休眠排序依据,最后为空值

鉴于 HHH-465 由于Steve Ebersole给出的原因,您最好的选择是使用 CustomNullsFirstInterceptor 附加到该问题的全局或专门用于更改SQL语句。

我在下面为读者发布(归功于Emilio Dolce):

public class CustomNullsFirstInterceptor extends EmptyInterceptor {

    private static final long serialVersionUID = -3156853534261313031L;

    private static final String ORDER_BY_TOKEN = "order by";

    public String onPrepareStatement(String sql) {

        int orderByStart = sql.toLowerCase().indexOf(ORDER_BY_TOKEN);
        if (orderByStart == -1) {
            return super.onPrepareStatement(sql);
        }
        orderByStart += ORDER_BY_TOKEN.length() + 1;
        int orderByEnd = sql.indexOf(")", orderByStart);
        if (orderByEnd == -1) {
            orderByEnd = sql.indexOf(" UNION ", orderByStart);
            if (orderByEnd == -1) {
                orderByEnd = sql.length();
            }
        }
        String orderByContent = sql.substring(orderByStart, orderByEnd);
        String[] orderByNames = orderByContent.split("\\,");
        for (int i=0; i<orderByNames.length; i++) {
            if (orderByNames[i].trim().length() > 0) {
                if (orderByNames[i].trim().toLowerCase().endsWith("desc")) {
                    orderByNames[i] += " NULLS LAST";
                } else {
                    orderByNames[i] += " NULLS FIRST";
                }
            }
        }
        orderByContent = StringUtils.join(orderByNames, ",");
        sql = sql.substring(0, orderByStart) + orderByContent + sql.substring(orderByEnd); 
        return super.onPrepareStatement(sql);
    }

}

如前所述,此功能已在Hibernate 4.2.x和4.3.x版本中实现。

例如:

Criteria criteria = ...;
criteria.addOrder( Order.desc( "name" ).nulls(NullPrecedence.FIRST) );

Hibernate v4.3 JavaDocs的灵活性较低 here .

您可以在Hibernate属性中配置“Nulls First”/“Nulls Last”,以便默认情况下任何条件调用都会拾取它: hibernate.order_by.default_null_ordering=last (或) =first )

见 this hibernate commit 详情。

以下是我对班级的最新更新(帕斯卡·蒂凡特):

for (int i = 0; i < orderByNames.length; i++) {
    if (orderByNames[i].trim().length() > 0) {
        String orderName = orderByNames[i].trim().toLowerCase();
        if (orderName.contains("desc")) {
            orderByNames[i] = orderName.replace("desc", "desc NULLS LAST");
        } else {
            orderByNames[i] = orderName.replace("asc", "asc NULLS FIRST");
        }
    }
}

这解决了问题:

如果SQL在11年4月1日星期六14:52的订单后有限制/偏移,则此操作将中断。

下面还介绍了如何在JPA(Hibernate)中使用它:

Session session = entityManager.unwrap(Session.class);
Session nullsSortingProperlySession = null;
try {
    // perform a query guaranteeing that nulls will sort last
    nullsSortingProperlySession = session.getSessionFactory().withOptions()
        .interceptor(new GuaranteeNullsFirstInterceptor())
        .openSession();
} finally {
    // release the session, or the db connections will spiral
    try {
        if (nullsSortingProperlySession != null) {
            nullsSortingProperlySession.close();
        }
    } catch (Exception e) {
        logger.error("Error closing session", e);
    }
}

我在Postgres上测试过,它修复了“空值高于非空值”的问题。

另一个变种,如果您动态创建SQL并且不使用标准API:

按合并(,'0')[asc desc]排序

这适用于varchar或numeric列。

There appears to be a change request/bug ticket open for this