save vs saveOrUpdate in Hibernate

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In Hibernate, both save and saveOrUpdate methods are used to store an object in the database, but they are used in different scenarios and have different behaviors. In this post, we will discuss the difference between Session.save() and Session.saveOrUpdate() methods in Hibernate with an example.
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save Method 

Behavior: Inserts the object into the database. 

Identifier Generation: If the object's identifier (primary key) is not set, Hibernate will generate one based on the defined generation strategy. 

Exception Handling: If the object with the same identifier already exists in the database, calling save will result in a primary key violation, leading to an exception. 

Use Case: Typically used when you want to save a new entity and are relying on Hibernate to generate the identifier. 

saveOrUpdate Method 

Behavior: Depending on the object's state, this method will either save a new object or update an existing one. 

Identifier Checking: If the identifier is null, it considers the object as transient and will save it. If the identifier is not null, it will check the session to see if the object is already associated; if it is, it will update the existing object. 

Exception Handling: This method does not generally throw an exception due to identifier conflicts, as it will update the existing record if it finds one. 

Use Case: Use this method when you want to either save a new entity or update an existing one, and you are not sure whether the object is already present in the database or not. 

Session save and saveOrUpdate Method Examples

Session.save() method example: 

    The below code uses Session.save() method to insert a new record into a database: 
    public void saveExample(Student student) {
    Transaction transaction = null;
    try (Session session = HibernateJavaConfig.getSessionfactory().openSession()) {

        // start the transaction
        transaction = session.beginTransaction();

        // save student entity
        Serializable id = session.save(student);
        System.out.println("database table id -> " + id);
        // commit transaction
        transaction.commit();

    } catch (Exception e) {
        if (transaction != null) {
            transaction.rollback();
        }
    }
}

    Session.saveOrUpdate() method example: 

    The below code uses Session.saveOrUpdate() method INSERT or UPDATE a record based on the existence of the record in a database. 
    public void saveOrUpdateExample(Student student) {
      Transaction transaction = null;
      try(Session session = HibernateJavaConfig.getSessionfactory().openSession()){
   
         // start the transaction
         transaction = session.beginTransaction();
   
         // first save student entity using saveOrUpdate() method
         session.saveOrUpdate(student);   
   
         // get the student object
         Student student2 = session.get(Student.class, student.getId());
   
         // update the student2 object   
         student2.setFirstName("Prabhas");
         student2.setEmail("[email protected]");
   
         // update student entity using saveOrUpdate() method
         session.saveOrUpdate(student2);
   
         // commit transaction
         transaction.commit();
   
     }catch (Exception e) {
         if(transaction != null) {
          transaction.rollback();
      }
}

    Summary

    Here's a table summarizing the key differences:
    Feature save() Method saveOrUpdate() Method
    Behavior Inserts the object Inserts or updates the object
    Identifier Generation Generates if not exist Saves if null, updates if not null
    Exception Handling Throws an exception if the identifier exists Updates if identifier exists
    Use Case Saving new entities Saving new entities or updating existing ones

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