I have a namespace that exposes common data-related functions (get-images, insert-user). I then have two database backends that have those same functions and implement them differently. They implement the interface as it were. Each backend is contained within a namespace.
I can't seem to be able to find a good solution on how to accomplish this.
I tried dynamically loading the ns but no luck. Once you do (:require [abc :as x]), the x isn't a real value.
I tried using defprotocol and deftype but that's all kinds of weird because the functions in the deftype need to be imported, too and that messes everything up for me.
Is there some idiomatic solution to this?
I don't see why protocols are not sufficient?
In ns data.api:
(ns data.api)
(defprotocol DB
(get-images [this])
(insert-user [this]))
In ns data.impl1:
(ns data.impl1
(:require [data.api :refer :all]))
(defrecord Database1 [connection-params]
DB
(get-images [_] ...)
(insert-user [_] ...))
Same thing in ns data.impl2.
Then when you go to use a particular db, just create the correct record:
(ns data.user
(:require [data.api :refer :all])
[data.impl1 :refer (->Database1)])
(defn use-db []
(let [db1 (->Database1 {})]
(get-images db1)))
Related
What is the difference between core & inope?
I have a very brief idea that core is like the main equivalent in Java. And inope is like an interface between java and clojure, although I dont understand the purpose of inope entirely.
I found this in a project and this is my understanding:
inope.clj is used for writing java clojure interoperable functions.
The namespace contents imply that it functions like core.clj here.
in this inope.clj file, they have imported dependencies and defined java-clojure interoperable functions in gen-class as such :
(ns prject-avon.inope
(:require [prject-avon.ioutil :as utl]
[aero.core :as aero-core :refer (read-config)]
[clojure.java.data :as clj-data]
[malli.core :as m]
[malli.util :as mu]
[malli.instrument :as mi]
[malli.error :as me]
[malli.json-schema :as json-schema]
(:gen-class
:methods [ ^{:static true} [validateData [Object String] Boolean]
]))
<Functions are defined here>
Those are just names, there's no significance to them. In particular, I've never heard of inope myself. The only way you can reliably judge is by the namespace's contents and their usage. It's also very possible that a single namespace contains all sorts of unrelated stuff.
I'm trying to load two namespaces from the library "spurious-aws-sdk-helper" (which by the way I've installed locally - this is me testing it before deploying to Clojars). And I'm loading the namespaces from inside an if statement.
Once the namespaces are loaded I call a function which is provided by one of the loaded namespaces.
The problem is that when executing the code via lein ring server I get a Java exception informing me that the namespace I'm trying to access isn't available.
But if I run lein repl and then (use 'spurious-clojure-example.routes.home) the relevant top level namespace; then (require '[spurious-aws-sdk-helper.core :as core]) the namespace - much like in the code I'll linked to in a moment demonstrates - then the namespace WILL be available and subsequently the call to the function won't error?
I'm not sure if it's one of those errors which are misleading and in fact it's not the namespace I'm trying to require that's the problem, but something inside of it that's the issue? But if that was true then why would it work when called manually by myself within lein repl?
The code I'm referring to is: https://github.com/Integralist/spurious-clojure-example/blob/baseline/src/spurious_clojure_example/routes/home.clj#L9-L10
(ns spurious-clojure-example.routes.home
(:use [amazonica.aws.s3])
(:require [compojure.core :refer :all]
[environ.core :refer [env]]
[spurious-clojure-example.views.layout :as layout]))
(if (env :debug)
(do
(require '[spurious-aws-sdk-helper.core :as core])
(require '[spurious-aws-sdk-helper.utils :refer [endpoint cred]])
(core/configure {:s3 "test-bucket4"
:sqs "test-queue4"
:ddb (slurp "./resources/config/schema.yaml")})))
(def bucket-path "news-archive/dev/election2014-council_title")
(def content
(apply str (line-seq
(clojure.java.io/reader
(:object-content
(get-object (cred (endpoint :spurious-s3)) :bucket-name "shared" :key bucket-path))))))
(defn home []
(layout/common [:h1 content]))
(defroutes home-routes
(GET "/" [] (home)))
It's the (core/configure ...) call that triggers a Java exception saying "core" namespace isn't available. But running the following code from lein repl works fine...
(use 'spurious-clojure-example.routes.home)
(require '[spurious-aws-sdk-helper.core :as core])
(core/configure ...rest of code...)
UPDATE 1:
Just to clarify I've updated the code as follows...
(when (env :debug)
(require '[spurious-aws-sdk-helper.core :as core])
(require '[spurious-aws-sdk-helper.utils :refer [endpoint cred]])
(core/configure
{:s3 "test-bucket7"
:sqs "test-queue9"
:ddb (slurp "./resources/config/schema.yaml")}))
...and when running it within the REPL it works fine.
The problem is when running it via lein ring server.
I've started reading about (ns-resolve) here: http://technomancy.us/143
But the solution it suggests: (ns-resolve 'core 'configure) didn't work; it just threw an Unable to resolve symbol: core in this context error.
I created a app with lein new compojure-app and when :debug value is truthy, require clojure.string :as str and then also printing something to shell.
The code below works via lein ring server. I tested it with :debug values true and false. I see in your example, you use environ so, I put {:debug true} or {:debug false} in .lein-env.
(ns integralist.handler
(:require [compojure.core :refer [defroutes routes]]
[ring.middleware.resource :refer [wrap-resource]]
[ring.middleware.file-info :refer [wrap-file-info]]
[hiccup.middleware :refer [wrap-base-url]]
[compojure.handler :as handler]
[compojure.route :as route]
[integralist.routes.home :refer [home-routes]]
[environ.core :refer [env]]))
(when (env :debug)
(require '[clojure.string :as str]))
(when (env :debug)
(defn it-works! []
(println "It works!:" (str/split "Clojure is Awesome" #" "))))
(defn init []
(println "integralist is starting")
(when (env :debug)
(it-works!)))
(defn destroy []
(println "integralist is shutting down"))
(defroutes app-routes
(route/resources "/")
(route/not-found "Not Found"))
(def app
(-> (routes home-routes app-routes)
(handler/site)
(wrap-base-url)))
Tried it with:
(when true ; also tried with false
(require '[clojure.string :as str])
(str/split "Clojure is awesome!" #" "))
=> No such namespace: str
I'm a tiny bit surprised as well since if and when should only evaluate the body of their expressions for the appropriate branch and not touch the other expressions. I did not expect a namespace error on false.
More surprising is I did not expect a namespace error on true as well. I'd guess it's some java compilation thing trying to resolve the namespace even before code evaluation. I don't know the specifics of why.
As for what you should do, this code is funky and I've never thought of or seen anyone doing anything similar. Unless there is some specific reason for doing this, the solution is simple: shove your requires to the very top in ns. There's no need to change anything else.
I'm working on a Liberator project in Clojure. I've defined a series of routes which return JSON data computed by logic in some other namespace. I would like to be able to change the namespace that implements the logic programmatically so I can do something like this:
JAVA_OPTS='-DgameLogicNamespace=foo.logic.mock' lein ring server-headless 8080
I am currently doing it like this:
(ns foo.routes
(:require [compojure.core :refer :all]
[liberator.core :as lib :refer [defresource request-method-in]]
[liberator.representation :refer [ring-response]]))
(require
(vec
(cons (symbol (System/getProperty "gameLogicNamespace" "foo.logic.real"))
'[:as logic])))
This works, but feels a bit clunky. Is there an idiomatic way to accomplish what I want?
One of my main motivations is actually for unit testing routes with mock data, so if there's a nice solution for providing the mock logic only in tests (and not as a JVM system property), suggestions are welcome.
One of my main motivations is actually for unit testing routes with mock data, so if there's a nice solution for providing the mock logic only in tests (and not as a JVM system property), suggestions are welcome.
If you haven't already, take a look at ring-mock for some nice utilities to generate mock requests to test your Ring handlers.
If you're interested in providing mock versions of functions that provide the implementation of your application logic during unit tests, consider using with-redefs; it's pretty much custom-made for this purpose.
(ns my-app.handlers-test
(:require [clojure.test]
[my-app.handlers :as h]
[my-app.logic :as l]
[ring.mock.request :as r]))
(deftest test-simple-handler
(with-redefs [l/my-complicated-logic #(update-in % [:a] inc)]
(is (= {:a 2}
(h/my-handler (r/request :post "/foo" {:a 1}))))))
What advantage does using :refer in :require have over using :only in :use? Are the following synonymous?
(ns so.example (:use [my.lib :only [function]]))
and
(ns so.example (:require [my.lib :refer [function]]))
Main idea of adding :refer to :require is to get rid completely of :use, leaving only one operator to load other packages. You can emulate existing :use with (:require [my.lib :refer :all])...
yes, they are equivalent,
:refer and :require are the basic operations required to build namespaces. :use is more convienient
:require causes classes to be loaded
:refer adds things to the name space which is really just a map (actually a couple of maps)
:use is :refer + :require
as much is it may look like it, there really is no magic to namespaces
if you make a namespace like this
(ns so.example (:use my.lib))
the equivalent with :require would be:
(ns so.example (:require [my.lib :refer [function1 function2 function3
list every function in example
here and remember to keep it
up to date ]]))
As of the 1.4.0 release, there's no longer a good reason to use use. Use require :refer instead. From the Clojure 1.4.0 changelog: "require can now take a :refer option. :refer takes a list of symbols to refer from the namespace or :all to bring in all public vars."
(from https://8thlight.com/blog/colin-jones/2010/12/05/clojure-libs-and-namespaces-require-use-import-and-ns.html)
When using clojure.string, I receive the following warnings
WARNING: replace already refers to: #'clojure.core/replace in namespace: tutorial.regexp, being replaced by: #'clojure.string/replace
WARNING: reverse already refers to: #'clojure.core/reverse in namespace: tutorial.regexp, being replaced by: #'clojure.string/reverse
my clojure script is:
(ns play-with-it
(:use [clojure.string]))
Is there any way to fix those warnings?
Yes, switch to
(ns play-with-it
(:require [clojure.string :as string]))
and then say e.g.
(string/replace ...)
to call clojure.string's replace function.
With :use, you bring in all Vars from clojure.string directly into your namespace, and since some of those have names clashing with Vars in clojure.core, you get the warning. Then you'd have to say clojure.core/replace to get at what's usually simply called replace.
The clash of names is by design; clojure.string is meant to be required with an alias like this. str and string are the most frequently chosen aliases.
In addition to Michał's answer, you can exclude vars from clojure.core:
user=> (ns foo)
nil
foo=> (defn map [])
WARNING: map already refers to: #'clojure.core/map in namespace: foo, being replaced by: #'foo/map
#'foo/map
foo=> (ns bar
(:refer-clojure :exclude [map]))
nil
bar=> (defn map [])
#'bar/map
In addition to Alex's answer you can also refer only the vars you want from a given namespace.
(ns foo.core
(:use [clojure.string :only (replace-first)]))
This would not throw a warning since replace-first is not in clojure.core. However, you would still receive a warning if you did the following:
(ns foo.core
(:use [clojure.string :only (replace)]))
In general it seems people are tending toward (ns foo.bar (:require [foo.bar :as baz])).
Since Clojure 1.4 you can refer the individual functions you need from a namespace using :require with a :refer:
(ns play-with-it
(:require [clojure.string :refer [replace-first]]))
This is now recommended over :use.
Assuming you don't need the clojure.string/replace or clojure.string/reverse, that would also remove the warnings.
See this SO question and this JIRA issue for more details.