QueryDSL - 如何加入子查询的并集 [英] QueryDSL - how to join to a union of subqueries

问题描述

我正在使用QueryDSL构建SQL查询，该查询包含在联合中连接的多个子查询。这是我查询的基础：

I'm building a SQL query with QueryDSL that contains several subqueries joined in a union. This is the base of my query:

QTransaction t = QTransaction.transaction;
query = query.from(t).where(t.total.gt(BigDecimal.ZERO));

然后，我有几个子查询来获取与事务关联的客户端名称。我已经减少了两个例子：

I then have several subqueries to obtain client names associated with a transaction. I've cut down to two for the example:

SQLSubQuery subQuery = new SQLSubQuery();
subQuery = subQuery.from(t).join(t.fk462bdfe3e03a52d4, QClient.client);
ListSubQuery clientByPaid = subQuery.list(t.id, bt.paidId, QClient.client.name.as("clientname"));

subQuery = new SQLSubQuery();
subQuery = subQuery.from(t).where(t.paidId.isNull(), t.clientname.isNotNull());
ListSubQuery clientByName = subQuery.list(t.id, Expressions.constant(-1L), t.clientname.as("clientname"));

如何将这些组合在一起，并使用我的主查询加入联合？这是我目前的尝试：

How do I union these together, and join the union with my main query? This is my current attempt:

subQuery = new SQLSubQuery();
subQuery = subQuery.from(subQuery.unionAll(clientByPaid,clientByName).as("namequery"));


query = query.leftJoin(subQuery.list(
            t.id, Expressions.path(Long.class, "clientid"),
                    Expressions.stringPath("clientname")),
                    Expressions.path(List.class, "namequery"));

这会编译，但在我尝试 query.count时会在运行时生成无效的SQL （）。可能的错误：

This compiles, but generates invalid SQL at runtime when I attempt query.count(). Likely mistakes:

• 子查询联合的语法。


• <$>之间的连接c $ c> .as（...）表达式，用于命名子查询结果列和 leftJoin 中使用的路径表达式。

• The syntax for the union of subqueries.
• The connection between the .as(...) expression that names the subquery result columns and the path expression used in the leftJoin.

推荐答案

修正了它。主要的错误是我错过了左连接中的 子句，但为了在 >条件我必须更加小心命名子查询。文档对构造访问子查询结果的路径有点了解，所以这是示例。

Fixed it. The main bug was that I'd missed out the on clause in the left join, but in order to express the on condition I had to be much more careful about naming the subqueries. The documentation is a little light on constructing paths to access subquery results, so here's the example.

联合中的第一个查询设置列名：

The first query in the union sets the column names:

SQLSubQuery subQuery = new SQLSubQuery();
subQuery = subQuery.from(t).join(t.fk462bdfe3e03a52d4, QClient.client);
ListSubQuery clientByPaid = subQuery.list(t.id.as("id"), t.paidId.as("clientid"),
                                QClient.client.name.as("clientname"));

subQuery = new SQLSubQuery();
subQuery = subQuery.from(t).where(t.paidId.isNull(), t.clientname.isNotNull());
ListSubQuery clientByName = subQuery.list(t.id, Expressions.constant(-1L), 
                                  t.clientname);

我现在需要构建一个路径表达式来引用我的内部查询。我在路径中使用哪个类似乎并不重要，所以我选择了Void来强调这一点。

I now need to build a path expressions to refer back to my inner query. It doesn't seem to matter which class I use for the path, so I've picked Void to emphasize this.

subQuery = new SQLSubQuery();
Path innerUnion = Expressions.path(Void.class, "innernamequery");
subQuery = subQuery.from(subQuery.union(clientByPaid,clientByName).as(innerUnion));

还有一个表达的路径表达式条款。请注意，我加入了union查询的 list（），每个列都使用之前定义的 innerUnion 路径选择。

And a further path expression to express the on clause. Note that I join to a list() of the union query, with each column selected using the innerUnion path defined earlier.

Path namequery = Expressions.path(Void.class, "namequery");
query = query.leftJoin(subQuery.list(
                Expressions.path(Long.class, innerUnion, "id"),
                Expressions.path(Long.class, innerUnion, "clientid"),
                Expressions.stringPath(innerUnion, "clientname")),
              namequery)
          .on(t.id.eq(Expressions.path(Long.class, namequery, "id")));

这篇关于QueryDSL - 如何加入子查询的并集的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！