使用clojure/korma/postgres准备了SubSelect的语句

Question

我一直在尝试在Korma中进行以下操作：

SQL：

PREPARE q (int) AS SELECT * FROM post a
    WHERE EXISTS 
        (SELECT parent_id
         FROM post_map 
         WHERE parent_id=a.id AND parent_id=$1);
EXECUTE q(1);

我最好的Korma尝试：

(defn children [parent-id]        ;; clojure
      (if (number? parent-id)
        (exec-raw (str
          "PREPARE q (int) AS SELECT * FROM post a WHERE EXISTS 
               (SELECT parent_id FROM post_map WHERE parent_id=a.id AND parent_id=$1); 
           EXECUTE q(" parent-id ")") 
         :results)))

这是我一直遇到的错误：（我真的不了解下面的::操作员：）

Failure to execute query with SQL:
PREPARE q (int) AS SELECT * FROM post a WHERE EXISTS 
          (SELECT parent_id FROM post_map WHERE parent_id=a.id AND parent_id=$1); 
       EXECUTE q(1)  ::  nil
PSQLException:
 Message: No results were returned by the query.
 SQLState: 02000
 Error Code: 0
PSQLException No results were returned by the query.  org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery (AbstractJdbc2Statement.java:274)

我认为这不是一个非常奇怪的事情，所以我想知道Korma是否不适合我的项目工作。我只是做错了吗？

更新：这是我最终做的（在我在Korma上保释后[对不起Korma]）。

(defn children [parent-id]
  (if (unsigned? parent-id)
    (sql/with-connection db
      (sql/with-query-results results
         [(str "select " field-list ", b.parent_id from post a, post_map b where a.id=b.child_id and a.id in "
               "(select child_id from post c, post_map d where c.id=d.parent_id and c.id=?)") parent-id]
           (into [] results)))))

Answer 1

korma在引擎盖下使用预先准备，它仅适用于单个语句，还为您准备。

这有效：

;; but isn't it more 'parent' than 'children'?
(defn children-raw [parent-id]
  (if (number? parent-id)
    (exec-raw [(str
                "SELECT * FROM post a WHERE EXISTS
               (SELECT parent_id FROM post_map WHERE parent_id=a.id AND parent_id=?)")
               [parent-id]]
              :results)))

但是，即使从这个小例子中很难看出，我也对您的命名/模式有些困惑。您的功能称为"儿童"，但使用（）我认为它将返回最大记录。另外，它似乎选择了 parent ，但是随着隐式加入，它总是会选择自己？

如果post_map是从id到parent_id的链接，并且您想让孩子们，我会认为更多的是：

(defentity post
  (entity-fields :id))
(defentity post_map
  (entity-fields :id :parent_id))
(defn children-dsl [parent-id]
  (if (number? parent-id)
    (select post
            (where {:id [in (subselect post_map
                                       (fields :id)
                                       (where {:parent_id parent-id}))]}))))