Page History

IMPORTANT: Load vs Get

There is a difference between Hibernate's load and get methods for retrieving data that is important in checking for concurrent updates:

• load does not issue a SQL SELECT statement to retrieve data. It simply creates a proxy object that follows the structure of the relevant domain class.
• get issues an immediate SQL SELECT statement, creating a new domain class containing the data read from the database.

The reason this is important for concurrent update checking is that a proxy object generated by a load will not contain the version information we need. Our scheme depends on the version being loaded at the start of a

with two sessions working with an object with the same identifier. Initial version for object in DB is 10.

    Session 1                  Session 2

    ---------                  ---------

    Load object

    Wait a while..

                               Load object

                               Modify object property

                               [triggers db 'select' -

                                version read as 10]

                               Commit

                               [triggers db update,

                                version modified to 11]

    Modify object property

      [triggers db 'select' -

      version read as 11]

    Commit

      [triggers db update,

      version modified to 12]

We actually want session 1's commit to fail with an optimistic lock exception, but it will succeed here.

Using "get" instead of "load" works around the problem, because get will immediately issue a select, and the version numbers will be loaded at the correct times for the optimistic lock checking.

We actually want session 1's commit to fail with an optimistic lock exception, but it will succeed here.

Using "get" instead of "load" works around the problem, because get will immediately issue a select, and the version numbers will be loaded at the correct times for the optimistic lock checking.