Java 如何使用 JPA Criteria API 解析 Oracle 的“rownum”伪列？
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How to resolve Oracle's 'rownum' pseudocolumn with JPA Criteria API?
提问by gadon
I would like to get first row from database using JPA Criteria. I use JPA, Hibernate 4.2.7. In SQL, statement looks like:
我想使用 JPA Criteria 从数据库中获取第一行。我使用 JPA，休眠 4.2.7。在 SQL 中，语句如下所示：
SELECT * FROM houses WHERE rownum = 1;
My Java code to achive that looks like:
我要实现的 Java 代码如下所示：
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<House> query = builder.createQuery(House.class);
Root<House> root = query.from(House.class);
query.select(root).where(builder.equal(root.get("rownum"), 1));
TypedQuery<House> tQuery = entityManager.createQuery(query);
House house = tQuery.getSingleResult();
But 'rownum' pseudocolumn cannot be resolved, I get exception:
但是 'rownum' 伪列无法解析，出现异常：
java.lang.IllegalArgumentException: Unable to resolve attribute [rownum] against path
at org.hibernate.ejb.criteria.path.AbstractPathImpl.unknownAttribute(AbstractPathImpl.java:120)
at org.hibernate.ejb.criteria.path.AbstractPathImpl.locateAttribute(AbstractPathImpl.java:229)
at org.hibernate.ejb.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:200)
Is is possible, and if so, how to get 'rownum' pseudocolumn with Criteria API? Thanks for any suggestions.
是可能的，如果是这样，如何使用 Criteria API 获取“rownum”伪列？感谢您的任何建议。
采纳答案by bradleyfitz
You can accomplish this using setFirstResult and setMaxResults.
您可以使用 setFirstResult 和 setMaxResults 完成此操作。
session.createCriteria(Foo.class)
.setFirstResult(0)
.setMaxResults(1);
回答by djavaphp
you can set rownum or limits in property of query;
您可以在查询属性中设置 rownum 或限制；
Query q =entityManager.createQuery("select * from employee_table");
q.setFirstResult(0);
q.setFirstResult(0);
q.setMaxResults(30);
q.setMaxResults(30);
