Clojurians Log v2

following the Database Access chapter in Web Development with Clojure, I manage to recreate all the functions in the project. Up until the report generation section: lein new luminus reporting-example +postgres works, the migration works, then recreating the db.core namespace. when I start the repl and call for (mount.core/start #'reporting-example.db.core/*db*) I get an exception: >Caused by java.lang.ClassCastException mount.core.DerefableState cannot be cast to clojure.lang.IFn

the project copied from the Pragmatic Programmer website works. I understand that it has to do with the actual template that Luminus generates. I tried replacing some of the files with the ones from the finished project but I get into new issues. Is there a simple way to make this work with the current template @yogthos?

@adamgefen the error means that the db connection state hasn't been started

mount resolves components using the namespace hierarchy, so if a namespace isn't referenced anywhere the resources defined using defstate will not be started

ah hang on, just reread the error looks like a different problem

what does your *db* definition look like?

I'll rebuild it as I have all my steps documented and I'll post it in a few minutes, as by now I have replaced every bit of code.

hold on if you can...

sure thing

>ClassCastException mount.core.DerefableState cannot be cast to clojure.lang.IFn reporting-example.db.core/eval14346/fn--14347 (core.clj:20)

that's the original issue

(conman/bind-connection *db* "sql/queries.sql")

yeah that error typically occurs when the state isn't started

where are you running the above command?

that is in db.core

can you just paste db.core here

one problem could be that you have some code that's trying to use the connection at compile time

>(ns reporting-example.db.core (:require [cheshire.core :refer [generate-string parse-string]] [clj-time.jdbc] [clojure.java.jdbc :as jdbc] [clojure.tools.logging :as log] [conman.core :as conman] [reporting-example.config :refer [env]] [mount.core :refer [defstate]]) (:import org.postgresql.util.PGobject java.sql.Array clojure.lang.IPersistentMap clojure.lang.IPersistentVector [java.sql BatchUpdateException PreparedStatement Date Timestamp])) (defstate ^:dynamic db :start (if-let [jdbc-url (env :database-url)] (conman/connect! {:jdbc-url jdbc-url}) (do (log/warn "database connection URL was not found, please set :database-url in your config, e.g: dev-config.edn") db)) :stop (conman/disconnect! db)) (conman/bind-connection db "sql/queries.sql") (defn to-date [sql-date] (-> sql-date (.getTime) (java.util.Date))) (extend-protocol jdbc/IResultSetReadColumn Array (result-set-read-column [v ] (vec (.getArray v))) Date (result-set-read-column [v ] (to-date v)) Timestamp (result-set-read-column [v ] (to-date v)) PGobject (result-set-read-column [pgobj metadata index] (let [type (.getType pgobj) value (.getValue pgobj)] (case type "json" (parse-string value true) "jsonb" (parse-string value true) "citext" (str value) value)))) (extend-type java.util.Date jdbc/ISQLParameter (set-parameter [v ^PreparedStatement stmt idx] (.setTimestamp stmt idx (Timestamp. (.getTime v))))) (defn to-pg-json [value] (doto (PGobject.) (.setType "jsonb") (.setValue (generate-string value)))) (extend-type clojure.lang.IPersistentVector jdbc/ISQLParameter (set-parameter [v ^java.sql.PreparedStatement stmt ^long idx] (let [conn (.getConnection stmt) meta (.getParameterMetaData stmt) type-name (.getParameterTypeName meta idx)] (if-let [elem-type (when (= (first type-name) \_) (apply str (rest type-name)))] (.setObject stmt idx (.createArrayOf conn elem-type (to-array v))) (.setObject stmt idx (to-pg-json v)))))) (extend-protocol jdbc/ISQLValue IPersistentMap (sql-value [value] (to-pg-json value)) IPersistentVector (sql-value [value] (to-pg-json value)))

that looks right

where does the trace for the error point to in the project?

where do I check that?

where do you see the exception?

if you're running the app using lein run that should show the error in the terminal

yes

that's right

is there a stacktrace somewhere?

I could run it in cider and get a stack

just a minute

and what does the function around line 94 look like in core.cljc

might be easier if you put the project up on github or something so I can take a look locally

that's the let statement

are you starting mount states manually there?

There was nowhere that I defined start and stop, So whatever comes in the box with a new luminus +postgres. plus the protocol extension as in the tutorial.

but default luminus template doesn't generate the function above, the resources are started in core.clj using the following function:

(defn start-app [args]
  (doseq [component (-> args
                        (parse-opts cli-options)
                        mount/start-with-args
                        :started)]
    (log/info component "started"))
  (.addShutdownHook (Runtime/getRuntime) (Thread. stop-app)))

the *db* resource relies on the env resource from the config.clj namespace

and that resource must be started first

that code comes from mount

ah ok, so where does the stack trace to in your project

how are you getting the error

is it happening when the app starts, or when you run a command in the repl?

it happens when I run (mount.core/start #'reporting-example.db.core/*db*)

sorry, I thought I said...

and has the start-app function from the core namespace been run before then?

if you're running the app using lein run, and then connecting to nrepl that should cause start-app to run

works

brilliant, thanks.

so what was it? 🙂

I have no idea... I have to retrace what I did wrong.

Because I did try with lein run and without.

my recommendation is to always start the app using lein run, and then connect to the nrepl after

I guess I had in the back of my mind the idea that it can't work with all the different dependencies to when the book was written

this way it's closest to the way it would run standalone during deployment

and it ensures that all the resources are started correctly

Thanks Dmitri, The book is very helpful.

thanks, glad to hear it