postgresql - 使用 Clojure/Korma/Postgres 的带有子选择的准备好的语句

Question

我一直尝试在 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: (我不太理解下面的 :: 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)

我认为用查询来做这件事并不奇怪，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:这就是我最终所做的(在我放弃 Korma [抱歉 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)))))

Answer 1

Korma 在幕后使用 do-prepared，它只对单个语句有效，同时也会为你准备好它。

这个有效:

;; 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)))

尽管从这个小示例中很难分辨，但我对您的命名/架构感到有些困惑。您的函数称为“childREN”，但使用 EXISTS() 我认为它最多会返回一条记录。此外，它似乎选择了父级，但是通过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，并且您想得到 child ，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}))]}))))