[英]Using :row-fn failing in clojure.jdbc query call
此代码有效,打印给定表中的行:
(defn count-extreferences-subset [config]
(let [emr-dbs (:emr-databases config)]
(println "Counting external references: " emr-dbs)
(jdbc/with-db-connection [dbconn (:db-spec (first emr-dbs))]
(let [q "SELECT * FROM LOCREG"
rs (jdbc/query dbconn [q])]
(dorun (map println rs))))))
根据clojure.jdbc中的文档,这也应该起作用,但是应该在实现结果集时打印行(防止大型结果集出现内存溢出):
(defn count-extreferences-subset [config]
(let [emr-dbs (:emr-databases config)]
(println "Counting external references: " emr-dbs)
(jdbc/with-db-connection [dbconn (:db-spec (first emr-dbs))]
(let [q "SELECT * FROM LOCREG"
_ (jdbc/query dbconn [q] {:row-fn println})]))))
但是,此操作在运行时失败,但以下情况除外:
java.lang.IllegalArgumentException: No value supplied for key: {:row-fn #object[clojure.core$println 0x46ed7a0e "clojure.core$println@46ed7a0e"]}
知道为什么:row-fn选项使用失败吗?
我相信花括号是问题所在。 您的代码应遵循以下模式:
(jdbc/query db-spec
["select name, cost from fruit where cost = 12"]
:row-fn add-tax)
您可以在The Clojure Cookbook中找到更多信息。 我强烈建议购买副本!
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