How do I update an entity using spring-data-jpa

Question

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

User · Answer

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

User · Answer

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    lt form input type  quot hidden quot   path  quot id quot  value  quot   user id  quot   gt   Java   PostMapping  quot  update quot   public String updateUser  ModelAttribute User user        repo save user       return  quot redirect userlist quot      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

User · Answer

Identity of entities is defined by their primary keys  Since firstname and lastname are not parts of the primary key  you cannot tell JPA to treat Users with the same firstnames and lastnames as equal if they have different userIds   So  if you want to update a User identified by its firstname and lastname  you need to find that User by a query  and then change appropriate fields of the object your found  These changes will be flushed to the database automatically at the end of transaction  so that you don t need to do anything to save these changes explicitly   EDIT   Perhaps I should elaborate on overall semantics of JPA  There are two main approaches to design of persistence APIs    insert update approach  When you need to modify the database you should call methods of persistence API explicitly  you call insert to insert an object  or update to save new state of the object to the database  Unit of Work approach  In this case you have a set of objects managed by persistence library  All changes you make to these objects will be flushed to the database automatically at the end of Unit of Work  i e  at the end of the current transaction in typical case   When you need to insert new record to the database  you make the corresponding object managed  Managed objects are identified by their primary keys  so that if you make an object with predefined primary key managed  it will be associated with the database record of the same id  and state of this object will be propagated to that record automatically    JPA follows the latter approach  save   in Spring Data JPA is backed by merge   in plain JPA  therefore it makes your entity managed as described above  It means that calling save   on an object with predefined id will update the corresponding database record rather than insert a new one  and also explains why save   is not called create

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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 lt UserEntity  UserKey gt    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

User · Answer

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

User · Answer

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 lt T ID gt      Ok  let s check the save   implementation at SimpleJpaRepository lt T  ID gt     Transactional public  lt S extends T gt  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

User · Answer

public void updateLaserDataByHumanId String replacement  String humanId        List lt LaserData gt  laserDataByHumanId   laserDataRepository findByHumanId humanId       laserDataByHumanId stream                map en - gt  en setHumanId replacement                collect Collectors toList                 forEach en - gt  laserDataRepository save en

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

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