What s the difference between session persist and session save in Hibernate

Question

Can anyone tell me what s the advantage of persist   vs save   in Hibernate

User · Answer

Here is the difference    save    will return the id identifier when the object is saved to the database  will also save when the object is tried to do the same by opening a new session after it is detached   Persist    will return void when the object is saved to the database  will throw PersistentObjectException when tried to save the detached object through a new session

User · Answer

Actually  the difference between hibernate save   and persist   methods depends on generator class we are using  If our generator class is assigned  then there is no difference between save   and persist   methods  Because generator    assigned    means  as  a programmer we need to give the primary key value to save in the database right   Hope you know this generators concept   In case of other than assigned generator class  suppose if our generator class name is Increment means hibernate itself will assign the primary key id value into the database right  other than assigned generator  hibernate only used to take care the primary key id value remember   so in this case if we call save   or persist   method  then it will insert the record into the database normally  But here  thing is   save   method can return that primary key id value which is generated by hibernate and we can see it by long s   session save k   In this same case  persist   will never give any value back to the client  return type void  persist   also guarantees that it will not execute an INSERT statement if it is called outside of transaction boundaries  whereas in save    INSERT happens immediately  no matter if you are inside or outside of a transaction

User · Answer

From this forum post     persist   is well defined  It makes a   transient instance persistent    However  it doesn t guarantee that the   identifier value will be assigned to   the persistent instance immediately    the assignment might happen at flush   time  The spec doesn t say that  which   is the problem I have with persist          persist   also guarantees that it will   not execute an INSERT statement if it   is called outside of transaction   boundaries  This is useful in   long-running conversations with an   extended Session persistence context        A method like persist   is required        save   does not guarantee the same  it   returns an identifier  and if an   INSERT has to be executed to get the   identifier  e g   identity  generator    not  sequence    this INSERT happens   immediately  no matter if you are   inside or outside of a transaction    This is not good in a long-running   conversation with an extended   Session persistence context

User · Answer

Here are the differences that can help you understand the advantages of persist and save methods    First difference between save and persist is their return type  The  return type of persist method is void while return type of save method is Serializable object  The persist   method doesn   t guarantee that the identifier value will be assigned to the persistent state immediately  the assignment might happen at flush time  The persist   method will not execute an insert query if it is called outside of transaction boundaries  While  the save   method returns an identifier so that an insert query is executed immediately to get the identifier  no matter if it are inside or outside of a transaction  The persist method is called outside of transaction boundaries  it is useful in long-running conversations with an extended Session context  On the other hand save method is not good in a long-running conversation with an extended Session context  Fifth difference between save and persist method in Hibernate  persist is supported by JPA  while save is only supported by Hibernate    You can see the full working example from the post Difference between save and persist method in Hibernate

User · Answer

save  - As the method name suggests  hibernate save   can be used to save entity to database  We can invoke this method outside a transaction  If we use this without transaction and we have cascading between entities  then only the primary entity gets saved unless we flush the session   persist  -Hibernate persist is similar to save  with transaction  and it adds the entity object to the persistent context  so any further changes are tracked  If the object properties are changed before the transaction is committed or session is flushed  it will also be saved into database  Also  we can use persist   method only within the boundary of a transaction  so it   s safe and takes care of any cascaded objects  Finally  persist doesn t return anything so we need to use the persisted object to get the generated identifier value

User · Answer

This question has some good answers about different persistence methods in Hibernate   To answer your question directly  with save   the insert statement is executed immediately regardless of transaction state   It returns the inserted key so you can do something like this      long newKey   session save myObj     So use save   if you need an identifier assigned to the persistent instance immediately     With persist    the insert statement is executed in a transaction  not necessarily immediately   This is preferable in most cases    Use persist   if you don t need the insert to happen out-of-sequence with the transaction and you don t need the inserted key returned

User · Answer

I did some mock testing to record the difference between save   and persist     Sounds like both these methods behaves same when dealing with Transient Entity but differ when dealing with Detached Entity   For the below example  take EmployeeVehicle as an Entity with PK as vehicleId which is a generated value and vehicleName as one of its properties   Example 1   Dealing with Transient Object  Session session   factory openSession    session beginTransaction    EmployeeVehicle entity   new EmployeeVehicle    entity setVehicleName  Honda    session save entity      session persist entity   session getTransaction   commit    session close      Result   select nextval   hibernate sequence      This is for vehicle Id generated   36 insert into Employee Vehicle   Vehicle Name  Vehicle Id  values   Honda  36    Note the result is same when you get an already persisted object and save it   EmployeeVehicle entity     EmployeeVehicle session get EmployeeVehicle class  36   entity setVehicleName  Toyota    session save entity      ------- gt    instead of session update entity        session persist entity     Repeat the same using persist entity  and will result the same with new Id   say 37   honda      Example 2   Dealing with Detached Object     Session 1     Get the previously saved Vehicle Entity  Session session   factory openSession    session beginTransaction    EmployeeVehicle entity    EmployeeVehicle session get EmployeeVehicle class  36   session close        Session 2    Here in Session 2   vehicle entity obtained in previous session is a detached object and now we will try to save   persist it      i  Using Save   to persist a detached object  Session session2   factory openSession    session2 beginTransaction    entity setVehicleName  Toyota    session2 save entity   session2 getTransaction   commit    session2 close      Result   You might be expecting the Vehicle with id   36 obtained in previous session is updated with name as  Toyota    But what happens is that a new entity is saved in the DB with new Id generated for and Name as  Toyota   select nextval   hibernate sequence   insert into Employee Vehicle   Vehicle Name  Vehicle Id  values   Toyota  39    Using persist to persist detached entity      ii  Using Persist    to persist a detached    Session 1  Session session   factory openSession    session beginTransaction    EmployeeVehicle entity    EmployeeVehicle session get EmployeeVehicle class  36   session close        Session 2    Here in Session 2   vehicle entity obtained in previous session is a detached object and now we will try to save   persist it      i  Using Save   to persist a detached Session session2   factory openSession    session2 beginTransaction    entity setVehicleName  Toyota    session2 persist entity   session2 getTransaction   commit    session2 close      Result   Exception being thrown   detached entity passed to persist   So  it is always better to use Persist   rather than Save   as save has to be carefully used when dealing with Transient object    Important Note   In the above example   the pk of vehicle entity is a generated value   so when using save   to persist a detached entity   hibernate generates a new id to persist   However if this pk is not a generated value than it is result in a exception stating key violated

User · Answer

I have done good research on the save   vs  persist   including running it on my local machine several times  All the previous explanations are confusing and incorrect  I compare save   and persist   methods below after a thorough research  Save    Returns generated Id after saving  Its return type is Serializable  Saves the changes to the database outside of the transaction  Assigns the generated id to the entity you are persisting  session save   for a detached object will create a new row in the table   Persist    Does not return generated Id after saving  Its return type is void  Does not save the changes to the database outside of the transaction  Assigns the generated Id to the entity you are persisting  session persist   for a detached object will throw a PersistentObjectException  as it is not allowed   All these are tried tested on Hibernate v4 0 1

User · Answer

Basic rule says that    For Entities with generated identifier    save     It returns an entity s identifier immediately in addition to making the object persistent  So an insert query is fired immediately    persist     It returns the persistent object  It does not have any compulsion of returning the identifier immediately so it does not guarantee that insert will be fired immediately  It may fire an insert immediately but it is not guaranteed  In some cases  the query may be fired immediately while in others it may be fired at session flush time    For Entities with assigned identifier    save    It returns an entity s identifier immediately  Since the identifier is already assigned to entity before calling save  so insert is not fired immediately  It is fired at session flush time   persist     same as save  It also fire insert at flush time   Suppose we have an entity which uses a generated identifier as follows     Entity  Table name  USER DETAILS   public class UserDetails        Id      Column name    USER ID        GeneratedValue strategy GenerationType AUTO      private int userId        Column name    USER NAME       private String userName       public int getUserId             return userId            public void setUserId int userId            this userId   userId            public String getUserName             return userName            public void setUserName String userName            this userName   userName            save           Session session   sessionFactory openSession        session beginTransaction        UserDetails user   new UserDetails        user setUserName  Gaurav        session save user      Query is fired immediately as this statement is executed      session getTransaction   commit        session close      persist           Session session   sessionFactory openSession        session beginTransaction        UserDetails user   new UserDetails        user setUserName  Gaurav        session persist user      Query is not guaranteed to be fired immediately  It may get fired here      session getTransaction   commit       If it not executed in last statement then It is fired here      session close      Now suppose we have the same entity defined as follows without the id field having generated annotation i e  ID will be assigned manually    Entity  Table name  USER DETAILS   public class UserDetails        Id      Column name    USER ID       private int userId        Column name    USER NAME       private String userName       public int getUserId             return userId            public void setUserId int userId            this userId   userId            public String getUserName             return userName            public void setUserName String userName            this userName   userName            for save      Session session   sessionFactory openSession    session beginTransaction    UserDetails user   new UserDetails    user setUserId 1   user setUserName  Gaurav    session save user      Query is not fired here since id for object being referred by user is already available  No query need to be fired to find it  Data for user now available in first level cache but not in db  session getTransaction   commit      Query will be fired at this point and data for user will now also be available in DB session close      for persist      Session session   sessionFactory openSession    session beginTransaction    UserDetails user   new UserDetails    user setUserId 1   user setUserName  Gaurav    session persist user      Query is not fired here Object is made persistent  Data for user now available in first level cache but not in db  session getTransaction   commit      Query will be fired at this point and data for user will now also be available in DB session close      The above cases were true when the save or persist were called from within a transaction   The other points of difference between save and persist are     save   can be called outside a transaction  If assigned identifier is used then since id is already available  so no insert query is immediately fired  The query is only fired when the session is flushed   If generated identifier is used   then since id need to generated  insert is immediately fired  But it only saves the primary entity  If the entity has some cascaded entities then those will not be saved in db at this point  They will be saved when the session is flushed  If persist   is outside a transaction then insert is fired only when session is flushed no matter what kind of identifier  generated or assigned  is used  If save is called over a persistent object  then the entity is saved using update query

User · Answer

It completely answered on basis of  generator  type in ID while storing any entity  If value for generator is  assigned  which means you are supplying the ID  Then it makes no diff in hibernate for save or persist  You can go with any method you want  If value is not  assigned  and you are using save   then you will get ID as return from the save   operation   Another check is if you are performing the operation outside transaction limit or not  Because persist   belongs to JPA while save   for hibernate  So using persist   outside transaction boundaries will not allow to do so and throw exception related to persistant  while with save   no such restriction and one can go with DB transaction through save   outside the transaction limit

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