Failing lein uberjar when reading database from configuration

Question

I am writing a Ring / Compojure app with Clojure that fetches content for pages from database. To be able to create tests for how the content is displayed, I created prod and dev environments and when using dev environment, a mock database is used instead of the production database. I achieve this by reading the database from another file and giving it as a parameter to my routes. Here's a simplified version:

(defn www-routes [db]
    (defroutes www-routes
        (GET "/" [] ...)))

(def config (delay (load-file (.getFile (resource "config.clj")))))

(defn db []
    (if (= "dev" (:database @(force config)))
        'kipsu.db-mock
        'kipsu.database))

(def app (routes (www-routes (db)))

The setup is largely taken from the example here, with the addition of setting the database as a parameter.

This setup works great with running the tests with the mock database and displaying real content on prod environment. Things run fine when I start a lein server locally, run tests or any of the functions in lein repl. My problem comes when I'd like to create an uberjar for deploying the changes on my server.

This is where I get a NullPointerException when compiling, starting from (db) function call inside the def app. I've tried debugging with poor success and am not even 100% sure where the actual error is. All I know is the db function is never even called. Here's the stack trace:

Compiling kipsu.jdbc.json
Compiling kipsu.database
Compiling kipsu.api_converter
Compiling kipsu.web
java.lang.NullPointerException, compiling:(web.clj:124:29)
    at clojure.lang.Compiler$InvokeExpr.eval(Compiler.java:3628)
    at clojure.lang.Compiler$InvokeExpr.eval(Compiler.java:3622)
    at clojure.lang.Compiler$BodyExpr.eval(Compiler.java:5879)
    at clojure.lang.Compiler$DefExpr.eval(Compiler.java:439)
    at clojure.lang.Compiler.compile1(Compiler.java:7323)
    at clojure.lang.Compiler.compile(Compiler.java:7390)
    at clojure.lang.RT.compile(RT.java:399)
    at clojure.lang.RT.load(RT.java:444)
    at clojure.lang.RT.load(RT.java:412)
    at clojure.core$load$fn__5448.invoke(core.clj:5866)
    at clojure.core$load.doInvoke(core.clj:5865)
    at clojure.lang.RestFn.invoke(RestFn.java:408)
    at clojure.core$load_one.invoke(core.clj:5671)
    at clojure.core$compile$fn__5453.invoke(core.clj:5877)
    at clojure.core$compile.invoke(core.clj:5876)
    at user$eval9$fn__16.invoke(form-init1768231915654429312.clj:1)
    at user$eval9.invoke(form-init1768231915654429312.clj:1)
    at clojure.lang.Compiler.eval(Compiler.java:6782)
    at clojure.lang.Compiler.eval(Compiler.java:6772)
    at clojure.lang.Compiler.load(Compiler.java:7227)
    at clojure.lang.Compiler.loadFile(Compiler.java:7165)
    at clojure.main$load_script.invoke(main.clj:275)
    at clojure.main$init_opt.invoke(main.clj:280)
    at clojure.main$initialize.invoke(main.clj:308)
    at clojure.main$null_opt.invoke(main.clj:343)
    at clojure.main$main.doInvoke(main.clj:421)
    at clojure.lang.RestFn.invoke(RestFn.java:421)
    at clojure.lang.Var.invoke(Var.java:383)
    at clojure.lang.AFn.applyToHelper(AFn.java:156)
    at clojure.lang.Var.applyTo(Var.java:700)
    at clojure.main.main(main.java:37)
Caused by: java.lang.NullPointerException
    at kipsu.web$fn__4568.invoke(web.clj:115)
    at clojure.lang.Delay.deref(Delay.java:37)
    at clojure.lang.Delay.force(Delay.java:27)
    at clojure.core$force.invoke(core.clj:730)
    at kipsu.web$db.invoke(web.clj:118)
    at clojure.lang.AFn.applyToHelper(AFn.java:152)
    at clojure.lang.AFn.applyTo(AFn.java:144)
    at clojure.lang.Compiler$InvokeExpr.eval(Compiler.java:3623)
    ... 30 more
Exception in thread "main" java.lang.NullPointerException, compiling (web.clj:124:29)
    at clojure.lang.Compiler$InvokeExpr.eval(Compiler.java:3628)
    at clojure.lang.Compiler$InvokeExpr.eval(Compiler.java:3622)
    at clojure.lang.Compiler$BodyExpr.eval(Compiler.java:5879)
    at clojure.lang.Compiler$DefExpr.eval(Compiler.java:439)
    at clojure.lang.Compiler.compile1(Compiler.java:7323)
    at clojure.lang.Compiler.compile(Compiler.java:7390)
    at clojure.lang.RT.compile(RT.java:399)
    at clojure.lang.RT.load(RT.java:444)
    at clojure.lang.RT.load(RT.java:412)
    at clojure.core$load$fn__5448.invoke(core.clj:5866)
    at clojure.core$load.doInvoke(core.clj:5865)
    at clojure.lang.RestFn.invoke(RestFn.java:408)
    at clojure.core$load_one.invoke(core.clj:5671)
    at clojure.core$compile$fn__5453.invoke(core.clj:5877)
    at clojure.core$compile.invoke(core.clj:5876)
    at user$eval9$fn__16.invoke(form-init1768231915654429312.clj:1)
    at user$eval9.invoke(form-init1768231915654429312.clj:1)
    at clojure.lang.Compiler.eval(Compiler.java:6782)
    at clojure.lang.Compiler.eval(Compiler.java:6772)
    at clojure.lang.Compiler.load(Compiler.java:7227)
    at clojure.lang.Compiler.loadFile(Compiler.java:7165)
    at clojure.main$load_script.invoke(main.clj:275)
    at clojure.main$init_opt.invoke(main.clj:280)
    at clojure.main$initialize.invoke(main.clj:308)
    at clojure.main$null_opt.invoke(main.clj:343)
    at clojure.main$main.doInvoke(main.clj:421)
    at clojure.lang.RestFn.invoke(RestFn.java:421)
    at clojure.lang.Var.invoke(Var.java:383)
    at clojure.lang.AFn.applyToHelper(AFn.java:156)
    at clojure.lang.Var.applyTo(Var.java:700)
    at clojure.main.main(main.java:37)
Caused by: java.lang.NullPointerException
    at kipsu.web$fn__4568.invoke(web.clj:115)
    at clojure.lang.Delay.deref(Delay.java:37)
    at clojure.lang.Delay.force(Delay.java:27)
    at clojure.core$force.invoke(core.clj:730)
    at kipsu.web$db.invoke(web.clj:118)
    at clojure.lang.AFn.applyToHelper(AFn.java:152)
    at clojure.lang.AFn.applyTo(AFn.java:144)
    at clojure.lang.Compiler$InvokeExpr.eval(Compiler.java:3623)
    ... 30 more
Compilation failed: Subprocess failed

I'm not the most fluent with Clojure and am working with this app to learn more. Any help for steering me at the right direction from here is greatly appreciated!

Answer 1

I think your problem is because def will execute at compile time. You've done the right thing in (def config) and (defn db), but (def app) is going to cause compile time errors if it cannot find your file. To understand why let's look at def.

(def hello (println "hello"))

If you try to compile this code you'll see "hello" printed to your console at compile time and at runtime the var hello will have the value nil.

(def hello (delay (println "hello"))

(def world @hello)

The var hello now won't get evaluated at compile time, but by introducing the var world we get the exact same problem.

Now back to your specific problem. You don't want your configuration to get read at compile time, and you don't want your configuration to have to read a file from disk every single time you need it.

Not reading your configuration at compile time makes me think that maybe it should be a function. If it is then a function you can simply use memoize to ensure it doesn't read from disk every time you call that function.