REPL instructions in migrations.html not working

[winks]

To interactively create a new migration, https://luminusweb.com/docs/migrations.html tells you to do this:

(mount.core/start  #'<app>.db.core/*db*)
(user/create-migration "add-users-table")

I can not get this to work. Fresh sample project created this week via lein new luminus foobar +postgres, then adjusting :database-url in dev-config.edn, the db connection is known to work via lein run.

This is what I get:

$ cd foobar
$ lein repl

user=> (mount.core/start #'foobar.db.core/*db*)
Execution error (ClassCastException) at foobar.db.core/eval13540$fn (core.clj:14).
class mount.core.DerefableState cannot be cast to class clojure.lang.IFn (mount.core.DerefableState is in unnamed module of loader clojure.lang.DynamicClassLoader @57540fd0; clojure.lang.IFn is in unnamed module of loader 'app')

### this is the error that confuses me

user=> (user/start)
2021-12-30 09:48:46,579 [nREPL-session-b1f4b012-2cd9-4cfa-87a4-e9f735c8e430] ERROR luminus.http-server - server failed to start on port: 3000 
java.lang.RuntimeException: java.net.BindException: Address already in use

# this is not the problem, I know it's running, but I was playing around a bit

user=> (user/create-migration "foo" )
nil

### nothing happened

user=> (mount.core/start #'foobar.db.core/*db*)
{:started []}

### no more error

user=> (user/create-migration "change-something" )
nil

### still nothing happened

Also the line before the mount.start reads:

(defstate ^:dynamic *db*
  :start (conman/connect! {:jdbc-url (env :database-url)})
  :stop (conman/disconnect! *db*))

whereas in the code it is currently

(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*))

and I can't tell if that's a simplified version by default, or if it has changed meanwhile, or something else

[yogthos]

The problem is that your *db* connection is not being started until (user/start) is called. The address already in use error indicates that one of the resources defined using defstate is trying to start on a port that's currently being used. If you're getting nil output that should be fine, did you look if the file was created on the filesystem after running the command?

[winks]

The problem is that your db connection is not being started until (user/start) is called.

Yes, that was my original point, the docs tell you to do X, but you need to to Y which isn't pointed out

The address already in use error indicates that one of the resources defined using defstate is trying to start on a port that's currently being used.

Yes, that is the only part that was unsurprising :)

If you're getting nil output that should be fine, did you look if the file was created on the filesystem after running the command?

The first one failed (user/create-migration "foo" ) no migrations generated.

The second one succeeded (user/create-migration "change-something" ) but only after the undocumented call to user/start.

I'm mostly wondering if the version from the docs with just mount.core/start can be made to work (again?), as described.

[yogthos]

Just to be clear, when you run (mount.core/start #'<app>.db.core/*db*) you replace <app> with the actual namespace from your app?

[winks]

Yes of course.

$ lein new luminus migtest +postgres
Generating a Luminus project.
$ cd migtest 
$ vi dev-config.edn  # for db credentials
$ find resources/migrations 
resources/migrations
resources/migrations/20211230150621-add-users-table.down.sql
resources/migrations/20211230150621-add-users-table.up.sql
$ lein repl
nREPL server started on port 33943 on host 127.0.0.1 - nrepl://127.0.0.1:33943
REPL-y 0.5.1, nREPL 0.9.0
Clojure 1.10.3
OpenJDK 64-Bit Server VM 11.0.13+8-Ubuntu-0ubuntu1.18.04
    Docs: (doc function-name-here)
          (find-doc "part-of-name-here")
  Source: (source function-name-here)
 Javadoc: (javadoc java-object-or-class-here)
    Exit: Control+D or (exit) or (quit)
 Results: Stored in vars *1, *2, *3, an exception in *e

user=> (mount.core/start #'migtest.db.core/*db*)
Execution error (ClassCastException) at migtest.db.core/eval13540$fn (core.clj:14).
class mount.core.DerefableState cannot be cast to class clojure.lang.IFn (mount.core.DerefableState is in unnamed module of loader clojure.lang.DynamicClassLoader @57540fd0; clojure.lang.IFn is in unnamed module of loader 'app')

[yogthos]

Oh I see your problem, the issue is that *db* relies on env to get the database url. Since nothing is started by default you'd need to run (mount.core/start #'migtest.config/env #'migtest.db.core/*db*). I'll update the docs to make a note of that.

[winks]

Ah, that's the magic incantation that works. Thanks!

[winks]

Reopen, misclick.