {
    @EmbeddedId
    private UserKey primaryKey;

    private String description;

    //...
}

JpaRepository would look like this:

public interface UserEntityRepository extends JpaRepository<UserEntity, UserKey>

Then, you could use the following idiom: accept DTO with user info, extract name and firstname and create UserKey, then create a UserEntity with this composite key and then invoke Spring Data save() which should sort everything out for you.

public void updateLaserDataByHumanId(String replacement, String humanId) {
    List<LaserData> laserDataByHumanId = laserDataRepository.findByHumanId(humanId);
    laserDataByHumanId.stream()
            .map(en -> en.setHumanId(replacement))
            .collect(Collectors.toList())
            .forEach(en -> laserDataRepository.save(en));
}

If your primary key is autoincrement then, you have to set the value for the primary key. for the save(); method to work as a update().else it will create a new record in db.

if you are using jsp form then use hidden filed to set primary key.

Jsp:

<form:input type="hidden" path="id" value="${user.id}"/>

Java:

@PostMapping("/update")
public String updateUser(@ModelAttribute User user) {
    repo.save(user);
    return "redirect:userlist";
}

also look at this:

@Override
  @Transactional
  public Customer save(Customer customer) {

    // Is new?
    if (customer.getId() == null) {
      em.persist(customer);
      return customer;
    } else {
      return em.merge(customer);
    }
  }

This is how I solved the problem:

User inbound = ...
User existing = userRepository.findByFirstname(inbound.getFirstname());
if(existing != null) inbound.setId(existing.getId());
userRepository.save(inbound);

Using spring-data-jpa save(), I was having same problem as @DtechNet. I mean every save() was creating new object instead of update. To solve this I had to add version field to entity and related table.

spring data save() method will help you to perform both: adding new item and updating an existed item.

Just call the save() and enjoy the life :))

As what has already mentioned by others, the save() itself contains both create and update operation.

I just want to add supplement about what behind the save() method.

Firstly, let's see the extend/implement hierarchy of the CrudRepository<T,ID>,

Ok, let's check the save() implementation at SimpleJpaRepository<T, ID>,

@Transactional
public <S extends T> S save(S entity) {

    if (entityInformation.isNew(entity)) {
        em.persist(entity);
        return entity;
    } else {
        return em.merge(entity);
    }
}

As you can see, it will check whether the ID is existed or not firstly, if the entity is already there, only update will happen by merge(entity) method and if else, a new record is inserted by persist(entity) method.

You can simply use this function with save() JPAfunction, but the object sent as parameter must contain an existing id in the database otherwise it will not work, because save() when we send an object without id, it adds directly a row in database, but if we send an object with an existing id, it changes the columns already found in the database.

public void updateUser(Userinfos u) {
    User userFromDb = userRepository.findById(u.getid());
    // crush the variables of the object found
    userFromDb.setFirstname("john"); 
    userFromDb.setLastname("dew");
    userFromDb.setAge(16);
    userRepository.save(userFromDb);
}