Question

我正在尝试使用函数中的宏：

(defentity student
  (pk :id)
  (table :student)
  (entity-fields :id :name :age :class)
  (database prod))

(defn query-student [cond]
  (select student
    (where cond)))

我测试了它：

(select student
  (where {:age [> 13]}))

(query-student '{:age [> 13]})

它看起来不错，但是这个

(select student
  (where (or {:age [> 13]} {:class [in ["1" "2" "3"]]})))

(query-student '(or {:age [> 13]} {:class [in ["1" "2" "3"]]}))

不起作用！

Failure to execute query with SQL:
SELECT "student".* FROM "student" WHERE (or {:age [> 13]} {:class [in ["1" "2" "3"]]})  ::      []
PSQLException:
 Message: ERROR: syntax error at or near "or"
  Location：42
 SQLState: 42601
 Error Code: 0
PSQLException ERROR: syntax error at or near "or"
  Location：42  org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse  (QueryExecutorImpl.java:2101)

我想知道为什么？有什么问题？

Answer 1

在Korma中，where是一个宏，因此您的第二个示例将列表文字传递给它，而不是让宏有机会评估表单。

尝试将query-student功能更改为宏，而不是沿着这些行

(defmacro query-student [cond]
  `(select student
    (where ~cond)))

作为额外奖励，您在使用宏时无需引用表单：

(query-student (or {:age [> 13]} {:class [in ["1" "2" "3"]]}))

希望这有帮助。

Clojure Korma：如何在函数中使用宏？

1 个答案: