How to beautifully update a JPA entity in Spring Data

Question

So I have looked at various tutorials about JPA with Spring Data and this has been done different on many occasions and I am no quite sure what the correct approach is   Assume there is the follwing entity   package stackoverflowTest dao   import javax persistence      Entity  Table name    customers   public class Customer     Id  GeneratedValue strategy   GenerationType AUTO   Column name    id   private long id    Column name    name   private String name   public Customer String name        this name   name     public Customer        public long getId         return id     public String getName         return name     public void setName String name        this name   name        We also have a DTO which is retrieved in the service layer and then handed to the controller client side   package stackoverflowTest dto   public class CustomerDto    private long id  private String name   public CustomerDto long id  String name        this id   id      this name   name     public long getId         return id     public void setId long id        this id   id     public String getName         return name     public void setName String name        this name   name        So now assume the Customer wants to change his name in the webui - then there will be some controller action  where there will be the updated DTO with the old ID and the new name   Now I have to save this updated DTO to the database   Unluckily currently there is no way to update an existing customer  except than deleting the entry in the DB and creating a new Cusomter with a new auto-generated id   However as this is not feasible  especially considering such an entity could have hundreds of relations potentially  - so there come 2 straight forward solutions to my mind    make a setter for the id in the Customer class - and thus allow setting of the id and then save the Customer object via the corresponding repository    or   add the id field to the constructor and whenever you want to update a customer you always create a new object with the old id  but the new values for the other fields  in this case only the name    So my question is wether there is a general rule how to do this  Any maybe what the drawbacks of the 2 methods I explained are

User · Answer

I have encountered this issue   Luckily  I determine 2 ways and understand some things but the rest is not clear   Hope someone discuss or support if you know    Use RepositoryExtendJPA save entity   Example   List lt Person gt  person   this PersonRepository findById 0  person setName  Neo    This PersonReository save person   this block code updated new name for record which has id   0  Use  Transactional from javax or spring framework   Let put  Transactional upon your class or specified function  both are ok   I read at somewhere that this annotation do a  commit  action at the end your function flow  So  every things you modified at entity would be updated to database

User · Answer

If you need to work with DTOs rather than entities directly then you should retrieve the existing Customer instance and map the updated fields from the DTO to that   Customer entity     load from DB   map fields from DTO to entity

User · Answer

This is more  an object initialzation question more than a jpa question  both methods work and you can have both of them at the same time   usually if the data member value is ready before the instantiation you use the constructor parameters  if this value could be updated after the instantiation you should have a setter

User · Answer

In Spring Data you simply define an update query if you have the ID     Repository   public interface CustomerRepository extends JpaRepository lt Customer   Long gt           Query  update Customer c set c name    name WHERE c id    customerId        void setCustomerName  Param  customerId   Long id   Param  name   String name          Some solutions claim to use Spring data and do JPA oldschool  even in a manner with lost updates  instead

User · Answer

Simple JPA update      Customer customer   em find id  Customer class     Consider em as JPA EntityManager customer setName customerDto getName   em merge customer

User · Answer

Even better then  Tanjim Rahman answer you can using Spring Data JPA use the method T getOne ID id    Customer customerToUpdate   customerRepository getOne id   customerToUpdate setName customerDto getName   customerRepository save customerToUpdate     Is s better because getOne ID id  gets you only a reference  proxy  object and does not fetch it from the DB  On this reference you can set what you want and on save   it will do just an SQL UPDATE statement like you expect it  In comparsion when you call find   like in  Tanjim Rahmans answer spring data JPA will do an SQL SELECT to physically fetch the entity from the DB  which you dont need  when you are just updating

User · Answer

So now assume the Customer wants to change his name in the webui -   then there will be some controller action  where there will be the   updated DTO with the old ID and the new name    Normally  you have the following workflow    User requests his data from server and obtains them in UI  User corrects his data and sends it back to server with already present ID  On server you obtain DTO with updated data by user  find it in DB by ID  otherwise throw exception  and transform DTO -  Entity with all given data  foreign keys  etc    Then you just merge it  or if using Spring Data invoke save    which in turn will merge it  see this thread     P S  This operation will inevitably issue 2 queries  select and update  Again  2 queries  even if you wanna update a single field  However  if you utilize Hibernate s proprietary  DynamicUpdate annotation on top of entity class  it will help you not to include into update statement all the fields  but only those that actually changed   P S  If you do not wanna pay for first select statement and prefer to use Spring Data s  Modifying query  be prepared to lose L2C cache region related to modifiable entity  even worse situation with native update queries  see this thread  and also of course be prepared to write those queries manually  test them and support them in the future

[java] How to beautifully update a JPA entity in Spring Data?

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