Java 我们如何使用旧版本的 Hibernate (~2009) 计算行数？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1372317/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How do we count rows using older versions of Hibernate (~2009)?
提问by craftsman
For example, if we have a table Books, how would we count total number of book records with hibernate?
例如，如果我们有一个 Books 表，我们如何使用 hibernate 计算书籍记录的总数？
采纳答案by Salandur
For older versions of Hibernate (<5.2):
对于旧版本的 Hibernate (<5.2)：
Assuming the class name is Book:
假设类名是 Book：
return (Number) session.createCriteria("Book")
.setProjection(Projections.rowCount())
.uniqueResult();
It is at least a Number, most likely a Long.
它至少是一个Number，最有可能是一个Long。
回答by Jon Spokes
You could try count(*)
你可以试试 count(*)
Integer count = (Integer) session.createQuery("select count(*) from Books").uniqueResult();
Where Booksis the name off the class- not the table in the database.
Books名称在哪里class- 不是数据库中的表。
回答by marioosh
In Java i usually need to return int and use this form:
在 Java 中，我通常需要返回 int 并使用这种形式：
int count = ((Long)getSession().createQuery("select count(*) from Book").uniqueResult()).intValue();
回答by Antonio
Here is what official hibernate docs tellus about this:
以下是官方休眠文档告诉我们的内容：
You can count the number of query results without returning them:
您可以计算查询结果的数量而不返回它们：
( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue()
However, it doesn't always return Integerinstance, so it is better to use java.lang.Numberfor safety.
但是，它并不总是返回Integer实例，因此java.lang.Number为了安全起见最好使用。
回答by xrcwrn
Long count = (Long) session.createQuery("select count(*) from Book").uniqueResult();
回答by rajadilipkolli
If you are using Hibernate 5+, then query will be modified as
如果您使用的是 Hibernate 5+，那么查询将被修改为
Long count = session.createQuery("select count(1) from Book")
.getSingleResult();
Or if you Need TypedQuery
或者如果你需要 TypedQuery
Long count = session.createQuery("select count(1) from Book",Long.class)
.getSingleResult();
回答by LucianoDemuru
This works in Hibernate 4(Tested).
这适用于 Hibernate 4（已测试）。
String hql="select count(*) from Book";
Query query= getCurrentSession().createQuery(hql);
Long count=(Long) query.uniqueResult();
return count;
Where getCurrentSession() is:
getCurrentSession() 在哪里：
@Autowired
private SessionFactory sessionFactory;
private Session getCurrentSession(){
return sessionFactory.getCurrentSession();
}
回答by Vlad Mihalcea
It's very easy, just run the following JPQL query:
这很简单，只需运行以下 JPQL 查询：
int count = (
(Number)
entityManager
.createQuery(
"select count(b) " +
"from Book b")
.getSingleResult()
).intValue();
The reason we are casting to Numberis that some databases will return Longwhile others will return BigInteger, so for portability sake you are better off casting to a Numberand getting an intor a long, depending on how many rows you are expecting to be counted.
我们强制转换的原因Number是某些数据库会返回Long而其他数据库会返回BigInteger，因此为了可移植性，您最好转换到 aNumber并获得 anint或 a long，具体取决于您期望计算的行数。
