如何将记录添加到现有地图？

Question

I have a map obtained from running a sql query.

(defn print-info
  [rs]
  (doseq [req rs]
    (let [rs1 req]
      (println "rs1" rs1))))

(defn display-info
  [uname]
  (sql/with-connection
     db 
     (sql/with-query-results rs
                             ["Select * from user"]
                             (print-info rs))))

Now i have copied the result set into another map. Is there any way to add another record to this existing map and return this new map to another function ?

Answer 1

If you use the non-deprecated query syntax which was explained in your other question , you can use the :row-fn to manipulate each record in a resultset. A default row is a map, so if you use only functions that return a map (like in this case select-keys ), you can just use assoc to add a new key-value pair to the map.

(query db ["select * from user"]
          :row-fn #(assoc (select-keys % [:name]) :type :user))

Answer 2

Generally speaking when I want to make a fix to a record I'll use merge , which merges any number of maps in a left-to-right direction. Thus:

user=> (merge {:foo 1 :bar 2 :ban 3} {:bar 20} {:ban 300})
{:foo 1, :bar 20, :ban 300}

Although the assoc approach mentioned above also works, I find merge generally more useful and more flexible.

This applies to anything represented as a map, of course, not just records!

As an aside I'd strongly recommend using [Korma| http://sqlkorma.com/] for your database queries.