How do we count rows using older versions of Hibernate (~2009)?

问题

For example, if we have a table Books, how would we count total number of book records with hibernate?

回答1:

For older versions of Hibernate (<5.2):

Assuming the class name is Book:

return (Number) session.createCriteria("Book")
                  .setProjection(Projections.rowCount())
                  .uniqueResult();

It is at least a Number, most likely a Long.

回答2:

In Java i usually need to return int and use this form:

int count = ((Long)getSession().createQuery("select count(*) from Book").uniqueResult()).intValue();

回答3:

Here is what official hibernate docs tell us about this:

You can count the number of query results without returning them:

( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue()

However, it doesn't always return Integer instance, so it is better to use java.lang.Number for safety.

回答4:

You could try count(*)

Integer count = (Integer) session.createQuery("select count(*) from Books").uniqueResult();

Where Books is the name off the class - not the table in the database.

回答5:

If you are using Hibernate 5+, then query will be modified as

Long count = session.createQuery("select count(1) from  Book")
                    .getSingleResult();

Or if you Need TypedQuery

Long count = session.createQuery("select count(1) from  Book",Long.class)
                        .getSingleResult();

回答6:

Long count = (Long) session.createQuery("select count(*) from  Book").uniqueResult();

回答7:

This works in Hibernate 4(Tested).

String hql="select count(*) from  Book";
Query query= getCurrentSession().createQuery(hql);
Long count=(Long) query.uniqueResult();
return count;

Where getCurrentSession() is:

@Autowired
private SessionFactory sessionFactory;


private Session getCurrentSession(){
return sessionFactory.getCurrentSession();
}

回答8:

It's very easy, just run the following JPQL query:

int count = (
(Number)
    entityManager
    .createQuery(
        "select count(b) " +
        "from Book b")
    .getSingleResult()
).intValue();

The reason we are casting to Number is that some databases will return Long while others will return BigInteger, so for portability sake you are better off casting to a Number and getting an int or a long, depending on how many rows you are expecting to be counted.

来源：https://stackoverflow.com/questions/1372317/how-do-we-count-rows-using-older-versions-of-hibernate-2009

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