updating multiple rows using JPA

问题

I want to update all fields of a table that has value of colum NAME as 'PCNAME'. The table name which i want to update is XYZ.I want to update only some fields and not keep some unchanged.

This will affect many rows and not a single row as there will be many rows with NAME='PCNAME' How can i do it using JPA.I have entity class associated with this table.

回答1:

You can either do it the object oriented way or using an update query.

Object oriented:

public void setNameOfAllEntities(String newname){
    List<MyEntity> items =
        entityManager.createQuery("from MyEntity", MyEntity.class)
            .getResultList();
    for(MyEntity entity : items){
        entity.setName(newname);
    }
}

With Update Query (untested):

public void setNameOfAllEntities(final String newname){

    final int changes =
        entityManager.createQuery("update MyEntity set name = :name")
            .setParameter("name", newname)
            .executeUpdate();

    System.out.println(changes + " rows changed");

}

Obviously, the second version performs better.

回答2:

seanizer's answer is correct (+1) and a bulk update would be indeed nice for this use case. But you must take some precautions with bulk update operations. To paraphrase the JPA specification:

bulk updates bypass optimistic locking checks (so you must manually increment the version column and/or manually validate the version column if desired)
the persistence context is not synced with the result of bulk operations (so bulk operations should be performed in a separate transaction or at the very beginning of a transaction, before loading the state of any entity that might be affected).

My suggestion would thus be to at least increment the version column to avoid concurrency problem with other threads:

UPDATE XYZ xyz
SET xyz.name = :newname, xyz.version = xyz.version + 1

And to perform it in a separate transaction or before loading any XYZ as previously explained.

References

JPA 1.0 specification
- Section 4.10 "Bulk Update and Delete Operations"

来源：https://stackoverflow.com/questions/4069513/updating-multiple-rows-using-jpa

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