hibernate - 使用连接或子查询将 SQL 查询转换为动态查询

Question

我有一个 SQL 查询（2 个变体），我需要将它与动态查询一起使用。

在 SQL 中看起来是这样（变体 1 // 通过子查询）：

SELECT AssetEntry.entryId , (
              SELECT COUNT(*)
              FROM `MBMessage`
              WHERE classPK = AssetEntry.classPK
            ) AS comments
            FROM `AssetEntry`
            ORDER BY comments DESC

或者带有连接和组的替代查询：

SELECT AssetEntry.entryId, count(MBMessage.classPK)
 FROM `AssetEntry`
 JOIN MBMessage ON (AssetEntry.classPK = MBMessage.classPK)
 GROUP BY MBMessage.classPK

两个 SQL 查询显示完全相同！

现在我需要使用其中之一作为动态查询。我不知道如何进行连接，也不知道如何在投影中进行子查询？！

有谁能够帮我？谢谢

---

我必须用 custom-sql 来做到这一点。

Answer 1

Your requirement is a really specific case, which requires an aggregate-function in the SELECT statement.

I would suggest using Custom query (also known as custom-sql in liferay) with finders in your case, instead of a DynamicQuery.

DynamicQuery API has limitations and will not work in your case (speaking from experience, so if somebody else has other opinions or facts regarding the below points I would be more than happy to know):

1. Joins are not possible with DynamicQuery.
2. Its possible to return a count or to return an individual columns value using Projection but not possible to return a column and count to-gather using projections.
3. Can use sub-query with DynamicQuery using projections but I don't think you can use a sub-query in the select statement with DynamicQuery.

Answer 2

您还有另一种方法，使用 AssetEntryQuery。

AssetEntryQuery aeq = new AssetEntryQuery();
aeq.setClassName(MBMessage.class.getName());
aeq.set.... (Add any other criterions if you want to)
List<AssetEntry> assetEntries = AssetEntryServiceUtil.getEntries(aeq);