1

我一直在尝试在 Korma 中执行以下操作但无济于事：

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)))

这是我不断收到的错误：（ 我不太了解::下面的运算符：）

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)

我不认为这对查询来说是一件非常奇怪的事情，所以我想知道 Korma 是否不适合我的项目。我只是做错了吗？

更新：这就是我最终做的事情（在我放弃 Korma [对不起 Korma] 之后）。

(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)))))
4

1 回答 1

2

Korma 在后台使用 do-prepared，它仅适用于单个语句，并且还为您准备了它。

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)))

不过，我对您的命名/模式感到有些困惑，即使很难从这个小例子中分辨出来。您的函数称为“childREN”，但使用 EXISTS() 我认为它将返回最多一条记录。另外，它似乎选择了parent，但是使用隐式连接它总是会选择自己？

如果 post_map 是从 id 到 parent_id 的链接，并且您想获得孩子，我会考虑更多：

(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}))]}))))
于 2013-03-09T17:51:08.777 回答