转载：criteria.setProjection(Projections.rowCount()

、

今天把myblog用sql server部署了一下，可是发现分页查询的时候出现错误，看控制台报错说语句有错,由来发现分页的时候先查询总记录数目的那条语句出错了

select count(*) as y0_ from myblog_Blog this_ inner join myblog_Blog_Category categories3_ on this_.id=categories3_.blogId inner join myblog_Category category1_ on categories3_.categoryId=category1_.id where category1_.id=? order by this_.postTime desc

原来开发的时候我是用的mysql，没有任何问题。原因就在最后面的order by 语句，sql server 在select count(*)里面不能用 order by。然后跟踪代码发现:

    public PaginationSupport getBlogsByCategoryByPage(final String categoryId, final int startIndex, final int pageSize) {
        return (PaginationSupport) getHibernateTemplate().execute(new HibernateCallback() {
            public Object doInHibernate(Session session) throws HibernateException {
                Criteria criteria = session.createCriteria(Blog.class);
                Criteria cateCriteria = criteria.createCriteria("categories");
                cateCriteria.add(Expression.eq("id",categoryId));
                criteria.addOrder(Order.desc("postTime"));
                int totalCount = ((Integer) criteria.setProjection(Projections.rowCount())
                        .uniqueResult()).intValue();
                criteria.setProjection(null);

                List items = criteria.setFirstResult(startIndex).setMaxResults(pageSize).list();
                List blogs = new ArrayList();
                for(Iterator ite = items.iterator(); ite.hasNext();) {
                    Object[] objs = (Object[])ite.next();
                    blogs.add(objs[1]);
                }
                PaginationSupport ps = new PaginationSupport(blogs, totalCount, pageSize, startIndex);
                return ps;
            }
        }, true);
    }

原来问题就在Criteria.addOrder(Order.desc("postTime"));这句话的位置上面，int totalCount = ((Integer) criteria.setProjection(Projections.rowCount())
.uniqueResult()).intValue();
这句话的时候就会生成上面那句话，如果在这之前addOrder就会出现问题，如果你用mysql不会出现问题，如果你用sql server就会报错。解决方法就是把addOrder语句放到totalCount下面就可以了。

    public PaginationSupport getBlogsByCategoryByPage(final String categoryId, final int startIndex, final int pageSize) {
        return (PaginationSupport) getHibernateTemplate().execute(new HibernateCallback() {
            public Object doInHibernate(Session session) throws HibernateException {
                Criteria criteria = session.createCriteria(Blog.class);
                Criteria cateCriteria = criteria.createCriteria("categories");
                cateCriteria.add(Expression.eq("id",categoryId));
                int totalCount = ((Integer) criteria.setProjection(Projections.rowCount())
                        .uniqueResult()).intValue();
                criteria.setProjection(null);

                /*
                 * Fix a bug ,Order must add after get the totalCount,
                 * beacuse SqlServer not support order by in the select count(*).
                 */
                criteria.addOrder(Order.desc("postTime"));
                List items = criteria.setFirstResult(startIndex).setMaxResults(pageSize).list();
                List blogs = new ArrayList();
                for(Iterator ite = items.iterator(); ite.hasNext();) {
                    Object[] objs = (Object[])ite.next();
                    blogs.add(objs[1]);
                }
                PaginationSupport ps = new PaginationSupport(blogs, totalCount, pageSize, startIndex);
                return ps;
            }
        }, true);
    }

这样生成的sql语句就是这样的。