JPA - 从计算列设置实体类属性？ [英] JPA - Setting entity class property from calculated column?

问题描述

我正在使用在Glassfish 3上运行的简单Java Web应用程序来处理JPA（持久性提供程序是EclipseLink）。到目前为止，我真的很喜欢它（netbeans / glassfish交互中的错误除外）但是我希望能够做到这一点，我不知道该怎么做。

I'm just getting to grips with JPA in a simple Java web app running on Glassfish 3 (Persistence provider is EclipseLink). So far, I'm really liking it (bugs in netbeans/glassfish interaction aside) but there's a thing that I want to be able to do that I'm not sure how to do.

我有一个映射到数据库表（article）的实体类（Article）。我正在尝试对返回计算列的数据库进行查询，但我无法弄清楚如何设置Article类的属性，以便在调用查询时属性由列值填充。

I've got an entity class (Article) that's mapped to a database table (article). I'm trying to do a query on the database that returns a calculated column, but I can't figure out how to set up a property of the Article class so that the property gets filled by the column value when I call the query.

如果我定期选择id，title，body from article查询，我会得到一个精美的Article对象列表，其中填充了id，title和body属性。这很好。

If I do a regular "select id,title,body from article" query, I get a list of Article objects fine, with the id, title and body properties filled. This works fine.

但是，如果我这样做：

Query q = em.createNativeQuery("select id,title,shorttitle,datestamp,body,true as published, ts_headline(body,q,'ShortWord=0') as headline, type from articles,to_tsquery('english',?) as q where idxfti @@ q order by ts_rank(idxfti,q) desc",Article.class);

（这是在Postgres上使用tsearch2进行全文搜索 - 这是一个特定于数据库的函数，所以我' m使用NativeQuery）

(this is a fulltext search using tsearch2 on Postgres - it's a db-specific function, so I'm using a NativeQuery)

你可以看到我正在获取一个名为headline的计算列。如何在我的文章类中添加标题属性，以便它被此查询填充？

You can see I'm fetching a calculated column, called headline. How do I add a headline property to my Article class so that it gets populated by this query?

到目前为止，我已经尝试将其设置为@Transient，但是最终只是因为它一直是空的。

So far, I've tried setting it to be @Transient, but that just ends up with it being null all the time.

推荐答案

可能没有好办法，只能手动：

There are probably no good ways to do it, only manually:

Object[] r = (Object[]) em.createNativeQuery(
    "select id,title,shorttitle,datestamp,body,true as published, ts_headline(body,q,'ShortWord=0') as headline, type from articles,to_tsquery('english',?) as q where idxfti @@ q order by ts_rank(idxfti,q) desc","ArticleWithHeadline")
    .setParameter(...).getSingleResult();

Article a = (Article) r[0];
a.setHeadline((String) r[1]);

-

@Entity
@SqlResultSetMapping(
    name = "ArticleWithHeadline",
    entities = @EntityResult(entityClass = Article.class),
    columns = @ColumnResult(name = "HEADLINE"))
public class Article {
    @Transient
    private String headline;
    ...
}

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