Spring Data JPA findOne change to Optional how to use this

Question

I m learning SpringBoot2 0 with Java8   And I followed some blog-making tutorial example   The tutorial source code is    GetMapping    id  edit   public String edit  PathVariable Long id  Model model      model addAttribute  categoryDto   categoryService findOne id      return  category edit       But this code is throwing this error      categoryService findOne id    I m thinking about changing the JPA findOne   method to Optional lt  S  gt   How to solve that   More info   This is the categoryService method   public Category findOne Long id      return categoryRepository findOne id

User · Answer

Optional api provides methods for getting the values  You can check isPresent   for the presence of the value and then make a call to get   or you can make a call to get   chained with orElse   and provide a default value   The last thing you can try doing is using  Query   over a custom method

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I always write a default method  findByIdOrError  in widely used CrudRepository repos interfaces    Repository  public interface RequestRepository extends CrudRepository lt Request  Integer gt         default Request findByIdOrError Integer id            return findById id  orElseThrow EntityNotFoundException  new

User · Answer

From at least  the 2 0 version  Spring-Data-Jpa modified findOne    Now  findOne   has neither the same signature nor the same behavior  Previously  it was defined in the CrudRepository interface as  T findOne ID primaryKey    Now  the single findOne   method that you will find in CrudRepository is the one defined in the QueryByExampleExecutor interface as   lt S extends T gt  Optional lt S gt  findOne Example lt S gt  example    That is implemented finally by SimpleJpaRepository  the default implementation of the CrudRepository interface  This method is a query by example search and you don t want that as a replacement  In fact  the method with the same behavior is still there in the new API  but the method name has changed  It was renamed from findOne   to findById   in the CrudRepository interface   Optional lt T gt  findById ID id     Now it returns an Optional  which is not so bad to prevent NullPointerException  So  the actual method to invoke is now Optional lt T gt  findById ID id   How to use that  Learning Optional usage  Here s important information about its specification   A container object which may or may not contain a non-null value  If a value is present  isPresent   will return true and get   will return the value  Additional methods that depend on the presence or absence of a contained value are provided  such as orElse    return a default value if value not present  and ifPresent    execute a block of code if the value is present     Some hints on how to use Optional with Optional lt T gt  findById ID id   Generally  as you look for an entity by id  you want to return it or make a particular processing if that is not retrieved  Here are three classical usage examples   Suppose that if the entity is found you want to get it otherwise you want to get a default value   You could write   Foo foo   repository findById id                       orElse new Foo      or  get a null default value if it makes sense  same behavior as before the API change    Foo foo   repository findById id                       orElse null     Suppose that if the entity is found you want to return it  else you want to throw an exception   You could write   return repository findById id           orElseThrow    - gt  new EntityNotFoundException id      Suppose you want to apply a different  processing according to if the entity is found or not  without necessarily throwing an exception    You could write   Optional lt Foo gt  fooOptional   fooRepository findById id   if  fooOptional isPresent          Foo foo   fooOptional get           processing with foo       else          alternative processing

User · Answer

The method has been renamed to findById      returning an Optional so that you have to handle absence yourself   Optional lt Foo gt  result   repository findById        result ifPresent it - gt           do something with the value if present result map it - gt           map the value if present Foo foo   result orElse null      if you want to continue just like before

User · Answer

Indeed  in the latest version of Spring Data  findOne returns an optional  If you want to retrieve the object from the Optional  you can simply use get   on the Optional  First of all though  a repository should return the optional to a service  which then handles the case in which the optional is empty  afterwards  the service should return the object to the controller

[java] Spring Data JPA findOne() change to Optional how to use this?

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